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2. Getting Help

If you have trouble with Spring Boot, we would like to help.

All of Spring Boot is open source, including the documentation. If you find problems with the docs or if you want to improve them, please get involved.

3. Documentation Overview

This section provides a brief overview of Spring Boot reference documentation. It serves as a map for the rest of the document.

The latest copy of this document is available at docs.spring.io/spring-boot/docs/current/reference/.

3.1. First Steps

If you are getting started with Spring Boot or 'Spring' in general, start with the following topics:

3.2. Upgrading From an Earlier Version

You should always ensure that you are running a supported version of Spring Boot.

Depending on the version that you are upgrading to, you can find some additional tips here:

3.3. Developing With Spring Boot

Ready to actually start using Spring Boot? We have you covered:

3.4. Learning About Spring Boot Features

Need more details about Spring Boot’s core features? The following content is for you:

3.5. Web

If you develop Spring Boot web applications, take a look at the following content:

3.6. Data

If your application deals with a datastore, you can see how to configure that here:

3.8. IO

If your application needs IO capabilities, see one or more of the following sections:

3.9. Container Images

Spring Boot provides first-class support for building efficient container images. You can read more about it here:

3.10. Moving to Production

When you are ready to push your Spring Boot application to production, we have some tricks that you might like:

3.11. Advanced Topics

Finally, we have a few topics for more advanced users:

4. Getting Started

If you are getting started with Spring Boot, or “Spring” in general, start by reading this section. It answers the basic “what?”, “how?” and “why?” questions. It includes an introduction to Spring Boot, along with installation instructions. We then walk you through building your first Spring Boot application, discussing some core principles as we go.

4.1. Introducing Spring Boot

Spring Boot helps you to create stand-alone, production-grade Spring-based applications that you can run. We take an opinionated view of the Spring platform and third-party libraries, so that you can get started with minimum fuss. Most Spring Boot applications need very little Spring configuration.

You can use Spring Boot to create Java applications that can be started by using java -jar or more traditional war deployments. We also provide a command line tool that runs “spring scripts”.

Our primary goals are:

  • Provide a radically faster and widely accessible getting-started experience for all Spring development.

  • Be opinionated out of the box but get out of the way quickly as requirements start to diverge from the defaults.

  • Provide a range of non-functional features that are common to large classes of projects (such as embedded servers, security, metrics, health checks, and externalized configuration).

  • Absolutely no code generation and no requirement for XML configuration.

4.2. System Requirements

Spring Boot 2.7.18 requires Java 8 and is compatible up to and including Java 21. Spring Framework 5.3.31 or above is also required.

Explicit build support is provided for the following build tools:

Build Tool Version

Maven

3.5+

Gradle

6.8.x, 6.9.x, 7.x, and 8.x

4.2.1. Servlet Containers

Spring Boot supports the following embedded servlet containers:

Name Servlet Version

Tomcat 9.0

4.0

Jetty 9.4

3.1

Jetty 10.0

4.0

Undertow 2.0

4.0

You can also deploy Spring Boot applications to any Servlet 3.1 or 4.0 compatible container.

4.3. Installing Spring Boot

Spring Boot can be used with “classic” Java development tools or installed as a command line tool. Either way, you need Java SDK v1.8 or higher. Before you begin, you should check your current Java installation by using the following command:

$ java -version

If you are new to Java development or if you want to experiment with Spring Boot, you might want to try the Spring Boot CLI (Command Line Interface) first. Otherwise, read on for “classic” installation instructions.

4.3.1. Installation Instructions for the Java Developer

You can use Spring Boot in the same way as any standard Java library. To do so, include the appropriate spring-boot-*.jar files on your classpath. Spring Boot does not require any special tools integration, so you can use any IDE or text editor. Also, there is nothing special about a Spring Boot application, so you can run and debug a Spring Boot application as you would any other Java program.

Although you could copy Spring Boot jars, we generally recommend that you use a build tool that supports dependency management (such as Maven or Gradle).

Maven Installation

Spring Boot is compatible with Apache Maven 3.3 or above. If you do not already have Maven installed, you can follow the instructions at maven.apache.org.

On many operating systems, Maven can be installed with a package manager. If you use OSX Homebrew, try brew install maven. Ubuntu users can run sudo apt-get install maven. Windows users with Chocolatey can run choco install maven from an elevated (administrator) prompt.

Spring Boot dependencies use the org.springframework.boot groupId. Typically, your Maven POM file inherits from the spring-boot-starter-parent project and declares dependencies to one or more “Starters”. Spring Boot also provides an optional Maven plugin to create executable jars.

More details on getting started with Spring Boot and Maven can be found in the Getting Started section of the Maven plugin’s reference guide.

Gradle Installation

Spring Boot is compatible with Gradle 6.8, 6.9, 7.x, and 8.x. If you do not already have Gradle installed, you can follow the instructions at gradle.org.

Spring Boot dependencies can be declared by using the org.springframework.boot group. Typically, your project declares dependencies to one or more “Starters”. Spring Boot provides a useful Gradle plugin that can be used to simplify dependency declarations and to create executable jars.

Gradle Wrapper

The Gradle Wrapper provides a nice way of “obtaining” Gradle when you need to build a project. It is a small script and library that you commit alongside your code to bootstrap the build process. See docs.gradle.org/current/userguide/gradle_wrapper.html for details.

More details on getting started with Spring Boot and Gradle can be found in the Getting Started section of the Gradle plugin’s reference guide.

4.3.2. Installing the Spring Boot CLI

The Spring Boot CLI (Command Line Interface) is a command line tool that you can use to quickly prototype with Spring. It lets you run Groovy scripts, which means that you have a familiar Java-like syntax without so much boilerplate code.

You do not need to use the CLI to work with Spring Boot, but it is a quick way to get a Spring application off the ground without an IDE.

Manual Installation

You can download the Spring CLI distribution from one of the following locations:

Once downloaded, follow the INSTALL.txt instructions from the unpacked archive. In summary, there is a spring script (spring.bat for Windows) in a bin/ directory in the .zip file. Alternatively, you can use java -jar with the .jar file (the script helps you to be sure that the classpath is set correctly).

Installation with SDKMAN!

SDKMAN! (The Software Development Kit Manager) can be used for managing multiple versions of various binary SDKs, including Groovy and the Spring Boot CLI. Get SDKMAN! from sdkman.io and install Spring Boot by using the following commands:

$ sdk install springboot
$ spring --version
Spring CLI v2.7.18

If you develop features for the CLI and want access to the version you built, use the following commands:

$ sdk install springboot dev /path/to/spring-boot/spring-boot-cli/target/spring-boot-cli-2.7.18-bin/spring-2.7.18/
$ sdk default springboot dev
$ spring --version
Spring CLI v2.7.18

The preceding instructions install a local instance of spring called the dev instance. It points at your target build location, so every time you rebuild Spring Boot, spring is up-to-date.

You can see it by running the following command:

$ sdk ls springboot

================================================================================
Available Springboot Versions
================================================================================
> + dev
* 2.7.18

================================================================================
+ - local version
* - installed
> - currently in use
================================================================================
OSX Homebrew Installation

If you are on a Mac and use Homebrew, you can install the Spring Boot CLI by using the following commands:

$ brew tap spring-io/tap
$ brew install spring-boot

Homebrew installs spring to /usr/local/bin.

If you do not see the formula, your installation of brew might be out-of-date. In that case, run brew update and try again.
MacPorts Installation

If you are on a Mac and use MacPorts, you can install the Spring Boot CLI by using the following command:

$ sudo port install spring-boot-cli
Command-line Completion

The Spring Boot CLI includes scripts that provide command completion for the BASH and zsh shells. You can source the script (also named spring) in any shell or put it in your personal or system-wide bash completion initialization. On a Debian system, the system-wide scripts are in /shell-completion/bash and all scripts in that directory are executed when a new shell starts. For example, to run the script manually if you have installed by using SDKMAN!, use the following commands:

$ . ~/.sdkman/candidates/springboot/current/shell-completion/bash/spring
$ spring <HIT TAB HERE>
  grab  help  jar  run  test  version
If you install the Spring Boot CLI by using Homebrew or MacPorts, the command-line completion scripts are automatically registered with your shell.
Windows Scoop Installation

If you are on a Windows and use Scoop, you can install the Spring Boot CLI by using the following commands:

> scoop bucket add extras
> scoop install springboot

Scoop installs spring to ~/scoop/apps/springboot/current/bin.

If you do not see the app manifest, your installation of scoop might be out-of-date. In that case, run scoop update and try again.
Quick-start Spring CLI Example

You can use the following web application to test your installation. To start, create a file called app.groovy, as follows:

@RestController
class ThisWillActuallyRun {

    @RequestMapping("/")
    String home() {
        "Hello World!"
    }

}

Then run it from a shell, as follows:

$ spring run app.groovy
The first run of your application is slow, as dependencies are downloaded. Subsequent runs are much quicker.

Open localhost:8080 in your favorite web browser. You should see the following output:

Hello World!

4.4. Developing Your First Spring Boot Application

This section describes how to develop a small “Hello World!” web application that highlights some of Spring Boot’s key features. We use Maven to build this project, since most IDEs support it.

The spring.io web site contains many “Getting Started” guides that use Spring Boot. If you need to solve a specific problem, check there first.

You can shortcut the steps below by going to start.spring.io and choosing the "Web" starter from the dependencies searcher. Doing so generates a new project structure so that you can start coding right away. Check the start.spring.io user guide for more details.

Before we begin, open a terminal and run the following commands to ensure that you have valid versions of Java and Maven installed:

$ java -version
java version "1.8.0_102"
Java(TM) SE Runtime Environment (build 1.8.0_102-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.102-b14, mixed mode)
$ mvn -v
Apache Maven 3.5.4 (1edded0938998edf8bf061f1ceb3cfdeccf443fe; 2018-06-17T14:33:14-04:00)
Maven home: /usr/local/Cellar/maven/3.3.9/libexec
Java version: 1.8.0_102, vendor: Oracle Corporation
This sample needs to be created in its own directory. Subsequent instructions assume that you have created a suitable directory and that it is your current directory.

4.4.1. Creating the POM

We need to start by creating a Maven pom.xml file. The pom.xml is the recipe that is used to build your project. Open your favorite text editor and add the following:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>myproject</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.7.18</version>
    </parent>

    <!-- Additional lines to be added here... -->

</project>

The preceding listing should give you a working build. You can test it by running mvn package (for now, you can ignore the “jar will be empty - no content was marked for inclusion!” warning).

At this point, you could import the project into an IDE (most modern Java IDEs include built-in support for Maven). For simplicity, we continue to use a plain text editor for this example.

4.4.2. Adding Classpath Dependencies

Spring Boot provides a number of “Starters” that let you add jars to your classpath. Our applications for smoke tests use the spring-boot-starter-parent in the parent section of the POM. The spring-boot-starter-parent is a special starter that provides useful Maven defaults. It also provides a dependency-management section so that you can omit version tags for “blessed” dependencies.

Other “Starters” provide dependencies that you are likely to need when developing a specific type of application. Since we are developing a web application, we add a spring-boot-starter-web dependency. Before that, we can look at what we currently have by running the following command:

$ mvn dependency:tree

[INFO] com.example:myproject:jar:0.0.1-SNAPSHOT

The mvn dependency:tree command prints a tree representation of your project dependencies. You can see that spring-boot-starter-parent provides no dependencies by itself. To add the necessary dependencies, edit your pom.xml and add the spring-boot-starter-web dependency immediately below the parent section:

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
</dependencies>

If you run mvn dependency:tree again, you see that there are now a number of additional dependencies, including the Tomcat web server and Spring Boot itself.

4.4.3. Writing the Code

To finish our application, we need to create a single Java file. By default, Maven compiles sources from src/main/java, so you need to create that directory structure and then add a file named src/main/java/MyApplication.java to contain the following code:

Java
package com.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@SpringBootApplication
public class MyApplication {

    @RequestMapping("/")
    String home() {
        return "Hello World!";
    }

    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }

}
Kotlin
import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication
import org.springframework.web.bind.annotation.RequestMapping
import org.springframework.web.bind.annotation.RestController

@RestController
@SpringBootApplication
class MyApplication {

    @RequestMapping("/")
    fun home() = "Hello World!"

}

fun main(args: Array<String>) {
    runApplication<MyApplication>(*args)
}

Although there is not much code here, quite a lot is going on. We step through the important parts in the next few sections.

The @RestController and @RequestMapping Annotations

The first annotation on our MyApplication class is @RestController. This is known as a stereotype annotation. It provides hints for people reading the code and for Spring that the class plays a specific role. In this case, our class is a web @Controller, so Spring considers it when handling incoming web requests.

The @RequestMapping annotation provides “routing” information. It tells Spring that any HTTP request with the / path should be mapped to the home method. The @RestController annotation tells Spring to render the resulting string directly back to the caller.

The @RestController and @RequestMapping annotations are Spring MVC annotations (they are not specific to Spring Boot). See the MVC section in the Spring Reference Documentation for more details.
The @SpringBootApplication Annotation

The second class-level annotation is @SpringBootApplication. This annotation is known as a meta-annotation, it combines @SpringBootConfiguration, @EnableAutoConfiguration and @ComponentScan.

Of those, the annotation we’re most interested in here is @EnableAutoConfiguration. @EnableAutoConfiguration tells Spring Boot to “guess” how you want to configure Spring, based on the jar dependencies that you have added. Since spring-boot-starter-web added Tomcat and Spring MVC, the auto-configuration assumes that you are developing a web application and sets up Spring accordingly.

Starters and Auto-configuration

Auto-configuration is designed to work well with “Starters”, but the two concepts are not directly tied. You are free to pick and choose jar dependencies outside of the starters. Spring Boot still does its best to auto-configure your application.

The “main” Method

The final part of our application is the main method. This is a standard method that follows the Java convention for an application entry point. Our main method delegates to Spring Boot’s SpringApplication class by calling run. SpringApplication bootstraps our application, starting Spring, which, in turn, starts the auto-configured Tomcat web server. We need to pass MyApplication.class as an argument to the run method to tell SpringApplication which is the primary Spring component. The args array is also passed through to expose any command-line arguments.

4.4.4. Running the Example

At this point, your application should work. Since you used the spring-boot-starter-parent POM, you have a useful run goal that you can use to start the application. Type mvn spring-boot:run from the root project directory to start the application. You should see output similar to the following:

$ mvn spring-boot:run

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::  (v2.7.18)
....... . . .
....... . . . (log output here)
....... . . .
........ Started MyApplication in 2.222 seconds (JVM running for 6.514)

If you open a web browser to localhost:8080, you should see the following output:

Hello World!

To gracefully exit the application, press ctrl-c.

4.4.5. Creating an Executable Jar

We finish our example by creating a completely self-contained executable jar file that we could run in production. Executable jars (sometimes called “fat jars”) are archives containing your compiled classes along with all of the jar dependencies that your code needs to run.

Executable jars and Java

Java does not provide a standard way to load nested jar files (jar files that are themselves contained within a jar). This can be problematic if you are looking to distribute a self-contained application.

To solve this problem, many developers use “uber” jars. An uber jar packages all the classes from all the application’s dependencies into a single archive. The problem with this approach is that it becomes hard to see which libraries are in your application. It can also be problematic if the same filename is used (but with different content) in multiple jars.

Spring Boot takes a different approach and lets you actually nest jars directly.

To create an executable jar, we need to add the spring-boot-maven-plugin to our pom.xml. To do so, insert the following lines just below the dependencies section:

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
        </plugin>
    </plugins>
</build>
The spring-boot-starter-parent POM includes <executions> configuration to bind the repackage goal. If you do not use the parent POM, you need to declare this configuration yourself. See the plugin documentation for details.

Save your pom.xml and run mvn package from the command line, as follows:

$ mvn package

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building myproject 0.0.1-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] .... ..
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ myproject ---
[INFO] Building jar: /Users/developer/example/spring-boot-example/target/myproject-0.0.1-SNAPSHOT.jar
[INFO]
[INFO] --- spring-boot-maven-plugin:2.7.18:repackage (default) @ myproject ---
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------

If you look in the target directory, you should see myproject-0.0.1-SNAPSHOT.jar. The file should be around 18 MB in size. If you want to peek inside, you can use jar tvf, as follows:

$ jar tvf target/myproject-0.0.1-SNAPSHOT.jar

You should also see a much smaller file named myproject-0.0.1-SNAPSHOT.jar.original in the target directory. This is the original jar file that Maven created before it was repackaged by Spring Boot.

To run that application, use the java -jar command, as follows:

$ java -jar target/myproject-0.0.1-SNAPSHOT.jar

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::  (v2.7.18)
....... . . .
....... . . . (log output here)
....... . . .
........ Started MyApplication in 2.536 seconds (JVM running for 2.864)

As before, to exit the application, press ctrl-c.

4.5. What to Read Next

Hopefully, this section provided some of the Spring Boot basics and got you on your way to writing your own applications. If you are a task-oriented type of developer, you might want to jump over to spring.io and follow some of the getting started guides that solve specific “How do I do that with Spring?” problems. We also have Spring Boot-specific “How-to” reference documentation.

Otherwise, the next logical step is to read Developing with Spring Boot. If you are really impatient, you could also jump ahead and read about Spring Boot features.

5. Upgrading Spring Boot

Instructions for how to upgrade from earlier versions of Spring Boot are provided on the project wiki. Follow the links in the release notes section to find the version that you want to upgrade to.

Upgrading instructions are always the first item in the release notes. If you are more than one release behind, please make sure that you also review the release notes of the versions that you jumped.

5.1. Upgrading From 1.x

If you are upgrading from the 1.x release of Spring Boot, check the “migration guide” on the project wiki that provides detailed upgrade instructions. Check also the “release notes” for a list of “new and noteworthy” features for each release.

5.2. Upgrading to a New Feature Release

When upgrading to a new feature release, some properties may have been renamed or removed. Spring Boot provides a way to analyze your application’s environment and print diagnostics at startup, but also temporarily migrate properties at runtime for you. To enable that feature, add the following dependency to your project:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-properties-migrator</artifactId>
    <scope>runtime</scope>
</dependency>
Properties that are added late to the environment, such as when using @PropertySource, will not be taken into account.
Once you finish the migration, please make sure to remove this module from your project’s dependencies.

5.3. Upgrading the Spring Boot CLI

To upgrade an existing CLI installation, use the appropriate package manager command (for example, brew upgrade). If you manually installed the CLI, follow the standard instructions, remembering to update your PATH environment variable to remove any older references.

5.4. What to Read Next

Once you’ve decided to upgrade your application, you can find detailed information regarding specific features in the rest of the document.

Spring Boot’s documentation is specific to that version, so any information that you find in here will contain the most up-to-date changes that are in that version.

6. Developing with Spring Boot

This section goes into more detail about how you should use Spring Boot. It covers topics such as build systems, auto-configuration, and how to run your applications. We also cover some Spring Boot best practices. Although there is nothing particularly special about Spring Boot (it is just another library that you can consume), there are a few recommendations that, when followed, make your development process a little easier.

If you are starting out with Spring Boot, you should probably read the Getting Started guide before diving into this section.

6.1. Build Systems

It is strongly recommended that you choose a build system that supports dependency management and that can consume artifacts published to the “Maven Central” repository. We would recommend that you choose Maven or Gradle. It is possible to get Spring Boot to work with other build systems (Ant, for example), but they are not particularly well supported.

6.1.1. Dependency Management

Each release of Spring Boot provides a curated list of dependencies that it supports. In practice, you do not need to provide a version for any of these dependencies in your build configuration, as Spring Boot manages that for you. When you upgrade Spring Boot itself, these dependencies are upgraded as well in a consistent way.

You can still specify a version and override Spring Boot’s recommendations if you need to do so.

The curated list contains all the Spring modules that you can use with Spring Boot as well as a refined list of third party libraries. The list is available as a standard Bills of Materials (spring-boot-dependencies) that can be used with both Maven and Gradle.

Each release of Spring Boot is associated with a base version of the Spring Framework. We highly recommend that you not specify its version.

6.1.2. Maven

To learn about using Spring Boot with Maven, see the documentation for Spring Boot’s Maven plugin:

6.1.3. Gradle

To learn about using Spring Boot with Gradle, see the documentation for Spring Boot’s Gradle plugin:

6.1.4. Ant

It is possible to build a Spring Boot project using Apache Ant+Ivy. The spring-boot-antlib “AntLib” module is also available to help Ant create executable jars.

To declare dependencies, a typical ivy.xml file looks something like the following example:

<ivy-module version="2.0">
    <info organisation="org.springframework.boot" module="spring-boot-sample-ant" />
    <configurations>
        <conf name="compile" description="everything needed to compile this module" />
        <conf name="runtime" extends="compile" description="everything needed to run this module" />
    </configurations>
    <dependencies>
        <dependency org="org.springframework.boot" name="spring-boot-starter"
            rev="${spring-boot.version}" conf="compile" />
    </dependencies>
</ivy-module>

A typical build.xml looks like the following example:

<project
    xmlns:ivy="antlib:org.apache.ivy.ant"
    xmlns:spring-boot="antlib:org.springframework.boot.ant"
    name="myapp" default="build">

    <property name="spring-boot.version" value="2.7.18" />

    <target name="resolve" description="--> retrieve dependencies with ivy">
        <ivy:retrieve pattern="lib/[conf]/[artifact]-[type]-[revision].[ext]" />
    </target>

    <target name="classpaths" depends="resolve">
        <path id="compile.classpath">
            <fileset dir="lib/compile" includes="*.jar" />
        </path>
    </target>

    <target name="init" depends="classpaths">
        <mkdir dir="build/classes" />
    </target>

    <target name="compile" depends="init" description="compile">
        <javac srcdir="src/main/java" destdir="build/classes" classpathref="compile.classpath" />
    </target>

    <target name="build" depends="compile">
        <spring-boot:exejar destfile="build/myapp.jar" classes="build/classes">
            <spring-boot:lib>
                <fileset dir="lib/runtime" />
            </spring-boot:lib>
        </spring-boot:exejar>
    </target>
</project>
If you do not want to use the spring-boot-antlib module, see the Build an Executable Archive From Ant without Using spring-boot-antlib “How-to” .

6.1.5. Starters

Starters are a set of convenient dependency descriptors that you can include in your application. You get a one-stop shop for all the Spring and related technologies that you need without having to hunt through sample code and copy-paste loads of dependency descriptors. For example, if you want to get started using Spring and JPA for database access, include the spring-boot-starter-data-jpa dependency in your project.

The starters contain a lot of the dependencies that you need to get a project up and running quickly and with a consistent, supported set of managed transitive dependencies.

What is in a name

All official starters follow a similar naming pattern; spring-boot-starter-*, where * is a particular type of application. This naming structure is intended to help when you need to find a starter. The Maven integration in many IDEs lets you search dependencies by name. For example, with the appropriate Eclipse or Spring Tools plugin installed, you can press ctrl-space in the POM editor and type “spring-boot-starter” for a complete list.

As explained in the “Creating Your Own Starter” section, third party starters should not start with spring-boot, as it is reserved for official Spring Boot artifacts. Rather, a third-party starter typically starts with the name of the project. For example, a third-party starter project called thirdpartyproject would typically be named thirdpartyproject-spring-boot-starter.

The following application starters are provided by Spring Boot under the org.springframework.boot group:

Table 1. Spring Boot application starters
Name Description

spring-boot-starter

Core starter, including auto-configuration support, logging and YAML

spring-boot-starter-activemq

Starter for JMS messaging using Apache ActiveMQ

spring-boot-starter-amqp

Starter for using Spring AMQP and Rabbit MQ

spring-boot-starter-aop

Starter for aspect-oriented programming with Spring AOP and AspectJ

spring-boot-starter-artemis

Starter for JMS messaging using Apache Artemis

spring-boot-starter-batch

Starter for using Spring Batch

spring-boot-starter-cache

Starter for using Spring Framework’s caching support

spring-boot-starter-data-cassandra

Starter for using Cassandra distributed database and Spring Data Cassandra

spring-boot-starter-data-cassandra-reactive

Starter for using Cassandra distributed database and Spring Data Cassandra Reactive

spring-boot-starter-data-couchbase

Starter for using Couchbase document-oriented database and Spring Data Couchbase

spring-boot-starter-data-couchbase-reactive

Starter for using Couchbase document-oriented database and Spring Data Couchbase Reactive

spring-boot-starter-data-elasticsearch

Starter for using Elasticsearch search and analytics engine and Spring Data Elasticsearch

spring-boot-starter-data-jdbc

Starter for using Spring Data JDBC

spring-boot-starter-data-jpa

Starter for using Spring Data JPA with Hibernate

spring-boot-starter-data-ldap

Starter for using Spring Data LDAP

spring-boot-starter-data-mongodb

Starter for using MongoDB document-oriented database and Spring Data MongoDB

spring-boot-starter-data-mongodb-reactive

Starter for using MongoDB document-oriented database and Spring Data MongoDB Reactive

spring-boot-starter-data-neo4j

Starter for using Neo4j graph database and Spring Data Neo4j

spring-boot-starter-data-r2dbc

Starter for using Spring Data R2DBC

spring-boot-starter-data-redis

Starter for using Redis key-value data store with Spring Data Redis and the Lettuce client

spring-boot-starter-data-redis-reactive

Starter for using Redis key-value data store with Spring Data Redis reactive and the Lettuce client

spring-boot-starter-data-rest

Starter for exposing Spring Data repositories over REST using Spring Data REST and Spring MVC

spring-boot-starter-freemarker

Starter for building MVC web applications using FreeMarker views

spring-boot-starter-graphql

Starter for building GraphQL applications with Spring GraphQL

spring-boot-starter-groovy-templates

Starter for building MVC web applications using Groovy Templates views

spring-boot-starter-hateoas

Starter for building hypermedia-based RESTful web application with Spring MVC and Spring HATEOAS

spring-boot-starter-integration

Starter for using Spring Integration

spring-boot-starter-jdbc

Starter for using JDBC with the HikariCP connection pool

spring-boot-starter-jersey

Starter for building RESTful web applications using JAX-RS and Jersey. An alternative to spring-boot-starter-web

spring-boot-starter-jooq

Starter for using jOOQ to access SQL databases with JDBC. An alternative to spring-boot-starter-data-jpa or spring-boot-starter-jdbc

spring-boot-starter-json

Starter for reading and writing json

spring-boot-starter-jta-atomikos

Starter for JTA transactions using Atomikos

spring-boot-starter-mail

Starter for using Java Mail and Spring Framework’s email sending support

spring-boot-starter-mustache

Starter for building web applications using Mustache views

spring-boot-starter-oauth2-client

Starter for using Spring Security’s OAuth2/OpenID Connect client features

spring-boot-starter-oauth2-resource-server

Starter for using Spring Security’s OAuth2 resource server features

spring-boot-starter-quartz

Starter for using the Quartz scheduler

spring-boot-starter-rsocket

Starter for building RSocket clients and servers

spring-boot-starter-security

Starter for using Spring Security

spring-boot-starter-test

Starter for testing Spring Boot applications with libraries including JUnit Jupiter, Hamcrest and Mockito

spring-boot-starter-thymeleaf

Starter for building MVC web applications using Thymeleaf views

spring-boot-starter-validation

Starter for using Java Bean Validation with Hibernate Validator

spring-boot-starter-web

Starter for building web, including RESTful, applications using Spring MVC. Uses Tomcat as the default embedded container

spring-boot-starter-web-services

Starter for using Spring Web Services

spring-boot-starter-webflux

Starter for building WebFlux applications using Spring Framework’s Reactive Web support

spring-boot-starter-websocket

Starter for building WebSocket applications using Spring Framework’s MVC WebSocket support

In addition to the application starters, the following starters can be used to add production ready features:

Table 2. Spring Boot production starters
Name Description

spring-boot-starter-actuator

Starter for using Spring Boot’s Actuator which provides production ready features to help you monitor and manage your application

Finally, Spring Boot also includes the following starters that can be used if you want to exclude or swap specific technical facets:

Table 3. Spring Boot technical starters
Name Description

spring-boot-starter-jetty

Starter for using Jetty as the embedded servlet container. An alternative to spring-boot-starter-tomcat

spring-boot-starter-log4j2

Starter for using Log4j2 for logging. An alternative to spring-boot-starter-logging

spring-boot-starter-logging

Starter for logging using Logback. Default logging starter

spring-boot-starter-reactor-netty

Starter for using Reactor Netty as the embedded reactive HTTP server.

spring-boot-starter-tomcat

Starter for using Tomcat as the embedded servlet container. Default servlet container starter used by spring-boot-starter-web

spring-boot-starter-undertow

Starter for using Undertow as the embedded servlet container. An alternative to spring-boot-starter-tomcat

To learn how to swap technical facets, please see the how-to documentation for swapping web server and logging system.

For a list of additional community contributed starters, see the README file in the spring-boot-starters module on GitHub.

6.2. Structuring Your Code

Spring Boot does not require any specific code layout to work. However, there are some best practices that help.

6.2.1. Using the “default” Package

When a class does not include a package declaration, it is considered to be in the “default package”. The use of the “default package” is generally discouraged and should be avoided. It can cause particular problems for Spring Boot applications that use the @ComponentScan, @ConfigurationPropertiesScan, @EntityScan, or @SpringBootApplication annotations, since every class from every jar is read.

We recommend that you follow Java’s recommended package naming conventions and use a reversed domain name (for example, com.example.project).

6.2.2. Locating the Main Application Class

We generally recommend that you locate your main application class in a root package above other classes. The @SpringBootApplication annotation is often placed on your main class, and it implicitly defines a base “search package” for certain items. For example, if you are writing a JPA application, the package of the @SpringBootApplication annotated class is used to search for @Entity items. Using a root package also allows component scan to apply only on your project.

If you do not want to use @SpringBootApplication, the @EnableAutoConfiguration and @ComponentScan annotations that it imports defines that behavior so you can also use those instead.

The following listing shows a typical layout:

com
 +- example
     +- myapplication
         +- MyApplication.java
         |
         +- customer
         |   +- Customer.java
         |   +- CustomerController.java
         |   +- CustomerService.java
         |   +- CustomerRepository.java
         |
         +- order
             +- Order.java
             +- OrderController.java
             +- OrderService.java
             +- OrderRepository.java

The MyApplication.java file would declare the main method, along with the basic @SpringBootApplication, as follows:

Java
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MyApplication {

    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }

}
Kotlin
import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class MyApplication

fun main(args: Array<String>) {
    runApplication<MyApplication>(*args)
}

6.3. Configuration Classes

Spring Boot favors Java-based configuration. Although it is possible to use SpringApplication with XML sources, we generally recommend that your primary source be a single @Configuration class. Usually the class that defines the main method is a good candidate as the primary @Configuration.

Many Spring configuration examples have been published on the Internet that use XML configuration. If possible, always try to use the equivalent Java-based configuration. Searching for Enable* annotations can be a good starting point.

6.3.1. Importing Additional Configuration Classes

You need not put all your @Configuration into a single class. The @Import annotation can be used to import additional configuration classes. Alternatively, you can use @ComponentScan to automatically pick up all Spring components, including @Configuration classes.

6.3.2. Importing XML Configuration

If you absolutely must use XML based configuration, we recommend that you still start with a @Configuration class. You can then use an @ImportResource annotation to load XML configuration files.

6.4. Auto-configuration

Spring Boot auto-configuration attempts to automatically configure your Spring application based on the jar dependencies that you have added. For example, if HSQLDB is on your classpath, and you have not manually configured any database connection beans, then Spring Boot auto-configures an in-memory database.

You need to opt-in to auto-configuration by adding the @EnableAutoConfiguration or @SpringBootApplication annotations to one of your @Configuration classes.

You should only ever add one @SpringBootApplication or @EnableAutoConfiguration annotation. We generally recommend that you add one or the other to your primary @Configuration class only.

6.4.1. Gradually Replacing Auto-configuration

Auto-configuration is non-invasive. At any point, you can start to define your own configuration to replace specific parts of the auto-configuration. For example, if you add your own DataSource bean, the default embedded database support backs away.

If you need to find out what auto-configuration is currently being applied, and why, start your application with the --debug switch. Doing so enables debug logs for a selection of core loggers and logs a conditions report to the console.

6.4.2. Disabling Specific Auto-configuration Classes

If you find that specific auto-configuration classes that you do not want are being applied, you can use the exclude attribute of @SpringBootApplication to disable them, as shown in the following example:

Java
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;

@SpringBootApplication(exclude = { DataSourceAutoConfiguration.class })
public class MyApplication {

}
Kotlin
import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration

@SpringBootApplication(exclude = [DataSourceAutoConfiguration::class])
class MyApplication

If the class is not on the classpath, you can use the excludeName attribute of the annotation and specify the fully qualified name instead. If you prefer to use @EnableAutoConfiguration rather than @SpringBootApplication, exclude and excludeName are also available. Finally, you can also control the list of auto-configuration classes to exclude by using the spring.autoconfigure.exclude property.

You can define exclusions both at the annotation level and by using the property.
Even though auto-configuration classes are public, the only aspect of the class that is considered public API is the name of the class which can be used for disabling the auto-configuration. The actual contents of those classes, such as nested configuration classes or bean methods are for internal use only and we do not recommend using those directly.

6.4.3. Auto-configuration Packages

Auto-configuration packages are the packages that various auto-configured features look in by default when scanning for things such as entities and Spring Data repositories. The @EnableAutoConfiguration annotation (either directly or through its presence on @SpringBootApplication) determines the default auto-configuration package. Additional packages can be configured using the @AutoConfigurationPackage annotation.

6.5. Spring Beans and Dependency Injection

You are free to use any of the standard Spring Framework techniques to define your beans and their injected dependencies. We generally recommend using constructor injection to wire up dependencies and @ComponentScan to find beans.

If you structure your code as suggested above (locating your application class in a top package), you can add @ComponentScan without any arguments or use the @SpringBootApplication annotation which implicitly includes it. All of your application components (@Component, @Service, @Repository, @Controller, and others) are automatically registered as Spring Beans.

The following example shows a @Service Bean that uses constructor injection to obtain a required RiskAssessor bean:

Java
import org.springframework.stereotype.Service;

@Service
public class MyAccountService implements AccountService {

    private final RiskAssessor riskAssessor;

    public MyAccountService(RiskAssessor riskAssessor) {
        this.riskAssessor = riskAssessor;
    }

    // ...

}
Kotlin
import org.springframework.stereotype.Service

@Service
class MyAccountService(private val riskAssessor: RiskAssessor) : AccountService

If a bean has more than one constructor, you will need to mark the one you want Spring to use with @Autowired:

Java
import java.io.PrintStream;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class MyAccountService implements AccountService {

    private final RiskAssessor riskAssessor;

    private final PrintStream out;

    @Autowired
    public MyAccountService(RiskAssessor riskAssessor) {
        this.riskAssessor = riskAssessor;
        this.out = System.out;
    }

    public MyAccountService(RiskAssessor riskAssessor, PrintStream out) {
        this.riskAssessor = riskAssessor;
        this.out = out;
    }

    // ...

}
Kotlin
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.stereotype.Service
import java.io.PrintStream

@Service
class MyAccountService : AccountService {

    private val riskAssessor: RiskAssessor

    private val out: PrintStream

    @Autowired
    constructor(riskAssessor: RiskAssessor) {
        this.riskAssessor = riskAssessor
        out = System.out
    }

    constructor(riskAssessor: RiskAssessor, out: PrintStream) {
        this.riskAssessor = riskAssessor
        this.out = out
    }

    // ...

}
Notice how using constructor injection lets the riskAssessor field be marked as final, indicating that it cannot be subsequently changed.

6.6. Using the @SpringBootApplication Annotation

Many Spring Boot developers like their apps to use auto-configuration, component scan and be able to define extra configuration on their "application class". A single @SpringBootApplication annotation can be used to enable those three features, that is:

  • @EnableAutoConfiguration: enable Spring Boot’s auto-configuration mechanism

  • @ComponentScan: enable @Component scan on the package where the application is located (see the best practices)

  • @SpringBootConfiguration: enable registration of extra beans in the context or the import of additional configuration classes. An alternative to Spring’s standard @Configuration that aids configuration detection in your integration tests.

Java
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

// Same as @SpringBootConfiguration @EnableAutoConfiguration @ComponentScan
@SpringBootApplication
public class MyApplication {

    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }

}
Kotlin
import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

// same as @SpringBootConfiguration @EnableAutoConfiguration @ComponentScan
@SpringBootApplication
class MyApplication

fun main(args: Array<String>) {
    runApplication<MyApplication>(*args)
}
@SpringBootApplication also provides aliases to customize the attributes of @EnableAutoConfiguration and @ComponentScan.

None of these features are mandatory and you may choose to replace this single annotation by any of the features that it enables. For instance, you may not want to use component scan or configuration properties scan in your application:

Java
import org.springframework.boot.SpringApplication;
import org.springframework.boot.SpringBootConfiguration;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.annotation.Import;

@SpringBootConfiguration(proxyBeanMethods = false)
@EnableAutoConfiguration
@Import({ SomeConfiguration.class, AnotherConfiguration.class })
public class MyApplication {

    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }

}
Kotlin
import org.springframework.boot.SpringBootConfiguration
import org.springframework.boot.autoconfigure.EnableAutoConfiguration
import org.springframework.boot.docs.using.structuringyourcode.locatingthemainclass.MyApplication
import org.springframework.boot.runApplication
import org.springframework.context.annotation.Import

@SpringBootConfiguration(proxyBeanMethods = false)
@EnableAutoConfiguration
@Import(SomeConfiguration::class, AnotherConfiguration::class)
class MyApplication

fun main(args: Array<String>) {
    runApplication<MyApplication>(*args)
}

In this example, MyApplication is just like any other Spring Boot application except that @Component-annotated classes and @ConfigurationProperties-annotated classes are not detected automatically and the user-defined beans are imported explicitly (see @Import).

6.7. Running Your Application

One of the biggest advantages of packaging your application as a jar and using an embedded HTTP server is that you can run your application as you would any other. The sample applies to debugging Spring Boot applications. You do not need any special IDE plugins or extensions.

This section only covers jar-based packaging. If you choose to package your application as a war file, see your server and IDE documentation.

6.7.1. Running From an IDE

You can run a Spring Boot application from your IDE as a Java application. However, you first need to import your project. Import steps vary depending on your IDE and build system. Most IDEs can import Maven projects directly. For example, Eclipse users can select Import…​Existing Maven Projects from the File menu.

If you cannot directly import your project into your IDE, you may be able to generate IDE metadata by using a build plugin. Maven includes plugins for Eclipse and IDEA. Gradle offers plugins for various IDEs.

If you accidentally run a web application twice, you see a “Port already in use” error. Spring Tools users can use the Relaunch button rather than the Run button to ensure that any existing instance is closed.

6.7.2. Running as a Packaged Application

If you use the Spring Boot Maven or Gradle plugins to create an executable jar, you can run your application using java -jar, as shown in the following example:

$ java -jar target/myapplication-0.0.1-SNAPSHOT.jar

It is also possible to run a packaged application with remote debugging support enabled. Doing so lets you attach a debugger to your packaged application, as shown in the following example:

$ java -Xdebug -Xrunjdwp:server=y,transport=dt_socket,address=8000,suspend=n \
       -jar target/myapplication-0.0.1-SNAPSHOT.jar

6.7.3. Using the Maven Plugin

The Spring Boot Maven plugin includes a run goal that can be used to quickly compile and run your application. Applications run in an exploded form, as they do in your IDE. The following example shows a typical Maven command to run a Spring Boot application:

$ mvn spring-boot:run

You might also want to use the MAVEN_OPTS operating system environment variable, as shown in the following example:

$ export MAVEN_OPTS=-Xmx1024m

6.7.4. Using the Gradle Plugin

The Spring Boot Gradle plugin also includes a bootRun task that can be used to run your application in an exploded form. The bootRun task is added whenever you apply the org.springframework.boot and java plugins and is shown in the following example:

$ gradle bootRun

You might also want to use the JAVA_OPTS operating system environment variable, as shown in the following example:

$ export JAVA_OPTS=-Xmx1024m

6.7.5. Hot Swapping

Since Spring Boot applications are plain Java applications, JVM hot-swapping should work out of the box. JVM hot swapping is somewhat limited with the bytecode that it can replace. For a more complete solution, JRebel can be used.

The spring-boot-devtools module also includes support for quick application restarts. See the Hot swapping “How-to” for details.

6.8. Developer Tools

Spring Boot includes an additional set of tools that can make the application development experience a little more pleasant. The spring-boot-devtools module can be included in any project to provide additional development-time features. To include devtools support, add the module dependency to your build, as shown in the following listings for Maven and Gradle:

Maven
<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-devtools</artifactId>
        <optional>true</optional>
    </dependency>
</dependencies>
Gradle
dependencies {
    developmentOnly("org.springframework.boot:spring-boot-devtools")
}
Devtools might cause classloading issues, in particular in multi-module projects. Diagnosing Classloading Issues explains how to diagnose and solve them.
Developer tools are automatically disabled when running a fully packaged application. If your application is launched from java -jar or if it is started from a special classloader, then it is considered a “production application”. You can control this behavior by using the spring.devtools.restart.enabled system property. To enable devtools, irrespective of the classloader used to launch your application, set the -Dspring.devtools.restart.enabled=true system property. This must not be done in a production environment where running devtools is a security risk. To disable devtools, exclude the dependency or set the -Dspring.devtools.restart.enabled=false system property.
Flagging the dependency as optional in Maven or using the developmentOnly configuration in Gradle (as shown above) prevents devtools from being transitively applied to other modules that use your project.
Repackaged archives do not contain devtools by default. If you want to use a certain remote devtools feature, you need to include it. When using the Maven plugin, set the excludeDevtools property to false. When using the Gradle plugin, configure the task’s classpath to include the developmentOnly configuration.

6.8.1. Diagnosing Classloading Issues

As described in the Restart vs Reload section, restart functionality is implemented by using two classloaders. For most applications, this approach works well. However, it can sometimes cause classloading issues, in particular in multi-module projects.

To diagnose whether the classloading issues are indeed caused by devtools and its two classloaders, try disabling restart. If this solves your problems, customize the restart classloader to include your entire project.

6.8.2. Property Defaults

Several of the libraries supported by Spring Boot use caches to improve performance. For example, template engines cache compiled templates to avoid repeatedly parsing template files. Also, Spring MVC can add HTTP caching headers to responses when serving static resources.

While caching is very beneficial in production, it can be counter-productive during development, preventing you from seeing the changes you just made in your application. For this reason, spring-boot-devtools disables the caching options by default.

Cache options are usually configured by settings in your application.properties file. For example, Thymeleaf offers the spring.thymeleaf.cache property. Rather than needing to set these properties manually, the spring-boot-devtools module automatically applies sensible development-time configuration.

The following table lists all the properties that are applied:

Name Default Value

server.error.include-binding-errors

always

server.error.include-message

always

server.error.include-stacktrace

always

server.servlet.jsp.init-parameters.development

true

server.servlet.session.persistent

true

spring.freemarker.cache

false

spring.graphql.graphiql.enabled

true

spring.groovy.template.cache

false

spring.h2.console.enabled

true

spring.mustache.servlet.cache

false

spring.mvc.log-resolved-exception

true

spring.reactor.netty.shutdown-quiet-period

0s

spring.template.provider.cache

false

spring.thymeleaf.cache

false

spring.web.resources.cache.period

0

spring.web.resources.chain.cache

false

If you do not want property defaults to be applied you can set spring.devtools.add-properties to false in your application.properties.

Because you need more information about web requests while developing Spring MVC and Spring WebFlux applications, developer tools suggests you to enable DEBUG logging for the web logging group. This will give you information about the incoming request, which handler is processing it, the response outcome, and other details. If you wish to log all request details (including potentially sensitive information), you can turn on the spring.mvc.log-request-details or spring.codec.log-request-details configuration properties.

6.8.3. Automatic Restart

Applications that use spring-boot-devtools automatically restart whenever files on the classpath change. This can be a useful feature when working in an IDE, as it gives a very fast feedback loop for code changes. By default, any entry on the classpath that points to a directory is monitored for changes. Note that certain resources, such as static assets and view templates, do not need to restart the application.

Triggering a restart

As DevTools monitors classpath resources, the only way to trigger a restart is to update the classpath. Whether you’re using an IDE or one of the build plugins, the modified files have to be recompiled to trigger a restart. The way in which you cause the classpath to be updated depends on the tool that you are using:

  • In Eclipse, saving a modified file causes the classpath to be updated and triggers a restart.

  • In IntelliJ IDEA, building the project (Build +→+ Build Project) has the same effect.

  • If using a build plugin, running mvn compile for Maven or gradle build for Gradle will trigger a restart.

If you are restarting with Maven or Gradle using the build plugin you must leave the forking set to enabled. If you disable forking, the isolated application classloader used by devtools will not be created and restarts will not operate properly.
Automatic restart works very well when used with LiveReload. See the LiveReload section for details. If you use JRebel, automatic restarts are disabled in favor of dynamic class reloading. Other devtools features (such as LiveReload and property overrides) can still be used.
DevTools relies on the application context’s shutdown hook to close it during a restart. It does not work correctly if you have disabled the shutdown hook (SpringApplication.setRegisterShutdownHook(false)).
DevTools needs to customize the ResourceLoader used by the ApplicationContext. If your application provides one already, it is going to be wrapped. Direct override of the getResource method on the ApplicationContext is not supported.
Automatic restart is not supported when using AspectJ weaving.
Restart vs Reload

The restart technology provided by Spring Boot works by using two classloaders. Classes that do not change (for example, those from third-party jars) are loaded into a base classloader. Classes that you are actively developing are loaded into a restart classloader. When the application is restarted, the restart classloader is thrown away and a new one is created. This approach means that application restarts are typically much faster than “cold starts”, since the base classloader is already available and populated.

If you find that restarts are not quick enough for your applications or you encounter classloading issues, you could consider reloading technologies such as JRebel from ZeroTurnaround. These work by rewriting classes as they are loaded to make them more amenable to reloading.

Logging Changes in Condition Evaluation

By default, each time your application restarts, a report showing the condition evaluation delta is logged. The report shows the changes to your application’s auto-configuration as you make changes such as adding or removing beans and setting configuration properties.

To disable the logging of the report, set the following property:

Properties
spring.devtools.restart.log-condition-evaluation-delta=false
Yaml
spring:
  devtools:
    restart:
      log-condition-evaluation-delta: false
Excluding Resources

Certain resources do not necessarily need to trigger a restart when they are changed. For example, Thymeleaf templates can be edited in-place. By default, changing resources in /META-INF/maven, /META-INF/resources, /resources, /static, /public, or /templates does not trigger a restart but does trigger a live reload. If you want to customize these exclusions, you can use the spring.devtools.restart.exclude property. For example, to exclude only /static and /public you would set the following property:

Properties
spring.devtools.restart.exclude=static/**,public/**
Yaml
spring:
  devtools:
    restart:
      exclude: "static/**,public/**"
If you want to keep those defaults and add additional exclusions, use the spring.devtools.restart.additional-exclude property instead.
Watching Additional Paths

You may want your application to be restarted or reloaded when you make changes to files that are not on the classpath. To do so, use the spring.devtools.restart.additional-paths property to configure additional paths to watch for changes. You can use the spring.devtools.restart.exclude property described earlier to control whether changes beneath the additional paths trigger a full restart or a live reload.

Disabling Restart

If you do not want to use the restart feature, you can disable it by using the spring.devtools.restart.enabled property. In most cases, you can set this property in your application.properties (doing so still initializes the restart classloader, but it does not watch for file changes).

If you need to completely disable restart support (for example, because it does not work with a specific library), you need to set the spring.devtools.restart.enabled System property to false before calling SpringApplication.run(…​), as shown in the following example:

Java
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MyApplication {

    public static void main(String[] args) {
        System.setProperty("spring.devtools.restart.enabled", "false");
        SpringApplication.run(MyApplication.class, args);
    }

}
Kotlin
import org.springframework.boot.SpringApplication
import org.springframework.boot.autoconfigure.SpringBootApplication

@SpringBootApplication
object MyApplication {

    @JvmStatic
    fun main(args: Array<String>) {
        System.setProperty("spring.devtools.restart.enabled", "false")
        SpringApplication.run(MyApplication::class.java, *args)
    }

}
Using a Trigger File

If you work with an IDE that continuously compiles changed files, you might prefer to trigger restarts only at specific times. To do so, you can use a “trigger file”, which is a special file that must be modified when you want to actually trigger a restart check.

Any update to the file will trigger a check, but restart only actually occurs if Devtools has detected it has something to do.

To use a trigger file, set the spring.devtools.restart.trigger-file property to the name (excluding any path) of your trigger file. The trigger file must appear somewhere on your classpath.

For example, if you have a project with the following structure:

src
+- main
   +- resources
      +- .reloadtrigger

Then your trigger-file property would be:

Properties
spring.devtools.restart.trigger-file=.reloadtrigger
Yaml
spring:
  devtools:
    restart:
      trigger-file: ".reloadtrigger"

Restarts will now only happen when the src/main/resources/.reloadtrigger is updated.

You might want to set spring.devtools.restart.trigger-file as a global setting, so that all your projects behave in the same way.

Some IDEs have features that save you from needing to update your trigger file manually. Spring Tools for Eclipse and IntelliJ IDEA (Ultimate Edition) both have such support. With Spring Tools, you can use the “reload” button from the console view (as long as your trigger-file is named .reloadtrigger). For IntelliJ IDEA, you can follow the instructions in their documentation.

Customizing the Restart Classloader

As described earlier in the Restart vs Reload section, restart functionality is implemented by using two classloaders. If this causes issues, you might need to customize what gets loaded by which classloader.

By default, any open project in your IDE is loaded with the “restart” classloader, and any regular .jar file is loaded with the “base” classloader. The same is true if you use mvn spring-boot:run or gradle bootRun: the project containing your @SpringBootApplication is loaded with the “restart” classloader, and everything else with the “base” classloader.

You can instruct Spring Boot to load parts of your project with a different classloader by creating a META-INF/spring-devtools.properties file. The spring-devtools.properties file can contain properties prefixed with restart.exclude and restart.include. The include elements are items that should be pulled up into the “restart” classloader, and the exclude elements are items that should be pushed down into the “base” classloader. The value of the property is a regex pattern that is applied to the classpath, as shown in the following example:

Properties
restart.exclude.companycommonlibs=/mycorp-common-[\\w\\d-\\.]+\\.jar
restart.include.projectcommon=/mycorp-myproj-[\\w\\d-\\.]+\\.jar
Yaml
restart:
  exclude:
    companycommonlibs: "/mycorp-common-[\\w\\d-\\.]+\\.jar"
  include:
    projectcommon: "/mycorp-myproj-[\\w\\d-\\.]+\\.jar"
All property keys must be unique. As long as a property starts with restart.include. or restart.exclude. it is considered.
All META-INF/spring-devtools.properties from the classpath are loaded. You can package files inside your project, or in the libraries that the project consumes.
Known Limitations

Restart functionality does not work well with objects that are deserialized by using a standard ObjectInputStream. If you need to deserialize data, you may need to use Spring’s ConfigurableObjectInputStream in combination with Thread.currentThread().getContextClassLoader().

Unfortunately, several third-party libraries deserialize without considering the context classloader. If you find such a problem, you need to request a fix with the original authors.

6.8.4. LiveReload

The spring-boot-devtools module includes an embedded LiveReload server that can be used to trigger a browser refresh when a resource is changed. LiveReload browser extensions are freely available for Chrome, Firefox and Safari. You can find these extensions by searching 'LiveReload' in the marketplace or store of your chosen browser.

If you do not want to start the LiveReload server when your application runs, you can set the spring.devtools.livereload.enabled property to false.

You can only run one LiveReload server at a time. Before starting your application, ensure that no other LiveReload servers are running. If you start multiple applications from your IDE, only the first has LiveReload support.
To trigger LiveReload when a file changes, Automatic Restart must be enabled.

6.8.5. Global Settings

You can configure global devtools settings by adding any of the following files to the $HOME/.config/spring-boot directory:

  1. spring-boot-devtools.properties

  2. spring-boot-devtools.yaml

  3. spring-boot-devtools.yml

Any properties added to these files apply to all Spring Boot applications on your machine that use devtools. For example, to configure restart to always use a trigger file, you would add the following property to your spring-boot-devtools file:

Properties
spring.devtools.restart.trigger-file=.reloadtrigger
Yaml
spring:
  devtools:
    restart:
      trigger-file: ".reloadtrigger"

By default, $HOME is the user’s home directory. To customize this location, set the SPRING_DEVTOOLS_HOME environment variable or the spring.devtools.home system property.

If devtools configuration files are not found in $HOME/.config/spring-boot, the root of the $HOME directory is searched for the presence of a .spring-boot-devtools.properties file. This allows you to share the devtools global configuration with applications that are on an older version of Spring Boot that does not support the $HOME/.config/spring-boot location.

Profiles are not supported in devtools properties/yaml files.

Any profiles activated in .spring-boot-devtools.properties will not affect the loading of profile-specific configuration files. Profile specific filenames (of the form spring-boot-devtools-<profile>.properties) and spring.config.activate.on-profile documents in both YAML and Properties files are not supported.

Configuring File System Watcher

FileSystemWatcher works by polling the class changes with a certain time interval, and then waiting for a predefined quiet period to make sure there are no more changes. Since Spring Boot relies entirely on the IDE to compile and copy files into the location from where Spring Boot can read them, you might find that there are times when certain changes are not reflected when devtools restarts the application. If you observe such problems constantly, try increasing the spring.devtools.restart.poll-interval and spring.devtools.restart.quiet-period parameters to the values that fit your development environment:

Properties
spring.devtools.restart.poll-interval=2s
spring.devtools.restart.quiet-period=1s
Yaml
spring:
  devtools:
    restart:
      poll-interval: "2s"
      quiet-period: "1s"

The monitored classpath directories are now polled every 2 seconds for changes, and a 1 second quiet period is maintained to make sure there are no additional class changes.

6.8.6. Remote Applications

The Spring Boot developer tools are not limited to local development. You can also use several features when running applications remotely. Remote support is opt-in as enabling it can be a security risk. It should only be enabled when running on a trusted network or when secured with SSL. If neither of these options is available to you, you should not use DevTools' remote support. You should never enable support on a production deployment.

To enable it, you need to make sure that devtools is included in the repackaged archive, as shown in the following listing:

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <configuration>
                <excludeDevtools>false</excludeDevtools>
            </configuration>
        </plugin>
    </plugins>
</build>

Then you need to set the spring.devtools.remote.secret property. Like any important password or secret, the value should be unique and strong such that it cannot be guessed or brute-forced.

Remote devtools support is provided in two parts: a server-side endpoint that accepts connections and a client application that you run in your IDE. The server component is automatically enabled when the spring.devtools.remote.secret property is set. The client component must be launched manually.

Remote devtools is not supported for Spring WebFlux applications.
Running the Remote Client Application

The remote client application is designed to be run from within your IDE. You need to run org.springframework.boot.devtools.RemoteSpringApplication with the same classpath as the remote project that you connect to. The application’s single required argument is the remote URL to which it connects.

For example, if you are using Eclipse or Spring Tools and you have a project named my-app that you have deployed to Cloud Foundry, you would do the following:

  • Select Run Configurations…​ from the Run menu.

  • Create a new Java Application “launch configuration”.

  • Browse for the my-app project.

  • Use org.springframework.boot.devtools.RemoteSpringApplication as the main class.

  • Add https://myapp.cfapps.io to the Program arguments (or whatever your remote URL is).

A running remote client might resemble the following listing:

  .   ____          _                                              __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _          ___               _      \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` |        | _ \___ _ __  ___| |_ ___ \ \ \ \
 \\/  ___)| |_)| | | | | || (_| []::::::[]   / -_) '  \/ _ \  _/ -_) ) ) ) )
  '  |____| .__|_| |_|_| |_\__, |        |_|_\___|_|_|_\___/\__\___|/ / / /
 =========|_|==============|___/===================================/_/_/_/
 :: Spring Boot Remote ::  (v2.7.18)

2023-11-23 07:23:21.930  INFO 28462 --- [           main] o.s.b.devtools.RemoteSpringApplication   : Starting RemoteSpringApplication v2.7.18 using Java 1.8.0_392 on myhost with PID 28462 (/Users/myuser/.m2/repository/org/springframework/boot/spring-boot-devtools/2.7.18/spring-boot-devtools-2.7.18.jar started by myuser in /opt/apps/)
2023-11-23 07:23:21.936  INFO 28462 --- [           main] o.s.b.devtools.RemoteSpringApplication   : No active profile set, falling back to 1 default profile: "default"
2023-11-23 07:23:22.314  INFO 28462 --- [           main] o.s.b.d.a.OptionalLiveReloadServer       : LiveReload server is running on port 35729
2023-11-23 07:23:22.338  INFO 28462 --- [           main] o.s.b.devtools.RemoteSpringApplication   : Started RemoteSpringApplication in 0.858 seconds (JVM running for 1.35)
Because the remote client is using the same classpath as the real application it can directly read application properties. This is how the spring.devtools.remote.secret property is read and passed to the server for authentication.
It is always advisable to use https:// as the connection protocol, so that traffic is encrypted and passwords cannot be intercepted.
If you need to use a proxy to access the remote application, configure the spring.devtools.remote.proxy.host and spring.devtools.remote.proxy.port properties.
Remote Update

The remote client monitors your application classpath for changes in the same way as the local restart. Any updated resource is pushed to the remote application and (if required) triggers a restart. This can be helpful if you iterate on a feature that uses a cloud service that you do not have locally. Generally, remote updates and restarts are much quicker than a full rebuild and deploy cycle.

On a slower development environment, it may happen that the quiet period is not enough, and the changes in the classes may be split into batches. The server is restarted after the first batch of class changes is uploaded. The next batch can’t be sent to the application, since the server is restarting.

This is typically manifested by a warning in the RemoteSpringApplication logs about failing to upload some of the classes, and a consequent retry. But it may also lead to application code inconsistency and failure to restart after the first batch of changes is uploaded. If you observe such problems constantly, try increasing the spring.devtools.restart.poll-interval and spring.devtools.restart.quiet-period parameters to the values that fit your development environment. See the Configuring File System Watcher section for configuring these properties.

Files are only monitored when the remote client is running. If you change a file before starting the remote client, it is not pushed to the remote server.

6.9. Packaging Your Application for Production

Executable jars can be used for production deployment. As they are self-contained, they are also ideally suited for cloud-based deployment.

For additional “production ready” features, such as health, auditing, and metric REST or JMX end-points, consider adding spring-boot-actuator. See Production-ready Features for details.

6.10. What to Read Next

You should now understand how you can use Spring Boot and some best practices that you should follow. You can now go on to learn about specific Spring Boot features in depth, or you could skip ahead and read about the “production ready” aspects of Spring Boot.

7. Core Features

This section dives into the details of Spring Boot. Here you can learn about the key features that you may want to use and customize. If you have not already done so, you might want to read the "Getting Started" and "Developing with Spring Boot" sections, so that you have a good grounding of the basics.

7.1. SpringApplication

The SpringApplication class provides a convenient way to bootstrap a Spring application that is started from a main() method. In many situations, you can delegate to the static SpringApplication.run method, as shown in the following example:

Java
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MyApplication {

    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }

}
Kotlin
import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication


@SpringBootApplication
class MyApplication

fun main(args: Array<String>) {
    runApplication<MyApplication>(*args)
}

When your application starts, you should see something similar to the following output:

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::               (v2.7.18)

2023-11-23 07:23:23.238  INFO 28579 --- [           main] o.s.b.d.f.logexample.MyApplication       : Starting MyApplication using Java 1.8.0_392 on myhost with PID 28579 (/opt/apps/myapp.jar started by myuser in /opt/apps/)
2023-11-23 07:23:23.245  INFO 28579 --- [           main] o.s.b.d.f.logexample.MyApplication       : No active profile set, falling back to 1 default profile: "default"
2023-11-23 07:23:24.552  INFO 28579 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2023-11-23 07:23:24.567  INFO 28579 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2023-11-23 07:23:24.567  INFO 28579 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.83]
2023-11-23 07:23:24.658  INFO 28579 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2023-11-23 07:23:24.659  INFO 28579 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1346 ms
2023-11-23 07:23:25.336  INFO 28579 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2023-11-23 07:23:25.355  INFO 28579 --- [           main] o.s.b.d.f.logexample.MyApplication       : Started MyApplication in 2.63 seconds (JVM running for 3.003)

By default, INFO logging messages are shown, including some relevant startup details, such as the user that launched the application. If you need a log level other than INFO, you can set it, as described in Log Levels. The application version is determined using the implementation version from the main application class’s package. Startup information logging can be turned off by setting spring.main.log-startup-info to false. This will also turn off logging of the application’s active profiles.

To add additional logging during startup, you can override logStartupInfo(boolean) in a subclass of SpringApplication.

7.1.1. Startup Failure

If your application fails to start, registered FailureAnalyzers get a chance to provide a dedicated error message and a concrete action to fix the problem. For instance, if you start a web application on port 8080 and that port is already in use, you should see something similar to the following message:

***************************
APPLICATION FAILED TO START
***************************

Description:

Embedded servlet container failed to start. Port 8080 was already in use.

Action:

Identify and stop the process that is listening on port 8080 or configure this application to listen on another port.
Spring Boot provides numerous FailureAnalyzer implementations, and you can add your own.

If no failure analyzers are able to handle the exception, you can still display the full conditions report to better understand what went wrong. To do so, you need to enable the debug property or enable DEBUG logging for org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener.

For instance, if you are running your application by using java -jar, you can enable the debug property as follows:

$ java -jar myproject-0.0.1-SNAPSHOT.jar --debug

7.1.2. Lazy Initialization

SpringApplication allows an application to be initialized lazily. When lazy initialization is enabled, beans are created as they are needed rather than during application startup. As a result, enabling lazy initialization can reduce the time that it takes your application to start. In a web application, enabling lazy initialization will result in many web-related beans not being initialized until an HTTP request is received.

A downside of lazy initialization is that it can delay the discovery of a problem with the application. If a misconfigured bean is initialized lazily, a failure will no longer occur during startup and the problem will only become apparent when the bean is initialized. Care must also be taken to ensure that the JVM has sufficient memory to accommodate all of the application’s beans and not just those that are initialized during startup. For these reasons, lazy initialization is not enabled by default and it is recommended that fine-tuning of the JVM’s heap size is done before enabling lazy initialization.

Lazy initialization can be enabled programmatically using the lazyInitialization method on SpringApplicationBuilder or the setLazyInitialization method on SpringApplication. Alternatively, it can be enabled using the spring.main.lazy-initialization property as shown in the following example:

Properties
spring.main.lazy-initialization=true
Yaml
spring:
  main:
    lazy-initialization: true
If you want to disable lazy initialization for certain beans while using lazy initialization for the rest of the application, you can explicitly set their lazy attribute to false using the @Lazy(false) annotation.

7.1.3. Customizing the Banner

The banner that is printed on start up can be changed by adding a banner.txt file to your classpath or by setting the spring.banner.location property to the location of such a file. If the file has an encoding other than UTF-8, you can set spring.banner.charset. In addition to a text file, you can also add a banner.gif, banner.jpg, or banner.png image file to your classpath or set the spring.banner.image.location property. Images are converted into an ASCII art representation and printed above any text banner.

Inside your banner.txt file, you can use any key available in the Environment as well as any of the following placeholders:

Table 4. Banner variables
Variable Description

${application.version}

The version number of your application, as declared in MANIFEST.MF. For example, Implementation-Version: 1.0 is printed as 1.0.

${application.formatted-version}

The version number of your application, as declared in MANIFEST.MF and formatted for display (surrounded with brackets and prefixed with v). For example (v1.0).

${spring-boot.version}

The Spring Boot version that you are using. For example 2.7.18.

${spring-boot.formatted-version}

The Spring Boot version that you are using, formatted for display (surrounded with brackets and prefixed with v). For example (v2.7.18).

${Ansi.NAME} (or ${AnsiColor.NAME}, ${AnsiBackground.NAME}, ${AnsiStyle.NAME})

Where NAME is the name of an ANSI escape code. See AnsiPropertySource for details.

${application.title}

The title of your application, as declared in MANIFEST.MF. For example Implementation-Title: MyApp is printed as MyApp.

The SpringApplication.setBanner(…​) method can be used if you want to generate a banner programmatically. Use the org.springframework.boot.Banner interface and implement your own printBanner() method.

You can also use the spring.main.banner-mode property to determine if the banner has to be printed on System.out (console), sent to the configured logger (log), or not produced at all (off).

The printed banner is registered as a singleton bean under the following name: springBootBanner.

The application.title, application.version, and application.formatted-version properties are only available if you are using java -jar or java -cp with Spring Boot launchers. The values will not be resolved if you are running an unpacked jar and starting it with java -cp <classpath> <mainclass>.

To use the application. properties, launch your application as a packed jar using java -jar or as an unpacked jar using java org.springframework.boot.loader.JarLauncher. This will initialize the application. banner properties before building the classpath and launching your app.

7.1.4. Customizing SpringApplication

If the SpringApplication defaults are not to your taste, you can instead create a local instance and customize it. For example, to turn off the banner, you could write:

Java
import org.springframework.boot.Banner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MyApplication {

    public static void main(String[] args) {
        SpringApplication application = new SpringApplication(MyApplication.class);
        application.setBannerMode(Banner.Mode.OFF);
        application.run(args);
    }

}
Kotlin
import org.springframework.boot.Banner
import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class MyApplication

fun main(args: Array<String>) {
    runApplication<MyApplication>(*args) {
        setBannerMode(Banner.Mode.OFF)
    }
}
The constructor arguments passed to SpringApplication are configuration sources for Spring beans. In most cases, these are references to @Configuration classes, but they could also be direct references @Component classes.

It is also possible to configure the SpringApplication by using an application.properties file. See Externalized Configuration for details.

For a complete list of the configuration options, see the SpringApplication Javadoc.

7.1.5. Fluent Builder API

If you need to build an ApplicationContext hierarchy (multiple contexts with a parent/child relationship) or if you prefer using a “fluent” builder API, you can use the SpringApplicationBuilder.

The SpringApplicationBuilder lets you chain together multiple method calls and includes parent and child methods that let you create a hierarchy, as shown in the following example:

Java
new SpringApplicationBuilder()
        .sources(Parent.class)
        .child(Application.class)
        .bannerMode(Banner.Mode.OFF)
        .run(args);
Kotlin
SpringApplicationBuilder()
    .sources(Parent::class.java)
    .child(Application::class.java)
    .bannerMode(Banner.Mode.OFF)
    .run(*args)
There are some restrictions when creating an ApplicationContext hierarchy. For example, Web components must be contained within the child context, and the same Environment is used for both parent and child contexts. See the SpringApplicationBuilder Javadoc for full details.

7.1.6. Application Availability

When deployed on platforms, applications can provide information about their availability to the platform using infrastructure such as Kubernetes Probes. Spring Boot includes out-of-the box support for the commonly used “liveness” and “readiness” availability states. If you are using Spring Boot’s “actuator” support then these states are exposed as health endpoint groups.

In addition, you can also obtain availability states by injecting the ApplicationAvailability interface into your own beans.

Liveness State

The “Liveness” state of an application tells whether its internal state allows it to work correctly, or recover by itself if it is currently failing. A broken “Liveness” state means that the application is in a state that it cannot recover from, and the infrastructure should restart the application.

In general, the "Liveness" state should not be based on external checks, such as Health checks. If it did, a failing external system (a database, a Web API, an external cache) would trigger massive restarts and cascading failures across the platform.

The internal state of Spring Boot applications is mostly represented by the Spring ApplicationContext. If the application context has started successfully, Spring Boot assumes that the application is in a valid state. An application is considered live as soon as the context has been refreshed, see Spring Boot application lifecycle and related Application Events.

Readiness State

The “Readiness” state of an application tells whether the application is ready to handle traffic. A failing “Readiness” state tells the platform that it should not route traffic to the application for now. This typically happens during startup, while CommandLineRunner and ApplicationRunner components are being processed, or at any time if the application decides that it is too busy for additional traffic.

An application is considered ready as soon as application and command-line runners have been called, see Spring Boot application lifecycle and related Application Events.

Tasks expected to run during startup should be executed by CommandLineRunner and ApplicationRunner components instead of using Spring component lifecycle callbacks such as @PostConstruct.
Managing the Application Availability State

Application components can retrieve the current availability state at any time, by injecting the ApplicationAvailability interface and calling methods on it. More often, applications will want to listen to state updates or update the state of the application.

For example, we can export the "Readiness" state of the application to a file so that a Kubernetes "exec Probe" can look at this file:

Java
import org.springframework.boot.availability.AvailabilityChangeEvent;
import org.springframework.boot.availability.ReadinessState;
import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;

@Component
public class MyReadinessStateExporter {

    @EventListener
    public void onStateChange(AvailabilityChangeEvent<ReadinessState> event) {
        switch (event.getState()) {
            case ACCEPTING_TRAFFIC:
                // create file /tmp/healthy
                break;
            case REFUSING_TRAFFIC:
                // remove file /tmp/healthy
                break;
        }
    }

}
Kotlin
import org.springframework.boot.availability.AvailabilityChangeEvent
import org.springframework.boot.availability.ReadinessState
import org.springframework.context.event.EventListener
import org.springframework.stereotype.Component

@Component
class MyReadinessStateExporter {

    @EventListener
    fun onStateChange(event: AvailabilityChangeEvent<ReadinessState?>) {
        when (event.state) {
            ReadinessState.ACCEPTING_TRAFFIC -> {
                // create file /tmp/healthy
            }
            ReadinessState.REFUSING_TRAFFIC -> {
                // remove file /tmp/healthy
            }
            else -> {
                // ...
            }
        }
    }

}

We can also update the state of the application, when the application breaks and cannot recover:

Java
import org.springframework.boot.availability.AvailabilityChangeEvent;
import org.springframework.boot.availability.LivenessState;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.stereotype.Component;

@Component
public class MyLocalCacheVerifier {

    private final ApplicationEventPublisher eventPublisher;

    public MyLocalCacheVerifier(ApplicationEventPublisher eventPublisher) {
        this.eventPublisher = eventPublisher;
    }

    public void checkLocalCache() {
        try {
            // ...
        }
        catch (CacheCompletelyBrokenException ex) {
            AvailabilityChangeEvent.publish(this.eventPublisher, ex, LivenessState.BROKEN);
        }
    }

}
Kotlin
import org.springframework.boot.availability.AvailabilityChangeEvent
import org.springframework.boot.availability.LivenessState
import org.springframework.context.ApplicationEventPublisher
import org.springframework.stereotype.Component

@Component
class MyLocalCacheVerifier(private val eventPublisher: ApplicationEventPublisher) {

    fun checkLocalCache() {
        try {
            // ...
        } catch (ex: CacheCompletelyBrokenException) {
            AvailabilityChangeEvent.publish(eventPublisher, ex, LivenessState.BROKEN)
        }
    }

}

7.1.7. Application Events and Listeners

In addition to the usual Spring Framework events, such as ContextRefreshedEvent, a SpringApplication sends some additional application events.

Some events are actually triggered before the ApplicationContext is created, so you cannot register a listener on those as a @Bean. You can register them with the SpringApplication.addListeners(…​) method or the SpringApplicationBuilder.listeners(…​) method.

If you want those listeners to be registered automatically, regardless of the way the application is created, you can add a META-INF/spring.factories file to your project and reference your listener(s) by using the org.springframework.context.ApplicationListener key, as shown in the following example:

org.springframework.context.ApplicationListener=com.example.project.MyListener

Application events are sent in the following order, as your application runs:

  1. An ApplicationStartingEvent is sent at the start of a run but before any processing, except for the registration of listeners and initializers.

  2. An ApplicationEnvironmentPreparedEvent is sent when the Environment to be used in the context is known but before the context is created.

  3. An ApplicationContextInitializedEvent is sent when the ApplicationContext is prepared and ApplicationContextInitializers have been called but before any bean definitions are loaded.

  4. An ApplicationPreparedEvent is sent just before the refresh is started but after bean definitions have been loaded.

  5. An ApplicationStartedEvent is sent after the context has been refreshed but before any application and command-line runners have been called.

  6. An AvailabilityChangeEvent is sent right after with LivenessState.CORRECT to indicate that the application is considered as live.

  7. An ApplicationReadyEvent is sent after any application and command-line runners have been called.

  8. An AvailabilityChangeEvent is sent right after with ReadinessState.ACCEPTING_TRAFFIC to indicate that the application is ready to service requests.

  9. An ApplicationFailedEvent is sent if there is an exception on startup.

The above list only includes SpringApplicationEvents that are tied to a SpringApplication. In addition to these, the following events are also published after ApplicationPreparedEvent and before ApplicationStartedEvent:

  • A WebServerInitializedEvent is sent after the WebServer is ready. ServletWebServerInitializedEvent and ReactiveWebServerInitializedEvent are the servlet and reactive variants respectively.

  • A ContextRefreshedEvent is sent when an ApplicationContext is refreshed.

You often need not use application events, but it can be handy to know that they exist. Internally, Spring Boot uses events to handle a variety of tasks.
Event listeners should not run potentially lengthy tasks as they execute in the same thread by default. Consider using application and command-line runners instead.

Application events are sent by using Spring Framework’s event publishing mechanism. Part of this mechanism ensures that an event published to the listeners in a child context is also published to the listeners in any ancestor contexts. As a result of this, if your application uses a hierarchy of SpringApplication instances, a listener may receive multiple instances of the same type of application event.

To allow your listener to distinguish between an event for its context and an event for a descendant context, it should request that its application context is injected and then compare the injected context with the context of the event. The context can be injected by implementing ApplicationContextAware or, if the listener is a bean, by using @Autowired.

7.1.8. Web Environment

A SpringApplication attempts to create the right type of ApplicationContext on your behalf. The algorithm used to determine a WebApplicationType is the following:

  • If Spring MVC is present, an AnnotationConfigServletWebServerApplicationContext is used

  • If Spring MVC is not present and Spring WebFlux is present, an AnnotationConfigReactiveWebServerApplicationContext is used

  • Otherwise, AnnotationConfigApplicationContext is used

This means that if you are using Spring MVC and the new WebClient from Spring WebFlux in the same application, Spring MVC will be used by default. You can override that easily by calling setWebApplicationType(WebApplicationType).

It is also possible to take complete control of the ApplicationContext type that is used by calling setApplicationContextFactory(…​).

It is often desirable to call setWebApplicationType(WebApplicationType.NONE) when using SpringApplication within a JUnit test.

7.1.9. Accessing Application Arguments

If you need to access the application arguments that were passed to SpringApplication.run(…​), you can inject a org.springframework.boot.ApplicationArguments bean. The ApplicationArguments interface provides access to both the raw String[] arguments as well as parsed option and non-option arguments, as shown in the following example:

Java
import java.util.List;

import org.springframework.boot.ApplicationArguments;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

    public MyBean(ApplicationArguments args) {
        boolean debug = args.containsOption("debug");
        List<String> files = args.getNonOptionArgs();
        if (debug) {
            System.out.println(files);
        }
        // if run with "--debug logfile.txt" prints ["logfile.txt"]
    }

}
Kotlin
import org.springframework.boot.ApplicationArguments
import org.springframework.stereotype.Component

@Component
class MyBean(args: ApplicationArguments) {

    init {
        val debug = args.containsOption("debug")
        val files = args.nonOptionArgs
        if (debug) {
            println(files)
        }
        // if run with "--debug logfile.txt" prints ["logfile.txt"]
    }

}
Spring Boot also registers a CommandLinePropertySource with the Spring Environment. This lets you also inject single application arguments by using the @Value annotation.

7.1.10. Using the ApplicationRunner or CommandLineRunner

If you need to run some specific code once the SpringApplication has started, you can implement the ApplicationRunner or CommandLineRunner interfaces. Both interfaces work in the same way and offer a single run method, which is called just before SpringApplication.run(…​) completes.

This contract is well suited for tasks that should run after application startup but before it starts accepting traffic.

The CommandLineRunner interfaces provides access to application arguments as a string array, whereas the ApplicationRunner uses the ApplicationArguments interface discussed earlier. The following example shows a CommandLineRunner with a run method:

Java
import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;

@Component
public class MyCommandLineRunner implements CommandLineRunner {

    @Override
    public void run(String... args) {
        // Do something...
    }

}
Kotlin
import org.springframework.boot.CommandLineRunner
import org.springframework.stereotype.Component

@Component
class MyCommandLineRunner : CommandLineRunner {

    override fun run(vararg args: String) {
        // Do something...
    }

}

If several CommandLineRunner or ApplicationRunner beans are defined that must be called in a specific order, you can additionally implement the org.springframework.core.Ordered interface or use the org.springframework.core.annotation.Order annotation.

7.1.11. Application Exit

Each SpringApplication registers a shutdown hook with the JVM to ensure that the ApplicationContext closes gracefully on exit. All the standard Spring lifecycle callbacks (such as the DisposableBean interface or the @PreDestroy annotation) can be used.

In addition, beans may implement the org.springframework.boot.ExitCodeGenerator interface if they wish to return a specific exit code when SpringApplication.exit() is called. This exit code can then be passed to System.exit() to return it as a status code, as shown in the following example:

Java
import org.springframework.boot.ExitCodeGenerator;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
public class MyApplication {

    @Bean
    public ExitCodeGenerator exitCodeGenerator() {
        return () -> 42;
    }

    public static void main(String[] args) {
        System.exit(SpringApplication.exit(SpringApplication.run(MyApplication.class, args)));
    }

}
Kotlin
import org.springframework.boot.ExitCodeGenerator
import org.springframework.boot.SpringApplication
import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication
import org.springframework.context.annotation.Bean

import kotlin.system.exitProcess

@SpringBootApplication
class MyApplication {

    @Bean
    fun exitCodeGenerator() = ExitCodeGenerator { 42 }

}

fun main(args: Array<String>) {
    exitProcess(SpringApplication.exit(
        runApplication<MyApplication>(*args)))
}

Also, the ExitCodeGenerator interface may be implemented by exceptions. When such an exception is encountered, Spring Boot returns the exit code provided by the implemented getExitCode() method.

If there is more than one ExitCodeGenerator, the first non-zero exit code that is generated is used. To control the order in which the generators are called, additionally implement the org.springframework.core.Ordered interface or use the org.springframework.core.annotation.Order annotation.

7.1.12. Admin Features

It is possible to enable admin-related features for the application by specifying the spring.application.admin.enabled property. This exposes the SpringApplicationAdminMXBean on the platform MBeanServer. You could use this feature to administer your Spring Boot application remotely. This feature could also be useful for any service wrapper implementation.

If you want to know on which HTTP port the application is running, get the property with a key of local.server.port.

7.1.13. Application Startup tracking

During the application startup, the SpringApplication and the ApplicationContext perform many tasks related to the application lifecycle, the beans lifecycle or even processing application events. With ApplicationStartup, Spring Framework allows you to track the application startup sequence with StartupStep objects. This data can be collected for profiling purposes, or just to have a better understanding of an application startup process.

You can choose an ApplicationStartup implementation when setting up the SpringApplication instance. For example, to use the BufferingApplicationStartup, you could write:

Java
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.metrics.buffering.BufferingApplicationStartup;

@SpringBootApplication
public class MyApplication {

    public static void main(String[] args) {
        SpringApplication application = new SpringApplication(MyApplication.class);
        application.setApplicationStartup(new BufferingApplicationStartup(2048));
        application.run(args);
    }

}
Kotlin
import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.context.metrics.buffering.BufferingApplicationStartup
import org.springframework.boot.runApplication

@SpringBootApplication
class MyApplication

fun main(args: Array<String>) {
    runApplication<MyApplication>(*args) {
        applicationStartup = BufferingApplicationStartup(2048)
    }
}

The first available implementation, FlightRecorderApplicationStartup is provided by Spring Framework. It adds Spring-specific startup events to a Java Flight Recorder session and is meant for profiling applications and correlating their Spring context lifecycle with JVM events (such as allocations, GCs, class loading…​). Once configured, you can record data by running the application with the Flight Recorder enabled:

$ java -XX:StartFlightRecording:filename=recording.jfr,duration=10s -jar demo.jar

Spring Boot ships with the BufferingApplicationStartup variant; this implementation is meant for buffering the startup steps and draining them into an external metrics system. Applications can ask for the bean of type BufferingApplicationStartup in any component.

Spring Boot can also be configured to expose a startup endpoint that provides this information as a JSON document.

7.2. Externalized Configuration

Spring Boot lets you externalize your configuration so that you can work with the same application code in different environments. You can use a variety of external configuration sources including Java properties files, YAML files, environment variables, and command-line arguments.

Property values can be injected directly into your beans by using the @Value annotation, accessed through Spring’s Environment abstraction, or be bound to structured objects through @ConfigurationProperties.

Spring Boot uses a very particular PropertySource order that is designed to allow sensible overriding of values. Later property sources can override the values defined in earlier ones. Sources are considered in the following order:

  1. Default properties (specified by setting SpringApplication.setDefaultProperties).

  2. @PropertySource annotations on your @Configuration classes. Please note that such property sources are not added to the Environment until the application context is being refreshed. This is too late to configure certain properties such as logging.* and spring.main.* which are read before refresh begins.

  3. Config data (such as application.properties files).

  4. A RandomValuePropertySource that has properties only in random.*.

  5. OS environment variables.

  6. Java System properties (System.getProperties()).

  7. JNDI attributes from java:comp/env.

  8. ServletContext init parameters.

  9. ServletConfig init parameters.

  10. Properties from SPRING_APPLICATION_JSON (inline JSON embedded in an environment variable or system property).

  11. Command line arguments.

  12. properties attribute on your tests. Available on @SpringBootTest and the test annotations for testing a particular slice of your application.

  13. @DynamicPropertySource annotations in your tests.

  14. @TestPropertySource annotations on your tests.

  15. Devtools global settings properties in the $HOME/.config/spring-boot directory when devtools is active.

Config data files are considered in the following order:

  1. Application properties packaged inside your jar (application.properties and YAML variants).

  2. Profile-specific application properties packaged inside your jar (application-{profile}.properties and YAML variants).

  3. Application properties outside of your packaged jar (application.properties and YAML variants).

  4. Profile-specific application properties outside of your packaged jar (application-{profile}.properties and YAML variants).

It is recommended to stick with one format for your entire application. If you have configuration files with both .properties and YAML format in the same location, .properties takes precedence.
If you use environment variables rather than system properties, most operating systems disallow period-separated key names, but you can use underscores instead (for example, SPRING_CONFIG_NAME instead of spring.config.name). See Binding From Environment Variables for details.
If your application runs in a servlet container or application server, then JNDI properties (in java:comp/env) or servlet context initialization parameters can be used instead of, or as well as, environment variables or system properties.

To provide a concrete example, suppose you develop a @Component that uses a name property, as shown in the following example:

Java
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

    @Value("${name}")
    private String name;

    // ...

}
Kotlin
import org.springframework.beans.factory.annotation.Value
import org.springframework.stereotype.Component

@Component
class MyBean {

    @Value("\${name}")
    private val name: String? = null

    // ...

}

On your application classpath (for example, inside your jar) you can have an application.properties file that provides a sensible default property value for name. When running in a new environment, an application.properties file can be provided outside of your jar that overrides the name. For one-off testing, you can launch with a specific command line switch (for example, java -jar app.jar --name="Spring").

The env and configprops endpoints can be useful in determining why a property has a particular value. You can use these two endpoints to diagnose unexpected property values. See the "Production ready features" section for details.

7.2.1. Accessing Command Line Properties

By default, SpringApplication converts any command line option arguments (that is, arguments starting with --, such as --server.port=9000) to a property and adds them to the Spring Environment. As mentioned previously, command line properties always take precedence over file-based property sources.

If you do not want command line properties to be added to the Environment, you can disable them by using SpringApplication.setAddCommandLineProperties(false).

7.2.2. JSON Application Properties

Environment variables and system properties often have restrictions that mean some property names cannot be used. To help with this, Spring Boot allows you to encode a block of properties into a single JSON structure.

When your application starts, any spring.application.json or SPRING_APPLICATION_JSON properties will be parsed and added to the Environment.

For example, the SPRING_APPLICATION_JSON property can be supplied on the command line in a UN*X shell as an environment variable:

$ SPRING_APPLICATION_JSON='{"my":{"name":"test"}}' java -jar myapp.jar

In the preceding example, you end up with my.name=test in the Spring Environment.

The same JSON can also be provided as a system property:

$ java -Dspring.application.json='{"my":{"name":"test"}}' -jar myapp.jar

Or you could supply the JSON by using a command line argument:

$ java -jar myapp.jar --spring.application.json='{"my":{"name":"test"}}'

If you are deploying to a classic Application Server, you could also use a JNDI variable named java:comp/env/spring.application.json.

Although null values from the JSON will be added to the resulting property source, the PropertySourcesPropertyResolver treats null properties as missing values. This means that the JSON cannot override properties from lower order property sources with a null value.

7.2.3. External Application Properties

Spring Boot will automatically find and load application.properties and application.yaml files from the following locations when your application starts:

  1. From the classpath

    1. The classpath root

    2. The classpath /config package

  2. From the current directory

    1. The current directory

    2. The config/ subdirectory in the current directory

    3. Immediate child directories of the config/ subdirectory

The list is ordered by precedence (with values from lower items overriding earlier ones). Documents from the loaded files are added as PropertySources to the Spring Environment.

If you do not like application as the configuration file name, you can switch to another file name by specifying a spring.config.name environment property. For example, to look for myproject.properties and myproject.yaml files you can run your application as follows:

$ java -jar myproject.jar --spring.config.name=myproject

You can also refer to an explicit location by using the spring.config.location environment property. This property accepts a comma-separated list of one or more locations to check.

The following example shows how to specify two distinct files:

$ java -jar myproject.jar --spring.config.location=\
    optional:classpath:/default.properties,\
    optional:classpath:/override.properties
Use the prefix optional: if the locations are optional and you do not mind if they do not exist.
spring.config.name, spring.config.location, and spring.config.additional-location are used very early to determine which files have to be loaded. They must be defined as an environment property (typically an OS environment variable, a system property, or a command-line argument).

If spring.config.location contains directories (as opposed to files), they should end in /. At runtime they will be appended with the names generated from spring.config.name before being loaded. Files specified in spring.config.location are imported directly.

Both directory and file location values are also expanded to check for profile-specific files. For example, if you have a spring.config.location of classpath:myconfig.properties, you will also find appropriate classpath:myconfig-<profile>.properties files are loaded.

In most situations, each spring.config.location item you add will reference a single file or directory. Locations are processed in the order that they are defined and later ones can override the values of earlier ones.

If you have a complex location setup, and you use profile-specific configuration files, you may need to provide further hints so that Spring Boot knows how they should be grouped. A location group is a collection of locations that are all considered at the same level. For example, you might want to group all classpath locations, then all external locations. Items within a location group should be separated with ;. See the example in the “Profile Specific Files” section for more details.

Locations configured by using spring.config.location replace the default locations. For example, if spring.config.location is configured with the value optional:classpath:/custom-config/,optional:file:./custom-config/, the complete set of locations considered is:

  1. optional:classpath:custom-config/

  2. optional:file:./custom-config/

If you prefer to add additional locations, rather than replacing them, you can use spring.config.additional-location. Properties loaded from additional locations can override those in the default locations. For example, if spring.config.additional-location is configured with the value optional:classpath:/custom-config/,optional:file:./custom-config/, the complete set of locations considered is:

  1. optional:classpath:/;optional:classpath:/config/

  2. optional:file:./;optional:file:./config/;optional:file:./config/*/

  3. optional:classpath:custom-config/

  4. optional:file:./custom-config/

This search ordering lets you specify default values in one configuration file and then selectively override those values in another. You can provide default values for your application in application.properties (or whatever other basename you choose with spring.config.name) in one of the default locations. These default values can then be overridden at runtime with a different file located in one of the custom locations.

Optional Locations

By default, when a specified config data location does not exist, Spring Boot will throw a ConfigDataLocationNotFoundException and your application will not start.

If you want to specify a location, but you do not mind if it does not always exist, you can use the optional: prefix. You can use this prefix with the spring.config.location and spring.config.additional-location properties, as well as with spring.config.import declarations.

For example, a spring.config.import value of optional:file:./myconfig.properties allows your application to start, even if the myconfig.properties file is missing.

If you want to ignore all ConfigDataLocationNotFoundExceptions and always continue to start your application, you can use the spring.config.on-not-found property. Set the value to ignore using SpringApplication.setDefaultProperties(…​) or with a system/environment variable.

Wildcard Locations

If a config file location includes the * character for the last path segment, it is considered a wildcard location. Wildcards are expanded when the config is loaded so that immediate subdirectories are also checked. Wildcard locations are particularly useful in an environment such as Kubernetes when there are multiple sources of config properties.

For example, if you have some Redis configuration and some MySQL configuration, you might want to keep those two pieces of configuration separate, while requiring that both those are present in an application.properties file. This might result in two separate application.properties files mounted at different locations such as /config/redis/application.properties and /config/mysql/application.properties. In such a case, having a wildcard location of config/*/, will result in both files being processed.

By default, Spring Boot includes config/*/ in the default search locations. It means that all subdirectories of the /config directory outside of your jar will be searched.

You can use wildcard locations yourself with the spring.config.location and spring.config.additional-location properties.

A wildcard location must contain only one * and end with */ for search locations that are directories or */<filename> for search locations that are files. Locations with wildcards are sorted alphabetically based on the absolute path of the file names.
Wildcard locations only work with external directories. You cannot use a wildcard in a classpath: location.
Profile Specific Files

As well as application property files, Spring Boot will also attempt to load profile-specific files using the naming convention application-{profile}. For example, if your application activates a profile named prod and uses YAML files, then both application.yaml and application-prod.yaml will be considered.

Profile-specific properties are loaded from the same locations as standard application.properties, with profile-specific files always overriding the non-specific ones. If several profiles are specified, a last-wins strategy applies. For example, if profiles prod,live are specified by the spring.profiles.active property, values in application-prod.properties can be overridden by those in application-live.properties.

The last-wins strategy applies at the location group level. A spring.config.location of classpath:/cfg/,classpath:/ext/ will not have the same override rules as classpath:/cfg/;classpath:/ext/.

For example, continuing our prod,live example above, we might have the following files:

/cfg
  application-live.properties
/ext
  application-live.properties
  application-prod.properties

When we have a spring.config.location of classpath:/cfg/,classpath:/ext/ we process all /cfg files before all /ext files:

  1. /cfg/application-live.properties

  2. /ext/application-prod.properties

  3. /ext/application-live.properties

When we have classpath:/cfg/;classpath:/ext/ instead (with a ; delimiter) we process /cfg and /ext at the same level:

  1. /ext/application-prod.properties

  2. /cfg/application-live.properties

  3. /ext/application-live.properties

The Environment has a set of default profiles (by default, [default]) that are used if no active profiles are set. In other words, if no profiles are explicitly activated, then properties from application-default are considered.

Properties files are only ever loaded once. If you have already directly imported a profile specific property files then it will not be imported a second time.
Importing Additional Data

Application properties may import further config data from other locations using the spring.config.import property. Imports are processed as they are discovered, and are treated as additional documents inserted immediately below the one that declares the import.

For example, you might have the following in your classpath application.properties file:

Properties
spring.application.name=myapp
spring.config.import=optional:file:./dev.properties
Yaml
spring:
  application:
    name: "myapp"
  config:
    import: "optional:file:./dev.properties"

This will trigger the import of a dev.properties file in current directory (if such a file exists). Values from the imported dev.properties will take precedence over the file that triggered the import. In the above example, the dev.properties could redefine spring.application.name to a different value.

An import will only be imported once no matter how many times it is declared. The order an import is defined inside a single document within the properties/yaml file does not matter. For instance, the two examples below produce the same result:

Properties
spring.config.import=my.properties
my.property=value
Yaml
spring:
  config:
    import: "my.properties"
my:
  property: "value"
Properties
my.property=value
spring.config.import=my.properties
Yaml
my:
  property: "value"
spring:
  config:
    import: "my.properties"

In both of the above examples, the values from the my.properties file will take precedence over the file that triggered its import.

Several locations can be specified under a single spring.config.import key. Locations will be processed in the order that they are defined, with later imports taking precedence.

When appropriate, Profile-specific variants are also considered for import. The example above would import both my.properties as well as any my-<profile>.properties variants.

Spring Boot includes pluggable API that allows various different location addresses to be supported. By default you can import Java Properties, YAML and “configuration trees”.

Third-party jars can offer support for additional technologies (there is no requirement for files to be local). For example, you can imagine config data being from external stores such as Consul, Apache ZooKeeper or Netflix Archaius.

If you want to support your own locations, see the ConfigDataLocationResolver and ConfigDataLoader classes in the org.springframework.boot.context.config package.

Importing Extensionless Files

Some cloud platforms cannot add a file extension to volume mounted files. To import these extensionless files, you need to give Spring Boot a hint so that it knows how to load them. You can do this by putting an extension hint in square brackets.

For example, suppose you have a /etc/config/myconfig file that you wish to import as yaml. You can import it from your application.properties using the following:

Properties
spring.config.import=file:/etc/config/myconfig[.yaml]
Yaml
spring:
  config:
    import: "file:/etc/config/myconfig[.yaml]"
Using Configuration Trees

When running applications on a cloud platform (such as Kubernetes) you often need to read config values that the platform supplies. It is not uncommon to use environment variables for such purposes, but this can have drawbacks, especially if the value is supposed to be kept secret.

As an alternative to environment variables, many cloud platforms now allow you to map configuration into mounted data volumes. For example, Kubernetes can volume mount both ConfigMaps and Secrets.

There are two common volume mount patterns that can be used:

  1. A single file contains a complete set of properties (usually written as YAML).

  2. Multiple files are written to a directory tree, with the filename becoming the ‘key’ and the contents becoming the ‘value’.

For the first case, you can import the YAML or Properties file directly using spring.config.import as described above. For the second case, you need to use the configtree: prefix so that Spring Boot knows it needs to expose all the files as properties.

As an example, let’s imagine that Kubernetes has mounted the following volume:

etc/
  config/
    myapp/
      username
      password

The contents of the username file would be a config value, and the contents of password would be a secret.

To import these properties, you can add the following to your application.properties or application.yaml file:

Properties
spring.config.import=optional:configtree:/etc/config/
Yaml
spring:
  config:
    import: "optional:configtree:/etc/config/"

You can then access or inject myapp.username and myapp.password properties from the Environment in the usual way.

The names of the folders and files under the config tree form the property name. In the above example, to access the properties as username and password, you can set spring.config.import to optional:configtree:/etc/config/myapp.
Filenames with dot notation are also correctly mapped. For example, in the above example, a file named myapp.username in /etc/config would result in a myapp.username property in the Environment.
Configuration tree values can be bound to both string String and byte[] types depending on the contents expected.

If you have multiple config trees to import from the same parent folder you can use a wildcard shortcut. Any configtree: location that ends with /*/ will import all immediate children as config trees. As with a non-wildcard import, the names of the folders and files under each config tree form the property name.

For example, given the following volume:

etc/
  config/
    dbconfig/
      db/
        username
        password
    mqconfig/
      mq/
        username
        password

You can use configtree:/etc/config/*/ as the import location:

Properties
spring.config.import=optional:configtree:/etc/config/*/
Yaml
spring:
  config:
    import: "optional:configtree:/etc/config/*/"

This will add db.username, db.password, mq.username and mq.password properties.

Directories loaded using a wildcard are sorted alphabetically. If you need a different order, then you should list each location as a separate import

Configuration trees can also be used for Docker secrets. When a Docker swarm service is granted access to a secret, the secret gets mounted into the container. For example, if a secret named db.password is mounted at location /run/secrets/, you can make db.password available to the Spring environment using the following:

Properties
spring.config.import=optional:configtree:/run/secrets/
Yaml
spring:
  config:
    import: "optional:configtree:/run/secrets/"
Property Placeholders

The values in application.properties and application.yaml are filtered through the existing Environment when they are used, so you can refer back to previously defined values (for example, from System properties or environment variables). The standard ${name} property-placeholder syntax can be used anywhere within a value. Property placeholders can also specify a default value using a : to separate the default value from the property name, for example ${name:default}.

The use of placeholders with and without defaults is shown in the following example:

Properties
app.name=MyApp
app.description=${app.name} is a Spring Boot application written by ${username:Unknown}
Yaml
app:
  name: "MyApp"
  description: "${app.name} is a Spring Boot application written by ${username:Unknown}"

Assuming that the username property has not been set elsewhere, app.description will have the value MyApp is a Spring Boot application written by Unknown.

You should always refer to property names in the placeholder using their canonical form (kebab-case using only lowercase letters). This will allow Spring Boot to use the same logic as it does when relaxed binding @ConfigurationProperties.

For example, ${demo.item-price} will pick up demo.item-price and demo.itemPrice forms from the application.properties file, as well as DEMO_ITEMPRICE from the system environment. If you used ${demo.itemPrice} instead, demo.item-price and DEMO_ITEMPRICE would not be considered.

You can also use this technique to create “short” variants of existing Spring Boot properties. See the Use ‘Short’ Command Line Arguments how-to for details.
Working With Multi-Document Files

Spring Boot allows you to split a single physical file into multiple logical documents which are each added independently. Documents are processed in order, from top to bottom. Later documents can override the properties defined in earlier ones.

For application.yaml files, the standard YAML multi-document syntax is used. Three consecutive hyphens represent the end of one document, and the start of the next.

For example, the following file has two logical documents:

spring:
  application:
    name: "MyApp"
---
spring:
  application:
    name: "MyCloudApp"
  config:
    activate:
      on-cloud-platform: "kubernetes"

For application.properties files a special #--- or !--- comment is used to mark the document splits:

spring.application.name=MyApp
#---
spring.application.name=MyCloudApp
spring.config.activate.on-cloud-platform=kubernetes
Property file separators must not have any leading whitespace and must have exactly three hyphen characters. The lines immediately before and after the separator must not be same comment prefix.
Multi-document property files are often used in conjunction with activation properties such as spring.config.activate.on-profile. See the next section for details.
Multi-document property files cannot be loaded by using the @PropertySource or @TestPropertySource annotations.
Activation Properties

It is sometimes useful to only activate a given set of properties when certain conditions are met. For example, you might have properties that are only relevant when a specific profile is active.

You can conditionally activate a properties document using spring.config.activate.*.

The following activation properties are available:

Table 5. activation properties
Property Note

on-profile

A profile expression that must match for the document to be active.

on-cloud-platform

The CloudPlatform that must be detected for the document to be active.

For example, the following specifies that the second document is only active when running on Kubernetes, and only when either the “prod” or “staging” profiles are active:

Properties
myprop=always-set
#---
spring.config.activate.on-cloud-platform=kubernetes
spring.config.activate.on-profile=prod | staging
myotherprop=sometimes-set
Yaml
myprop:
  "always-set"
---
spring:
  config:
    activate:
      on-cloud-platform: "kubernetes"
      on-profile: "prod | staging"
myotherprop: "sometimes-set"

7.2.4. Encrypting Properties

Spring Boot does not provide any built-in support for encrypting property values, however, it does provide the hook points necessary to modify values contained in the Spring Environment. The EnvironmentPostProcessor interface allows you to manipulate the Environment before the application starts. See Customize the Environment or ApplicationContext Before It Starts for details.

If you need a secure way to store credentials and passwords, the Spring Cloud Vault project provides support for storing externalized configuration in HashiCorp Vault.

7.2.5. Working With YAML

YAML is a superset of JSON and, as such, is a convenient format for specifying hierarchical configuration data. The SpringApplication class automatically supports YAML as an alternative to properties whenever you have the SnakeYAML library on your classpath.

If you use “Starters”, SnakeYAML is automatically provided by spring-boot-starter.
Mapping YAML to Properties

YAML documents need to be converted from their hierarchical format to a flat structure that can be used with the Spring Environment. For example, consider the following YAML document:

environments:
  dev:
    url: "https://dev.example.com"
    name: "Developer Setup"
  prod:
    url: "https://another.example.com"
    name: "My Cool App"

In order to access these properties from the Environment, they would be flattened as follows:

environments.dev.url=https://dev.example.com
environments.dev.name=Developer Setup
environments.prod.url=https://another.example.com
environments.prod.name=My Cool App

Likewise, YAML lists also need to be flattened. They are represented as property keys with [index] dereferencers. For example, consider the following YAML:

my:
 servers:
 - "dev.example.com"
 - "another.example.com"

The preceding example would be transformed into these properties:

my.servers[0]=dev.example.com
my.servers[1]=another.example.com
Properties that use the [index] notation can be bound to Java List or Set objects using Spring Boot’s Binder class. For more details see the “Type-safe Configuration Properties” section below.
YAML files cannot be loaded by using the @PropertySource or @TestPropertySource annotations. So, in the case that you need to load values that way, you need to use a properties file.
Directly Loading YAML

Spring Framework provides two convenient classes that can be used to load YAML documents. The YamlPropertiesFactoryBean loads YAML as Properties and the YamlMapFactoryBean loads YAML as a Map.

You can also use the YamlPropertySourceLoader class if you want to load YAML as a Spring PropertySource.

7.2.6. Configuring Random Values

The RandomValuePropertySource is useful for injecting random values (for example, into secrets or test cases). It can produce integers, longs, uuids, or strings, as shown in the following example:

Properties
my.secret=${random.value}
my.number=${random.int}
my.bignumber=${random.long}
my.uuid=${random.uuid}
my.number-less-than-ten=${random.int(10)}
my.number-in-range=${random.int[1024,65536]}
Yaml
my:
  secret: "${random.value}"
  number: "${random.int}"
  bignumber: "${random.long}"
  uuid: "${random.uuid}"
  number-less-than-ten: "${random.int(10)}"
  number-in-range: "${random.int[1024,65536]}"

The random.int* syntax is OPEN value (,max) CLOSE where the OPEN,CLOSE are any character and value,max are integers. If max is provided, then value is the minimum value and max is the maximum value (exclusive).

7.2.7. Configuring System Environment Properties

Spring Boot supports setting a prefix for environment properties. This is useful if the system environment is shared by multiple Spring Boot applications with different configuration requirements. The prefix for system environment properties can be set directly on SpringApplication.

For example, if you set the prefix to input, a property such as remote.timeout will also be resolved as input.remote.timeout in the system environment.

7.2.8. Type-safe Configuration Properties

Using the @Value("${property}") annotation to inject configuration properties can sometimes be cumbersome, especially if you are working with multiple properties or your data is hierarchical in nature. Spring Boot provides an alternative method of working with properties that lets strongly typed beans govern and validate the configuration of your application.

JavaBean Properties Binding

It is possible to bind a bean declaring standard JavaBean properties as shown in the following example:

Java
import java.net.InetAddress;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties("my.service")
public class MyProperties {

    private boolean enabled;

    private InetAddress remoteAddress;

    private final Security security = new Security();

    // getters / setters...

    public boolean isEnabled() {
        return this.enabled;
    }

    public void setEnabled(boolean enabled) {
        this.enabled = enabled;
    }

    public InetAddress getRemoteAddress() {
        return this.remoteAddress;
    }

    public void setRemoteAddress(InetAddress remoteAddress) {
        this.remoteAddress = remoteAddress;
    }

    public Security getSecurity() {
        return this.security;
    }

    public static class Security {

        private String username;

        private String password;

        private List<String> roles = new ArrayList<>(Collections.singleton("USER"));

        // getters / setters...

        public String getUsername() {
            return this.username;
        }

        public void setUsername(String username) {
            this.username = username;
        }

        public String getPassword() {
            return this.password;
        }

        public void setPassword(String password) {
            this.password = password;
        }

        public List<String> getRoles() {
            return this.roles;
        }

        public void setRoles(List<String> roles) {
            this.roles = roles;
        }

    }

}
Kotlin
import org.springframework.boot.context.properties.ConfigurationProperties
import java.net.InetAddress

@ConfigurationProperties("my.service")
class MyProperties {

    var isEnabled = false

    var remoteAddress: InetAddress? = null

    val security = Security()

    class Security {

        var username: String? = null

        var password: String? = null

        var roles: List<String> = ArrayList(setOf("USER"))

    }

}

The preceding POJO defines the following properties:

  • my.service.enabled, with a value of false by default.

  • my.service.remote-address, with a type that can be coerced from String.

  • my.service.security.username, with a nested "security" object whose name is determined by the name of the property. In particular, the type is not used at all there and could have been SecurityProperties.

  • my.service.security.password.

  • my.service.security.roles, with a collection of String that defaults to USER.

The properties that map to @ConfigurationProperties classes available in Spring Boot, which are configured through properties files, YAML files, environment variables, and other mechanisms, are public API but the accessors (getters/setters) of the class itself are not meant to be used directly.

Such arrangement relies on a default empty constructor and getters and setters are usually mandatory, since binding is through standard Java Beans property descriptors, just like in Spring MVC. A setter may be omitted in the following cases:

  • Maps, as long as they are initialized, need a getter but not necessarily a setter, since they can be mutated by the binder.

  • Collections and arrays can be accessed either through an index (typically with YAML) or by using a single comma-separated value (properties). In the latter case, a setter is mandatory. We recommend to always add a setter for such types. If you initialize a collection, make sure it is not immutable (as in the preceding example).

  • If nested POJO properties are initialized (like the Security field in the preceding example), a setter is not required. If you want the binder to create the instance on the fly by using its default constructor, you need a setter.

Some people use Project Lombok to add getters and setters automatically. Make sure that Lombok does not generate any particular constructor for such a type, as it is used automatically by the container to instantiate the object.

Finally, only standard Java Bean properties are considered and binding on static properties is not supported.

Constructor Binding

The example in the previous section can be rewritten in an immutable fashion as shown in the following example:

Java
import java.net.InetAddress;
import java.util.List;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.context.properties.ConstructorBinding;
import org.springframework.boot.context.properties.bind.DefaultValue;

@ConstructorBinding
@ConfigurationProperties("my.service")
public class MyProperties {

    // fields...

    private final boolean enabled;

    private final InetAddress remoteAddress;

    private final Security security;

    public MyProperties(boolean enabled, InetAddress remoteAddress, Security security) {
        this.enabled = enabled;
        this.remoteAddress = remoteAddress;
        this.security = security;
    }

    // getters...

    public boolean isEnabled() {
        return this.enabled;
    }

    public InetAddress getRemoteAddress() {
        return this.remoteAddress;
    }

    public Security getSecurity() {
        return this.security;
    }

    public static class Security {

        // fields...

        private final String username;

        private final String password;

        private final List<String> roles;

        public Security(String username, String password, @DefaultValue("USER") List<String> roles) {
            this.username = username;
            this.password = password;
            this.roles = roles;
        }

        // getters...

        public String getUsername() {
            return this.username;
        }

        public String getPassword() {
            return this.password;
        }

        public List<String> getRoles() {
            return this.roles;
        }

    }

}
Kotlin
import org.springframework.boot.context.properties.ConfigurationProperties
import org.springframework.boot.context.properties.ConstructorBinding
import org.springframework.boot.context.properties.bind.DefaultValue
import java.net.InetAddress

@ConstructorBinding
@ConfigurationProperties("my.service")
class MyProperties(val enabled: Boolean, val remoteAddress: InetAddress,
        val security: Security) {

    class Security(val username: String, val password: String,
            @param:DefaultValue("USER") val roles: List<String>)

}

In this setup, the @ConstructorBinding annotation is used to indicate that constructor binding should be used. This means that the binder will expect to find a constructor with the parameters that you wish to have bound. If you are using Java 16 or later, constructor binding can be used with records. In this case, unless your record has multiple constructors, there is no need to use @ConstructorBinding.

Nested members of a @ConstructorBinding class (such as Security in the example above) will also be bound through their constructor.

Default values can be specified using @DefaultValue on a constructor parameter or, when using Java 16 or later, a record component. The conversion service will be applied to coerce the String value to the target type of a missing property.

Referring to the previous example, if no properties are bound to Security, the MyProperties instance will contain a null value for security. To make it contain a non-null instance of Security even when no properties are bound to it (when using Kotlin, this will require the username and password parameters of Security to be declared as nullable as they do not have default values), use an empty @DefaultValue annotation:

Java
public MyProperties(boolean enabled, InetAddress remoteAddress, @DefaultValue Security security) {
    this.enabled = enabled;
    this.remoteAddress = remoteAddress;
    this.security = security;
}
Kotlin
class MyProperties(val enabled: Boolean, val remoteAddress: InetAddress,
        @DefaultValue val security: Security) {

    class Security(val username: String?, val password: String?,
            @param:DefaultValue("USER") val roles: List<String>)

}
To use constructor binding the class must be enabled using @EnableConfigurationProperties or configuration property scanning. You cannot use constructor binding with beans that are created by the regular Spring mechanisms (for example @Component beans, beans created by using @Bean methods or beans loaded by using @Import)
If you have more than one constructor for your class you can also use @ConstructorBinding directly on the constructor that should be bound.
The use of java.util.Optional with @ConfigurationProperties is not recommended as it is primarily intended for use as a return type. As such, it is not well-suited to configuration property injection. For consistency with properties of other types, if you do declare an Optional property and it has no value, null rather than an empty Optional will be bound.
Enabling @ConfigurationProperties-annotated Types

Spring Boot provides infrastructure to bind @ConfigurationProperties types and register them as beans. You can either enable configuration properties on a class-by-class basis or enable configuration property scanning that works in a similar manner to component scanning.

Sometimes, classes annotated with @ConfigurationProperties might not be suitable for scanning, for example, if you’re developing your own auto-configuration or you want to enable them conditionally. In these cases, specify the list of types to process using the @EnableConfigurationProperties annotation. This can be done on any @Configuration class, as shown in the following example:

Java
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Configuration;

@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(SomeProperties.class)
public class MyConfiguration {

}
Kotlin
import org.springframework.boot.context.properties.EnableConfigurationProperties
import org.springframework.context.annotation.Configuration

@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(SomeProperties::class)
class MyConfiguration
Java
import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties("some.properties")
public class SomeProperties {

}
Kotlin
import org.springframework.boot.context.properties.ConfigurationProperties

@ConfigurationProperties("some.properties")
class SomeProperties

To use configuration property scanning, add the @ConfigurationPropertiesScan annotation to your application. Typically, it is added to the main application class that is annotated with @SpringBootApplication but it can be added to any @Configuration class. By default, scanning will occur from the package of the class that declares the annotation. If you want to define specific packages to scan, you can do so as shown in the following example:

Java
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.properties.ConfigurationPropertiesScan;

@SpringBootApplication
@ConfigurationPropertiesScan({ "com.example.app", "com.example.another" })
public class MyApplication {

}
Kotlin
import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.context.properties.ConfigurationPropertiesScan

@SpringBootApplication
@ConfigurationPropertiesScan("com.example.app", "com.example.another")
class MyApplication

When the @ConfigurationProperties bean is registered using configuration property scanning or through @EnableConfigurationProperties, the bean has a conventional name: <prefix>-<fqn>, where <prefix> is the environment key prefix specified in the @ConfigurationProperties annotation and <fqn> is the fully qualified name of the bean. If the annotation does not provide any prefix, only the fully qualified name of the bean is used.

Assuming that it is in the com.example.app package, the bean name of the SomeProperties example above is some.properties-com.example.app.SomeProperties.

We recommend that @ConfigurationProperties only deal with the environment and, in particular, does not inject other beans from the context. For corner cases, setter injection can be used or any of the *Aware interfaces provided by the framework (such as EnvironmentAware if you need access to the Environment). If you still want to inject other beans using the constructor, the configuration properties bean must be annotated with @Component and use JavaBean-based property binding.

Using @ConfigurationProperties-annotated Types

This style of configuration works particularly well with the SpringApplication external YAML configuration, as shown in the following example:

my:
  service:
    remote-address: 192.168.1.1
    security:
      username: "admin"
      roles:
      - "USER"
      - "ADMIN"

To work with @ConfigurationProperties beans, you can inject them in the same way as any other bean, as shown in the following example:

Java
import org.springframework.stereotype.Service;

@Service
public class MyService {

    private final MyProperties properties;

    public MyService(MyProperties properties) {
        this.properties = properties;
    }

    public void openConnection() {
        Server server = new Server(this.properties.getRemoteAddress());
        server.start();
        // ...
    }

    // ...

}
Kotlin
import org.springframework.stereotype.Service

@Service
class MyService(val properties: MyProperties) {

    fun openConnection() {
        val server = Server(properties.remoteAddress)
        server.start()
        // ...
    }

    // ...

}
Using @ConfigurationProperties also lets you generate metadata files that can be used by IDEs to offer auto-completion for your own keys. See the appendix for details.
Third-party Configuration

As well as using @ConfigurationProperties to annotate a class, you can also use it on public @Bean methods. Doing so can be particularly useful when you want to bind properties to third-party components that are outside of your control.

To configure a bean from the Environment properties, add @ConfigurationProperties to its bean registration, as shown in the following example:

Java
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration(proxyBeanMethods = false)
public class ThirdPartyConfiguration {

    @Bean
    @ConfigurationProperties(prefix = "another")
    public AnotherComponent anotherComponent() {
        return new AnotherComponent();
    }

}
Kotlin
import org.springframework.boot.context.properties.ConfigurationProperties
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration

@Configuration(proxyBeanMethods = false)
class ThirdPartyConfiguration {

    @Bean
    @ConfigurationProperties(prefix = "another")
    fun anotherComponent(): AnotherComponent = AnotherComponent()

}

Any JavaBean property defined with the another prefix is mapped onto that AnotherComponent bean in manner similar to the preceding SomeProperties example.

Relaxed Binding

Spring Boot uses some relaxed rules for binding Environment properties to @ConfigurationProperties beans, so there does not need to be an exact match between the Environment property name and the bean property name. Common examples where this is useful include dash-separated environment properties (for example, context-path binds to contextPath), and capitalized environment properties (for example, PORT binds to port).

As an example, consider the following @ConfigurationProperties class:

Java
import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties(prefix = "my.main-project.person")
public class MyPersonProperties {

    private String firstName;

    public String getFirstName() {
        return this.firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

}
Kotlin
import org.springframework.boot.context.properties.ConfigurationProperties

@ConfigurationProperties(prefix = "my.main-project.person")
class MyPersonProperties {

    var firstName: String? = null

}

With the preceding code, the following properties names can all be used:

Table 6. relaxed binding
Property Note

my.main-project.person.first-name

Kebab case, which is recommended for use in .properties and YAML files.

my.main-project.person.firstName

Standard camel case syntax.

my.main-project.person.first_name

Underscore notation, which is an alternative format for use in .properties and YAML files.

MY_MAINPROJECT_PERSON_FIRSTNAME

Upper case format, which is recommended when using system environment variables.

The prefix value for the annotation must be in kebab case (lowercase and separated by -, such as my.main-project.person).
Table 7. relaxed binding rules per property source
Property Source Simple List

Properties Files

Camel case, kebab case, or underscore notation

Standard list syntax using [ ] or comma-separated values

YAML Files

Camel case, kebab case, or underscore notation

Standard YAML list syntax or comma-separated values

Environment Variables

Upper case format with underscore as the delimiter (see Binding From Environment Variables).

Numeric values surrounded by underscores (see Binding From Environment Variables)

System properties

Camel case, kebab case, or underscore notation

Standard list syntax using [ ] or comma-separated values

We recommend that, when possible, properties are stored in lower-case kebab format, such as my.person.first-name=Rod.
Binding Maps

When binding to Map properties you may need to use a special bracket notation so that the original key value is preserved. If the key is not surrounded by [], any characters that are not alpha-numeric, - or . are removed.

For example, consider binding the following properties to a Map<String,String>:

Properties
my.map.[/key1]=value1
my.map.[/key2]=value2
my.map./key3=value3
Yaml
my:
  map:
    "[/key1]": "value1"
    "[/key2]": "value2"
    "/key3": "value3"
For YAML files, the brackets need to be surrounded by quotes for the keys to be parsed properly.

The properties above will bind to a Map with /key1, /key2 and key3 as the keys in the map. The slash has been removed from key3 because it was not surrounded by square brackets.

When binding to scalar values, keys with . in them do not need to be surrounded by []. Scalar values include enums and all types in the java.lang package except for Object. Binding a.b=c to Map<String, String> will preserve the . in the key and return a Map with the entry {"a.b"="c"}. For any other types you need to use the bracket notation if your key contains a .. For example, binding a.b=c to Map<String, Object> will return a Map with the entry {"a"={"b"="c"}} whereas [a.b]=c will return a Map with the entry {"a.b"="c"}.

Binding From Environment Variables

Most operating systems impose strict rules around the names that can be used for environment variables. For example, Linux shell variables can contain only letters (a to z or A to Z), numbers (0 to 9) or the underscore character (_). By convention, Unix shell variables will also have their names in UPPERCASE.

Spring Boot’s relaxed binding rules are, as much as possible, designed to be compatible with these naming restrictions.

To convert a property name in the canonical-form to an environment variable name you can follow these rules:

  • Replace dots (.) with underscores (_).

  • Remove any dashes (-).

  • Convert to uppercase.

For example, the configuration property spring.main.log-startup-info would be an environment variable named SPRING_MAIN_LOGSTARTUPINFO.

Environment variables can also be used when binding to object lists. To bind to a List, the element number should be surrounded with underscores in the variable name.

For example, the configuration property my.service[0].other would use an environment variable named MY_SERVICE_0_OTHER.

Caching

Relaxed binding uses a cache to improve performance. By default, this caching is only applied to immutable property sources. To customize this behavior, for example to enable caching for mutable property sources, use ConfigurationPropertyCaching.

Merging Complex Types

When lists are configured in more than one place, overriding works by replacing the entire list.

For example, assume a MyPojo object with name and description attributes that are null by default. The following example exposes a list of MyPojo objects from MyProperties:

Java
import java.util.ArrayList;
import java.util.List;

import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties("my")
public class MyProperties {

    private final List<MyPojo> list = new ArrayList<>();

    public List<MyPojo> getList() {
        return this.list;
    }

}
Kotlin
import org.springframework.boot.context.properties.ConfigurationProperties

@ConfigurationProperties("my")
class MyProperties {

    val list: List<MyPojo> = ArrayList()

}

Consider the following configuration:

Properties
my.list[0].name=my name
my.list[0].description=my description
#---
spring.config.activate.on-profile=dev
my.list[0].name=my another name
Yaml
my:
  list:
  - name: "my name"
    description: "my description"
---
spring:
  config:
    activate:
      on-profile: "dev"
my:
  list:
  - name: "my another name"

If the dev profile is not active, MyProperties.list contains one MyPojo entry, as previously defined. If the dev profile is enabled, however, the list still contains only one entry (with a name of my another name and a description of null). This configuration does not add a second MyPojo instance to the list, and it does not merge the items.

When a List is specified in multiple profiles, the one with the highest priority (and only that one) is used. Consider the following example:

Properties
my.list[0].name=my name
my.list[0].description=my description
my.list[1].name=another name
my.list[1].description=another description
#---
spring.config.activate.on-profile=dev
my.list[0].name=my another name
Yaml
my:
  list:
  - name: "my name"
    description: "my description"
  - name: "another name"
    description: "another description"
---
spring:
  config:
    activate:
      on-profile: "dev"
my:
  list:
  - name: "my another name"

In the preceding example, if the dev profile is active, MyProperties.list contains one MyPojo entry (with a name of my another name and a description of null). For YAML, both comma-separated lists and YAML lists can be used for completely overriding the contents of the list.

For Map properties, you can bind with property values drawn from multiple sources. However, for the same property in multiple sources, the one with the highest priority is used. The following example exposes a Map<String, MyPojo> from MyProperties:

Java
import java.util.LinkedHashMap;
import java.util.Map;

import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties("my")
public class MyProperties {

    private final Map<String, MyPojo> map = new LinkedHashMap<>();

    public Map<String, MyPojo> getMap() {
        return this.map;
    }

}
Kotlin
import org.springframework.boot.context.properties.ConfigurationProperties

@ConfigurationProperties("my")
class MyProperties {

    val map: Map<String, MyPojo> = LinkedHashMap()

}

Consider the following configuration:

Properties
my.map.key1.name=my name 1
my.map.key1.description=my description 1
#---
spring.config.activate.on-profile=dev
my.map.key1.name=dev name 1
my.map.key2.name=dev name 2
my.map.key2.description=dev description 2
Yaml
my:
  map:
    key1:
      name: "my name 1"
      description: "my description 1"
---
spring:
  config:
    activate:
      on-profile: "dev"
my:
  map:
    key1:
      name: "dev name 1"
    key2:
      name: "dev name 2"
      description: "dev description 2"

If the dev profile is not active, MyProperties.map contains one entry with key key1 (with a name of my name 1 and a description of my description 1). If the dev profile is enabled, however, map contains two entries with keys key1 (with a name of dev name 1 and a description of my description 1) and key2 (with a name of dev name 2 and a description of dev description 2).

The preceding merging rules apply to properties from all property sources, and not just files.
Properties Conversion

Spring Boot attempts to coerce the external application properties to the right type when it binds to the @ConfigurationProperties beans. If you need custom type conversion, you can provide a ConversionService bean (with a bean named conversionService) or custom property editors (through a CustomEditorConfigurer bean) or custom Converters (with bean definitions annotated as @ConfigurationPropertiesBinding).

As this bean is requested very early during the application lifecycle, make sure to limit the dependencies that your ConversionService is using. Typically, any dependency that you require may not be fully initialized at creation time. You may want to rename your custom ConversionService if it is not required for configuration keys coercion and only rely on custom converters qualified with @ConfigurationPropertiesBinding.
Converting Durations

Spring Boot has dedicated support for expressing durations. If you expose a java.time.Duration property, the following formats in application properties are available:

  • A regular long representation (using milliseconds as the default unit unless a @DurationUnit has been specified)

  • The standard ISO-8601 format used by java.time.Duration

  • A more readable format where the value and the unit are coupled (10s means 10 seconds)

Consider the following example:

Java
import java.time.Duration;
import java.time.temporal.ChronoUnit;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.convert.DurationUnit;

@ConfigurationProperties("my")
public class MyProperties {

    @DurationUnit(ChronoUnit.SECONDS)
    private Duration sessionTimeout = Duration.ofSeconds(30);

    private Duration readTimeout = Duration.ofMillis(1000);

    // getters / setters...

    public Duration getSessionTimeout() {
        return this.sessionTimeout;
    }

    public void setSessionTimeout(Duration sessionTimeout) {
        this.sessionTimeout = sessionTimeout;
    }

    public Duration getReadTimeout() {
        return this.readTimeout;
    }

    public void setReadTimeout(Duration readTimeout) {
        this.readTimeout = readTimeout;
    }

}
Kotlin
import org.springframework.boot.context.properties.ConfigurationProperties
import org.springframework.boot.convert.DurationUnit
import java.time.Duration
import java.time.temporal.ChronoUnit

@ConfigurationProperties("my")
class MyProperties {

    @DurationUnit(ChronoUnit.SECONDS)
    var sessionTimeout = Duration.ofSeconds(30)

    var readTimeout = Duration.ofMillis(1000)

}

To specify a session timeout of 30 seconds, 30, PT30S and 30s are all equivalent. A read timeout of 500ms can be specified in any of the following form: 500, PT0.5S and 500ms.

You can also use any of the supported units. These are:

  • ns for nanoseconds

  • us for microseconds

  • ms for milliseconds

  • s for seconds

  • m for minutes

  • h for hours

  • d for days

The default unit is milliseconds and can be overridden using @DurationUnit as illustrated in the sample above.

If you prefer to use constructor binding, the same properties can be exposed, as shown in the following example:

Java
import java.time.Duration;
import java.time.temporal.ChronoUnit;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.context.properties.ConstructorBinding;
import org.springframework.boot.context.properties.bind.DefaultValue;
import org.springframework.boot.convert.DurationUnit;

@ConfigurationProperties("my")
@ConstructorBinding
public class MyProperties {

    // fields...

    private final Duration sessionTimeout;

    private final Duration readTimeout;

    public MyProperties(@DurationUnit(ChronoUnit.SECONDS) @DefaultValue("30s") Duration sessionTimeout,
            @DefaultValue("1000ms") Duration readTimeout) {
        this.sessionTimeout = sessionTimeout;
        this.readTimeout = readTimeout;
    }

    // getters...

    public Duration getSessionTimeout() {
        return this.sessionTimeout;
    }

    public Duration getReadTimeout() {
        return this.readTimeout;
    }

}
Kotlin
import org.springframework.boot.context.properties.ConfigurationProperties
import org.springframework.boot.context.properties.ConstructorBinding
import org.springframework.boot.context.properties.bind.DefaultValue
import org.springframework.boot.convert.DurationUnit
import java.time.Duration
import java.time.temporal.ChronoUnit

@ConfigurationProperties("my")
@ConstructorBinding
class MyProperties(@param:DurationUnit(ChronoUnit.SECONDS) @param:DefaultValue("30s") val sessionTimeout: Duration,
        @param:DefaultValue("1000ms") val readTimeout: Duration)
If you are upgrading a Long property, make sure to define the unit (using @DurationUnit) if it is not milliseconds. Doing so gives a transparent upgrade path while supporting a much richer format.
Converting Periods

In addition to durations, Spring Boot can also work with java.time.Period type. The following formats can be used in application properties:

  • An regular int representation (using days as the default unit unless a @PeriodUnit has been specified)

  • The standard ISO-8601 format used by java.time.Period

  • A simpler format where the value and the unit pairs are coupled (1y3d means 1 year and 3 days)

The following units are supported with the simple format:

  • y for years

  • m for months

  • w for weeks

  • d for days

The java.time.Period type never actually stores the number of weeks, it is a shortcut that means “7 days”.
Converting Data Sizes

Spring Framework has a DataSize value type that expresses a size in bytes. If you expose a DataSize property, the following formats in application properties are available:

  • A regular long representation (using bytes as the default unit unless a @DataSizeUnit has been specified)

  • A more readable format where the value and the unit are coupled (10MB means 10 megabytes)

Consider the following example:

Java
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.convert.DataSizeUnit;
import org.springframework.util.unit.DataSize;
import org.springframework.util.unit.DataUnit;

@ConfigurationProperties("my")
public class MyProperties {

    @DataSizeUnit(DataUnit.MEGABYTES)
    private DataSize bufferSize = DataSize.ofMegabytes(2);

    private DataSize sizeThreshold = DataSize.ofBytes(512);

    // getters/setters...

    public DataSize getBufferSize() {
        return this.bufferSize;
    }

    public void setBufferSize(DataSize bufferSize) {
        this.bufferSize = bufferSize;
    }

    public DataSize getSizeThreshold() {
        return this.sizeThreshold;
    }

    public void setSizeThreshold(DataSize sizeThreshold) {
        this.sizeThreshold = sizeThreshold;
    }

}
Kotlin
import org.springframework.boot.context.properties.ConfigurationProperties
import org.springframework.boot.convert.DataSizeUnit
import org.springframework.util.unit.DataSize
import org.springframework.util.unit.DataUnit

@ConfigurationProperties("my")
class MyProperties {

    @DataSizeUnit(DataUnit.MEGABYTES)
    var bufferSize = DataSize.ofMegabytes(2)

    var sizeThreshold = DataSize.ofBytes(512)

}

To specify a buffer size of 10 megabytes, 10 and 10MB are equivalent. A size threshold of 256 bytes can be specified as 256 or 256B.

You can also use any of the supported units. These are:

  • B for bytes

  • KB for kilobytes

  • MB for megabytes

  • GB for gigabytes

  • TB for terabytes

The default unit is bytes and can be overridden using @DataSizeUnit as illustrated in the sample above.

If you prefer to use constructor binding, the same properties can be exposed, as shown in the following example:

Java
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.context.properties.ConstructorBinding;
import org.springframework.boot.context.properties.bind.DefaultValue;
import org.springframework.boot.convert.DataSizeUnit;
import org.springframework.util.unit.DataSize;
import org.springframework.util.unit.DataUnit;

@ConfigurationProperties("my")
@ConstructorBinding
public class MyProperties {

    // fields...

    private final DataSize bufferSize;

    private final DataSize sizeThreshold;

    public MyProperties(@DataSizeUnit(DataUnit.MEGABYTES) @DefaultValue("2MB") DataSize bufferSize,
            @DefaultValue("512B") DataSize sizeThreshold) {
        this.bufferSize = bufferSize;
        this.sizeThreshold = sizeThreshold;
    }

    // getters...

    public DataSize getBufferSize() {
        return this.bufferSize;
    }

    public DataSize getSizeThreshold() {
        return this.sizeThreshold;
    }

}
Kotlin
import org.springframework.boot.context.properties.ConfigurationProperties
import org.springframework.boot.context.properties.ConstructorBinding
import org.springframework.boot.context.properties.bind.DefaultValue
import org.springframework.boot.convert.DataSizeUnit
import org.springframework.util.unit.DataSize
import org.springframework.util.unit.DataUnit

@ConfigurationProperties("my")
@ConstructorBinding
class MyProperties(@param:DataSizeUnit(DataUnit.MEGABYTES) @param:DefaultValue("2MB") val bufferSize: DataSize,
        @param:DefaultValue("512B") val sizeThreshold: DataSize)
If you are upgrading a Long property, make sure to define the unit (using @DataSizeUnit) if it is not bytes. Doing so gives a transparent upgrade path while supporting a much richer format.
@ConfigurationProperties Validation

Spring Boot attempts to validate @ConfigurationProperties classes whenever they are annotated with Spring’s @Validated annotation. You can use JSR-303 javax.validation constraint annotations directly on your configuration class. To do so, ensure that a compliant JSR-303 implementation is on your classpath and then add constraint annotations to your fields, as shown in the following example:

Java
import java.net.InetAddress;

import javax.validation.constraints.NotNull;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.validation.annotation.Validated;

@ConfigurationProperties("my.service")
@Validated
public class MyProperties {

    @NotNull
    private InetAddress remoteAddress;

    // getters/setters...

    public InetAddress getRemoteAddress() {
        return this.remoteAddress;
    }

    public void setRemoteAddress(InetAddress remoteAddress) {
        this.remoteAddress = remoteAddress;
    }

}
Kotlin
import org.springframework.boot.context.properties.ConfigurationProperties
import org.springframework.validation.annotation.Validated
import java.net.InetAddress
import javax.validation.constraints.NotNull

@ConfigurationProperties("my.service")
@Validated
class MyProperties {

    var remoteAddress: @NotNull InetAddress? = null

}
You can also trigger validation by annotating the @Bean method that creates the configuration properties with @Validated.

To ensure that validation is always triggered for nested properties, even when no properties are found, the associated field must be annotated with @Valid. The following example builds on the preceding MyProperties example:

Java
import java.net.InetAddress;

import javax.validation.Valid;
import javax.validation.constraints.NotEmpty;
import javax.validation.constraints.NotNull;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.validation.annotation.Validated;

@ConfigurationProperties("my.service")
@Validated
public class MyProperties {

    @NotNull
    private InetAddress remoteAddress;

    @Valid
    private final Security security = new Security();

    // getters/setters...

    public InetAddress getRemoteAddress() {
        return this.remoteAddress;
    }

    public void setRemoteAddress(InetAddress remoteAddress) {
        this.remoteAddress = remoteAddress;
    }

    public Security getSecurity() {
        return this.security;
    }

    public static class Security {

        @NotEmpty
        private String username;

        // getters/setters...

        public String getUsername() {
            return this.username;
        }

        public void setUsername(String username) {
            this.username = username;
        }

    }

}
Kotlin
import org.springframework.boot.context.properties.ConfigurationProperties
import org.springframework.validation.annotation.Validated
import java.net.InetAddress
import javax.validation.Valid
import javax.validation.constraints.NotEmpty
import javax.validation.constraints.NotNull

@ConfigurationProperties("my.service")
@Validated
class MyProperties {

    var remoteAddress: @NotNull InetAddress? = null

    @Valid
    val security = Security()

    class Security {

        @NotEmpty
        var username: String? = null

    }

}

You can also add a custom Spring Validator by creating a bean definition called configurationPropertiesValidator. The @Bean method should be declared static. The configuration properties validator is created very early in the application’s lifecycle, and declaring the @Bean method as static lets the bean be created without having to instantiate the @Configuration class. Doing so avoids any problems that may be caused by early instantiation.

The spring-boot-actuator module includes an endpoint that exposes all @ConfigurationProperties beans. Point your web browser to /actuator/configprops or use the equivalent JMX endpoint. See the "Production ready features" section for details.
@ConfigurationProperties vs. @Value

The @Value annotation is a core container feature, and it does not provide the same features as type-safe configuration properties. The following table summarizes the features that are supported by @ConfigurationProperties and @Value:

Feature @ConfigurationProperties @Value

Relaxed binding

Yes

Limited (see note below)

Meta-data support

Yes

No

SpEL evaluation

No

Yes

If you do want to use @Value, we recommend that you refer to property names using their canonical form (kebab-case using only lowercase letters). This will allow Spring Boot to use the same logic as it does when relaxed binding @ConfigurationProperties.

For example, @Value("${demo.item-price}") will pick up demo.item-price and demo.itemPrice forms from the application.properties file, as well as DEMO_ITEMPRICE from the system environment. If you used @Value("${demo.itemPrice}") instead, demo.item-price and DEMO_ITEMPRICE would not be considered.

If you define a set of configuration keys for your own components, we recommend you group them in a POJO annotated with @ConfigurationProperties. Doing so will provide you with structured, type-safe object that you can inject into your own beans.

SpEL expressions from application property files are not processed at time of parsing these files and populating the environment. However, it is possible to write a SpEL expression in @Value. If the value of a property from an application property file is a SpEL expression, it will be evaluated when consumed through @Value.

7.3. Profiles

Spring Profiles provide a way to segregate parts of your application configuration and make it be available only in certain environments. Any @Component, @Configuration or @ConfigurationProperties can be marked with @Profile to limit when it is loaded, as shown in the following example:

Java
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Profile;

@Configuration(proxyBeanMethods = false)
@Profile("production")
public class ProductionConfiguration {

    // ...

}
Kotlin
import org.springframework.context.annotation.Configuration
import org.springframework.context.annotation.Profile

@Configuration(proxyBeanMethods = false)
@Profile("production")
class ProductionConfiguration {

    // ...

}
If @ConfigurationProperties beans are registered through @EnableConfigurationProperties instead of automatic scanning, the @Profile annotation needs to be specified on the @Configuration class that has the @EnableConfigurationProperties annotation. In the case where @ConfigurationProperties are scanned, @Profile can be specified on the @ConfigurationProperties class itself.

You can use a spring.profiles.active Environment property to specify which profiles are active. You can specify the property in any of the ways described earlier in this chapter. For example, you could include it in your application.properties, as shown in the following example:

Properties
spring.profiles.active=dev,hsqldb
Yaml
spring:
  profiles:
    active: "dev,hsqldb"

You could also specify it on the command line by using the following switch: --spring.profiles.active=dev,hsqldb.

If no profile is active, a default profile is enabled. The name of the default profile is default and it can be tuned using the spring.profiles.default Environment property, as shown in the following example:

Properties
spring.profiles.default=none
Yaml
spring:
  profiles:
    default: "none"

spring.profiles.active and spring.profiles.default can only be used in non-profile specific documents. This means they cannot be included in profile specific files or documents activated by spring.config.activate.on-profile.

For example, the second document configuration is invalid:

Properties
# this document is valid
spring.profiles.active=prod
#---
# this document is invalid
spring.config.activate.on-profile=prod
spring.profiles.active=metrics
Yaml
# this document is valid
spring:
  profiles:
    active: "prod"
---
# this document is invalid
spring:
  config:
    activate:
      on-profile: "prod"
  profiles:
    active: "metrics"

7.3.1. Adding Active Profiles

The spring.profiles.active property follows the same ordering rules as other properties: The highest PropertySource wins. This means that you can specify active profiles in application.properties and then replace them by using the command line switch.

Sometimes, it is useful to have properties that add to the active profiles rather than replace them. The spring.profiles.include property can be used to add active profiles on top of those activated by the spring.profiles.active property. The SpringApplication entry point also has a Java API for setting additional profiles. See the setAdditionalProfiles() method in SpringApplication.

For example, when an application with the following properties is run, the common and local profiles will be activated even when it runs using the --spring.profiles.active switch:

Properties
spring.profiles.include[0]=common
spring.profiles.include[1]=local
Yaml
spring:
  profiles:
    include:
      - "common"
      - "local"
Similar to spring.profiles.active, spring.profiles.include can only be used in non-profile specific documents. This means it cannot be included in profile specific files or documents activated by spring.config.activate.on-profile.

Profile groups, which are described in the next section can also be used to add active profiles if a given profile is active.

7.3.2. Profile Groups

Occasionally the profiles that you define and use in your application are too fine-grained and become cumbersome to use. For example, you might have proddb and prodmq profiles that you use to enable database and messaging features independently.

To help with this, Spring Boot lets you define profile groups. A profile group allows you to define a logical name for a related group of profiles.

For example, we can create a production group that consists of our proddb and prodmq profiles.

Properties
spring.profiles.group.production[0]=proddb
spring.profiles.group.production[1]=prodmq
Yaml
spring:
  profiles:
    group:
      production:
      - "proddb"
      - "prodmq"

Our application can now be started using --spring.profiles.active=production to active the production, proddb and prodmq profiles in one hit.

7.3.3. Programmatically Setting Profiles

You can programmatically set active profiles by calling SpringApplication.setAdditionalProfiles(…​) before your application runs. It is also possible to activate profiles by using Spring’s ConfigurableEnvironment interface.

7.3.4. Profile-specific Configuration Files

Profile-specific variants of both application.properties (or application.yaml) and files referenced through @ConfigurationProperties are considered as files and loaded. See "Profile Specific Files" for details.

7.4. Logging

Spring Boot uses Commons Logging for all internal logging but leaves the underlying log implementation open. Default configurations are provided for Java Util Logging, Log4J2, and Logback. In each case, loggers are pre-configured to use console output with optional file output also available.

By default, if you use the “Starters”, Logback is used for logging. Appropriate Logback routing is also included to ensure that dependent libraries that use Java Util Logging, Commons Logging, Log4J, or SLF4J all work correctly.

There are a lot of logging frameworks available for Java. Do not worry if the above list seems confusing. Generally, you do not need to change your logging dependencies and the Spring Boot defaults work just fine.
When you deploy your application to a servlet container or application server, logging performed with the Java Util Logging API is not routed into your application’s logs. This prevents logging performed by the container or other applications that have been deployed to it from appearing in your application’s logs.

7.4.1. Log Format

The default log output from Spring Boot resembles the following example:

2023-11-23 07:23:18.861  INFO 28351 --- [           main] o.s.b.d.f.logexample.MyApplication       : Starting MyApplication using Java 1.8.0_392 on myhost with PID 28351 (/opt/apps/myapp.jar started by myuser in /opt/apps/)
2023-11-23 07:23:18.868  INFO 28351 --- [           main] o.s.b.d.f.logexample.MyApplication       : No active profile set, falling back to 1 default profile: "default"
2023-11-23 07:23:20.194  INFO 28351 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2023-11-23 07:23:20.209  INFO 28351 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2023-11-23 07:23:20.209  INFO 28351 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.83]
2023-11-23 07:23:20.342  INFO 28351 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2023-11-23 07:23:20.342  INFO 28351 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1404 ms
2023-11-23 07:23:20.946  INFO 28351 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2023-11-23 07:23:20.962  INFO 28351 --- [           main] o.s.b.d.f.logexample.MyApplication       : Started MyApplication in 2.7 seconds (JVM running for 3.157)

The following items are output:

  • Date and Time: Millisecond precision and easily sortable.

  • Log Level: ERROR, WARN, INFO, DEBUG, or TRACE.

  • Process ID.

  • A --- separator to distinguish the start of actual log messages.

  • Thread name: Enclosed in square brackets (may be truncated for console output).

  • Logger name: This is usually the source class name (often abbreviated).

  • The log message.

Logback does not have a FATAL level. It is mapped to ERROR.

7.4.2. Console Output

The default log configuration echoes messages to the console as they are written. By default, ERROR-level, WARN-level, and INFO-level messages are logged. You can also enable a “debug” mode by starting your application with a --debug flag.

$ java -jar myapp.jar --debug
You can also specify debug=true in your application.properties.

When the debug mode is enabled, a selection of core loggers (embedded container, Hibernate, and Spring Boot) are configured to output more information. Enabling the debug mode does not configure your application to log all messages with DEBUG level.

Alternatively, you can enable a “trace” mode by starting your application with a --trace flag (or trace=true in your application.properties). Doing so enables trace logging for a selection of core loggers (embedded container, Hibernate schema generation, and the whole Spring portfolio).

Color-coded Output

If your terminal supports ANSI, color output is used to aid readability. You can set spring.output.ansi.enabled to a supported value to override the auto-detection.

Color coding is configured by using the %clr conversion word. In its simplest form, the converter colors the output according to the log level, as shown in the following example:

%clr(%5p)

The following table describes the mapping of log levels to colors:

Level Color

FATAL

Red

ERROR

Red

WARN

Yellow

INFO

Green

DEBUG

Green

TRACE

Green

Alternatively, you can specify the color or style that should be used by providing it as an option to the conversion. For example, to make the text yellow, use the following setting:

%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){yellow}

The following colors and styles are supported:

  • blue

  • cyan

  • faint

  • green

  • magenta

  • red

  • yellow

7.4.3. File Output

By default, Spring Boot logs only to the console and does not write log files. If you want to write log files in addition to the console output, you need to set a logging.file.name or logging.file.path property (for example, in your application.properties).

The following table shows how the logging.* properties can be used together:

Table 8. Logging properties
logging.file.name logging.file.path Example Description

(none)

(none)

Console only logging.

Specific file

(none)

my.log

Writes to the specified log file. Names can be an exact location or relative to the current directory.

(none)

Specific directory

/var/log

Writes spring.log to the specified directory. Names can be an exact location or relative to the current directory.

Log files rotate when they reach 10 MB and, as with console output, ERROR-level, WARN-level, and INFO-level messages are logged by default.

Logging properties are independent of the actual logging infrastructure. As a result, specific configuration keys (such as logback.configurationFile for Logback) are not managed by spring Boot.

7.4.4. File Rotation

If you are using the Logback, it is possible to fine-tune log rotation settings using your application.properties or application.yaml file. For all other logging system, you will need to configure rotation settings directly yourself (for example, if you use Log4J2 then you could add a log4j2.xml or log4j2-spring.xml file).

The following rotation policy properties are supported:

Name Description

logging.logback.rollingpolicy.file-name-pattern

The filename pattern used to create log archives.

logging.logback.rollingpolicy.clean-history-on-start

If log archive cleanup should occur when the application starts.

logging.logback.rollingpolicy.max-file-size

The maximum size of log file before it is archived.

logging.logback.rollingpolicy.total-size-cap

The maximum amount of size log archives can take before being deleted.

logging.logback.rollingpolicy.max-history

The maximum number of archive log files to keep (defaults to 7).

7.4.5. Log Levels

All the supported logging systems can have the logger levels set in the Spring Environment (for example, in application.properties) by using logging.level.<logger-name>=<level> where level is one of TRACE, DEBUG, INFO, WARN, ERROR, FATAL, or OFF. The root logger can be configured by using logging.level.root.

The following example shows potential logging settings in application.properties:

Properties
logging.level.root=warn
logging.level.org.springframework.web=debug
logging.level.org.hibernate=error
Yaml
logging:
  level:
    root: "warn"
    org.springframework.web: "debug"
    org.hibernate: "error"

It is also possible to set logging levels using environment variables. For example, LOGGING_LEVEL_ORG_SPRINGFRAMEWORK_WEB=DEBUG will set org.springframework.web to DEBUG.

The above approach will only work for package level logging. Since relaxed binding always converts environment variables to lowercase, it is not possible to configure logging for an individual class in this way. If you need to configure logging for a class, you can use the SPRING_APPLICATION_JSON variable.

7.4.6. Log Groups

It is often useful to be able to group related loggers together so that they can all be configured at the same time. For example, you might commonly change the logging levels for all Tomcat related loggers, but you can not easily remember top level packages.

To help with this, Spring Boot allows you to define logging groups in your Spring Environment. For example, here is how you could define a “tomcat” group by adding it to your application.properties:

Properties
logging.group.tomcat=org.apache.catalina,org.apache.coyote,org.apache.tomcat
Yaml
logging:
  group:
    tomcat: "org.apache.catalina,org.apache.coyote,org.apache.tomcat"

Once defined, you can change the level for all the loggers in the group with a single line:

Properties
logging.level.tomcat=trace
Yaml
logging:
  level:
    tomcat: "trace"

Spring Boot includes the following pre-defined logging groups that can be used out-of-the-box:

Name Loggers

web

org.springframework.core.codec, org.springframework.http, org.springframework.web, org.springframework.boot.actuate.endpoint.web, org.springframework.boot.web.servlet.ServletContextInitializerBeans

sql

org.springframework.jdbc.core, org.hibernate.SQL, org.jooq.tools.LoggerListener

7.4.7. Using a Log Shutdown Hook

In order to release logging resources when your application terminates, a shutdown hook that will trigger log system cleanup when the JVM exits is provided. This shutdown hook is registered automatically unless your application is deployed as a war file. If your application has complex context hierarchies the shutdown hook may not meet your needs. If it does not, disable the shutdown hook and investigate the options provided directly by the underlying logging system. For example, Logback offers context selectors which allow each Logger to be created in its own context. You can use the logging.register-shutdown-hook property to disable the shutdown hook. Setting it to false will disable the registration. You can set the property in your application.properties or application.yaml file:

Properties
logging.register-shutdown-hook=false
Yaml
logging:
  register-shutdown-hook: false

7.4.8. Custom Log Configuration

The various logging systems can be activated by including the appropriate libraries on the classpath and can be further customized by providing a suitable configuration file in the root of the classpath or in a location specified by the following Spring Environment property: logging.config.

You can force Spring Boot to use a particular logging system by using the org.springframework.boot.logging.LoggingSystem system property. The value should be the fully qualified class name of a LoggingSystem implementation. You can also disable Spring Boot’s logging configuration entirely by using a value of none.

Since logging is initialized before the ApplicationContext is created, it is not possible to control logging from @PropertySources in Spring @Configuration files. The only way to change the logging system or disable it entirely is through System properties.

Depending on your logging system, the following files are loaded:

Logging System Customization

Logback

logback-spring.xml, logback-spring.groovy, logback.xml, or logback.groovy

Log4j2

log4j2-spring.xml or log4j2.xml

JDK (Java Util Logging)

logging.properties

When possible, we recommend that you use the -spring variants for your logging configuration (for example, logback-spring.xml rather than logback.xml). If you use standard configuration locations, Spring cannot completely control log initialization.
There are known classloading issues with Java Util Logging that cause problems when running from an 'executable jar'. We recommend that you avoid it when running from an 'executable jar' if at all possible.

To help with the customization, some other properties are transferred from the Spring Environment to System properties. This allows the properties to be consumed by logging system configuration. For example, setting logging.file.name in application.properties or LOGGING_FILE_NAME as an environment variable will result in the LOG_FILE System property being set. The properties that are transferred are described in the following table:

Spring Environment System Property Comments

logging.exception-conversion-word

LOG_EXCEPTION_CONVERSION_WORD

The conversion word used when logging exceptions.

logging.file.name

LOG_FILE

If defined, it is used in the default log configuration.

logging.file.path

LOG_PATH

If defined, it is used in the default log configuration.

logging.pattern.console

CONSOLE_LOG_PATTERN

The log pattern to use on the console (stdout).

logging.pattern.dateformat

LOG_DATEFORMAT_PATTERN

Appender pattern for log date format.

logging.charset.console

CONSOLE_LOG_CHARSET

The charset to use for console logging.

logging.pattern.file

FILE_LOG_PATTERN

The log pattern to use in a file (if LOG_FILE is enabled).

logging.charset.file

FILE_LOG_CHARSET

The charset to use for file logging (if LOG_FILE is enabled).

logging.pattern.level

LOG_LEVEL_PATTERN

The format to use when rendering the log level (default %5p).

PID

PID

The current process ID (discovered if possible and when not already defined as an OS environment variable).

If you use Logback, the following properties are also transferred:

Spring Environment System Property Comments

logging.logback.rollingpolicy.file-name-pattern

LOGBACK_ROLLINGPOLICY_FILE_NAME_PATTERN

Pattern for rolled-over log file names (default ${LOG_FILE}.%d{yyyy-MM-dd}.%i.gz).

logging.logback.rollingpolicy.clean-history-on-start

LOGBACK_ROLLINGPOLICY_CLEAN_HISTORY_ON_START

Whether to clean the archive log files on startup.

logging.logback.rollingpolicy.max-file-size

LOGBACK_ROLLINGPOLICY_MAX_FILE_SIZE

Maximum log file size.

logging.logback.rollingpolicy.total-size-cap

LOGBACK_ROLLINGPOLICY_TOTAL_SIZE_CAP

Total size of log backups to be kept.

logging.logback.rollingpolicy.max-history

LOGBACK_ROLLINGPOLICY_MAX_HISTORY

Maximum number of archive log files to keep.

All the supported logging systems can consult System properties when parsing their configuration files. See the default configurations in spring-boot.jar for examples:

If you want to use a placeholder in a logging property, you should use Spring Boot’s syntax and not the syntax of the underlying framework. Notably, if you use Logback, you should use : as the delimiter between a property name and its default value and not use :-.

You can add MDC and other ad-hoc content to log lines by overriding only the LOG_LEVEL_PATTERN (or logging.pattern.level with Logback). For example, if you use logging.pattern.level=user:%X{user} %5p, then the default log format contains an MDC entry for "user", if it exists, as shown in the following example.

2019-08-30 12:30:04.031 user:someone INFO 22174 --- [  nio-8080-exec-0] demo.Controller
Handling authenticated request

7.4.9. Logback Extensions

Spring Boot includes a number of extensions to Logback that can help with advanced configuration. You can use these extensions in your logback-spring.xml configuration file.

Because the standard logback.xml configuration file is loaded too early, you cannot use extensions in it. You need to either use logback-spring.xml or define a logging.config property.
The extensions cannot be used with Logback’s configuration scanning. If you attempt to do so, making changes to the configuration file results in an error similar to one of the following being logged:
ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProperty], current ElementPath is [[configuration][springProperty]]
ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProfile], current ElementPath is [[configuration][springProfile]]
Profile-specific Configuration

The <springProfile> tag lets you optionally include or exclude sections of configuration based on the active Spring profiles. Profile sections are supported anywhere within the <configuration> element. Use the name attribute to specify which profile accepts the configuration. The <springProfile> tag can contain a profile name (for example staging) or a profile expression. A profile expression allows for more complicated profile logic to be expressed, for example production & (eu-central | eu-west). Check the reference guide for more details. The following listing shows three sample profiles:

<springProfile name="staging">
    <!-- configuration to be enabled when the "staging" profile is active -->
</springProfile>

<springProfile name="dev | staging">
    <!-- configuration to be enabled when the "dev" or "staging" profiles are active -->
</springProfile>

<springProfile name="!production">
    <!-- configuration to be enabled when the "production" profile is not active -->
</springProfile>
Environment Properties

The <springProperty> tag lets you expose properties from the Spring Environment for use within Logback. Doing so can be useful if you want to access values from your application.properties file in your Logback configuration. The tag works in a similar way to Logback’s standard <property> tag. However, rather than specifying a direct value, you specify the source of the property (from the Environment). If you need to store the property somewhere other than in local scope, you can use the scope attribute. If you need a fallback value (in case the property is not set in the Environment), you can use the defaultValue attribute. The following example shows how to expose properties for use within Logback:

<springProperty scope="context" name="fluentHost" source="myapp.fluentd.host"
        defaultValue="localhost"/>
<appender name="FLUENT" class="ch.qos.logback.more.appenders.DataFluentAppender">
    <remoteHost>${fluentHost}</remoteHost>
    ...
</appender>
The source must be specified in kebab case (such as my.property-name). However, properties can be added to the Environment by using the relaxed rules.

7.5. Internationalization

Spring Boot supports localized messages so that your application can cater to users of different language preferences. By default, Spring Boot looks for the presence of a messages resource bundle at the root of the classpath.

The auto-configuration applies when the default properties file for the configured resource bundle is available (messages.properties by default). If your resource bundle contains only language-specific properties files, you are required to add the default. If no properties file is found that matches any of the configured base names, there will be no auto-configured MessageSource.

The basename of the resource bundle as well as several other attributes can be configured using the spring.messages namespace, as shown in the following example:

Properties
spring.messages.basename=messages,config.i18n.messages
spring.messages.fallback-to-system-locale=false
Yaml
spring:
  messages:
    basename: "messages,config.i18n.messages"
    fallback-to-system-locale: false
spring.messages.basename supports comma-separated list of locations, either a package qualifier or a resource resolved from the classpath root.

See MessageSourceProperties for more supported options.

7.6. Aspect-Oriented Programming

Spring Boot provides auto-configuration for aspect-oriented programming (AOP). You can learn more about AOP with Spring in the Spring Framework reference documentation.

By default, Spring Boot’s auto-configuration configures Spring AOP to use CGLib proxies. To use JDK proxies instead, set configprop:spring.aop.proxy-target-class to false.

If AspectJ is on the classpath, Spring Boot’s auto-configuration will automatically enable AspectJ auto proxy such that @EnableAspectJAutoProxy is not required.

7.7. JSON

Spring Boot provides integration with three JSON mapping libraries:

  • Gson

  • Jackson

  • JSON-B

Jackson is the preferred and default library.

7.7.1. Jackson

Auto-configuration for Jackson is provided and Jackson is part of spring-boot-starter-json. When Jackson is on the classpath an ObjectMapper bean is automatically configured. Several configuration properties are provided for customizing the configuration of the ObjectMapper.

Custom Serializers and Deserializers

If you use Jackson to serialize and deserialize JSON data, you might want to write your own JsonSerializer and JsonDeserializer classes. Custom serializers are usually registered with Jackson through a module, but Spring Boot provides an alternative @JsonComponent annotation that makes it easier to directly register Spring Beans.

You can use the @JsonComponent annotation directly on JsonSerializer, JsonDeserializer or KeyDeserializer implementations. You can also use it on classes that contain serializers/deserializers as inner classes, as shown in the following example:

Java
import java.io.IOException;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.ObjectCodec;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;

import org.springframework.boot.jackson.JsonComponent;

@JsonComponent
public class MyJsonComponent {

    public static class Serializer extends JsonSerializer<MyObject> {

        @Override
        public void serialize(MyObject value, JsonGenerator jgen, SerializerProvider serializers) throws IOException {
            jgen.writeStartObject();
            jgen.writeStringField("name", value.getName());
            jgen.writeNumberField("age", value.getAge());
            jgen.writeEndObject();
        }

    }

    public static class Deserializer extends JsonDeserializer<MyObject> {

        @Override
        public MyObject deserialize(JsonParser jsonParser, DeserializationContext ctxt) throws IOException {
            ObjectCodec codec = jsonParser.getCodec();
            JsonNode tree = codec.readTree(jsonParser);
            String name = tree.get("name").textValue();
            int age = tree.get("age").intValue();
            return new MyObject(name, age);
        }

    }

}
Kotlin
import com.fasterxml.jackson.core.JsonGenerator
import com.fasterxml.jackson.core.JsonParser
import com.fasterxml.jackson.core.JsonProcessingException
import com.fasterxml.jackson.databind.DeserializationContext
import com.fasterxml.jackson.databind.JsonDeserializer
import com.fasterxml.jackson.databind.JsonNode
import com.fasterxml.jackson.databind.JsonSerializer
import com.fasterxml.jackson.databind.SerializerProvider
import org.springframework.boot.jackson.JsonComponent
import java.io.IOException
import kotlin.jvm.Throws

@JsonComponent
class MyJsonComponent {

    class Serializer : JsonSerializer<MyObject>() {
        @Throws(IOException::class)
        override fun serialize(value: MyObject, jgen: JsonGenerator, serializers: SerializerProvider) {
            jgen.writeStartObject()
            jgen.writeStringField("name", value.name)
            jgen.writeNumberField("age", value.age)
            jgen.writeEndObject()
        }
    }

    class Deserializer : JsonDeserializer<MyObject>() {
        @Throws(IOException::class, JsonProcessingException::class)
        override fun deserialize(jsonParser: JsonParser, ctxt: DeserializationContext): MyObject {
            val codec = jsonParser.codec
            val tree = codec.readTree<JsonNode>(jsonParser)
            val name = tree["name"].textValue()
            val age = tree["age"].intValue()
            return MyObject(name, age)
        }
    }

}

All @JsonComponent beans in the ApplicationContext are automatically registered with Jackson. Because @JsonComponent is meta-annotated with @Component, the usual component-scanning rules apply.

Spring Boot also provides JsonObjectSerializer and JsonObjectDeserializer base classes that provide useful alternatives to the standard Jackson versions when serializing objects. See JsonObjectSerializer and JsonObjectDeserializer in the Javadoc for details.

The example above can be rewritten to use JsonObjectSerializer/JsonObjectDeserializer as follows:

Java
import java.io.IOException;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.ObjectCodec;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.SerializerProvider;

import org.springframework.boot.jackson.JsonComponent;
import org.springframework.boot.jackson.JsonObjectDeserializer;
import org.springframework.boot.jackson.JsonObjectSerializer;

@JsonComponent
public class MyJsonComponent {

    public static class Serializer extends JsonObjectSerializer<MyObject> {

        @Override
        protected void serializeObject(MyObject value, JsonGenerator jgen, SerializerProvider provider)
                throws IOException {
            jgen.writeStringField("name", value.getName());
            jgen.writeNumberField("age", value.getAge());
        }

    }

    public static class Deserializer extends JsonObjectDeserializer<MyObject> {

        @Override
        protected MyObject deserializeObject(JsonParser jsonParser, DeserializationContext context, ObjectCodec codec,
                JsonNode tree) throws IOException {
            String name = nullSafeValue(tree.get("name"), String.class);
            int age = nullSafeValue(tree.get("age"), Integer.class);
            return new MyObject(name, age);
        }

    }

}
Kotlin
`object`

import com.fasterxml.jackson.core.JsonGenerator
import com.fasterxml.jackson.core.JsonParser
import com.fasterxml.jackson.core.ObjectCodec
import com.fasterxml.jackson.databind.DeserializationContext
import com.fasterxml.jackson.databind.JsonNode
import com.fasterxml.jackson.databind.SerializerProvider
import org.springframework.boot.jackson.JsonComponent
import org.springframework.boot.jackson.JsonObjectDeserializer
import org.springframework.boot.jackson.JsonObjectSerializer
import java.io.IOException
import kotlin.jvm.Throws

@JsonComponent
class MyJsonComponent {

    class Serializer : JsonObjectSerializer<MyObject>() {
        @Throws(IOException::class)
        override fun serializeObject(value: MyObject, jgen: JsonGenerator, provider: SerializerProvider) {
            jgen.writeStringField("name", value.name)
            jgen.writeNumberField("age", value.age)
        }
    }

    class Deserializer : JsonObjectDeserializer<MyObject>() {
        @Throws(IOException::class)
        override fun deserializeObject(jsonParser: JsonParser, context: DeserializationContext,
                codec: ObjectCodec, tree: JsonNode): MyObject {
            val name = nullSafeValue(tree["name"], String::class.java)
            val age = nullSafeValue(tree["age"], Int::class.java)
            return MyObject(name, age)
        }
    }

}
Mixins

Jackson has support for mixins that can be used to mix additional annotations into those already declared on a target class. Spring Boot’s Jackson auto-configuration will scan your application’s packages for classes annotated with @JsonMixin and register them with the auto-configured ObjectMapper. The registration is performed by Spring Boot’s JsonMixinModule.

7.7.2. Gson

Auto-configuration for Gson is provided. When Gson is on the classpath a Gson bean is automatically configured. Several spring.gson.* configuration properties are provided for customizing the configuration. To take more control, one or more GsonBuilderCustomizer beans can be used.

7.7.3. JSON-B

Auto-configuration for JSON-B is provided. When the JSON-B API and an implementation are on the classpath a Jsonb bean will be automatically configured. The preferred JSON-B implementation is Apache Johnzon for which dependency management is provided.

7.8. Task Execution and Scheduling

In the absence of an Executor bean in the context, Spring Boot auto-configures a ThreadPoolTaskExecutor with sensible defaults that can be automatically associated to asynchronous task execution (@EnableAsync) and Spring MVC asynchronous request processing.

If you have defined a custom Executor in the context, regular task execution (that is @EnableAsync) will use it transparently but the Spring MVC support will not be configured as it requires an AsyncTaskExecutor implementation (named applicationTaskExecutor). Depending on your target arrangement, you could change your Executor into a ThreadPoolTaskExecutor or define both a ThreadPoolTaskExecutor and an AsyncConfigurer wrapping your custom Executor.

The auto-configured TaskExecutorBuilder allows you to easily create instances that reproduce what the auto-configuration does by default.

The thread pool uses 8 core threads that can grow and shrink according to the load. Those default settings can be fine-tuned using the spring.task.execution namespace, as shown in the following example:

Properties
spring.task.execution.pool.max-size=16
spring.task.execution.pool.queue-capacity=100
spring.task.execution.pool.keep-alive=10s
Yaml
spring:
  task:
    execution:
      pool:
        max-size: 16
        queue-capacity: 100
        keep-alive: "10s"

This changes the thread pool to use a bounded queue so that when the queue is full (100 tasks), the thread pool increases to maximum 16 threads. Shrinking of the pool is more aggressive as threads are reclaimed when they are idle for 10 seconds (rather than 60 seconds by default).

A ThreadPoolTaskScheduler can also be auto-configured if need to be associated to scheduled task execution (using @EnableScheduling for instance). The thread pool uses one thread by default and its settings can be fine-tuned using the spring.task.scheduling namespace, as shown in the following example:

Properties
spring.task.scheduling.thread-name-prefix=scheduling-
spring.task.scheduling.pool.size=2
Yaml
spring:
  task:
    scheduling:
      thread-name-prefix: "scheduling-"
      pool:
        size: 2

Both a TaskExecutorBuilder bean and a TaskSchedulerBuilder bean are made available in the context if a custom executor or scheduler needs to be created.

7.9. Testing

Spring Boot provides a number of utilities and annotations to help when testing your application. Test support is provided by two modules: spring-boot-test contains core items, and spring-boot-test-autoconfigure supports auto-configuration for tests.

Most developers use the spring-boot-starter-test “Starter”, which imports both Spring Boot test modules as well as JUnit Jupiter, AssertJ, Hamcrest, and a number of other useful libraries.

If you have tests that use JUnit 4, JUnit 5’s vintage engine can be used to run them. To use the vintage engine, add a dependency on junit-vintage-engine, as shown in the following example:

<dependency>
    <groupId>org.junit.vintage</groupId>
    <artifactId>junit-vintage-engine</artifactId>
    <scope>test</scope>
    <exclusions>
        <exclusion>
            <groupId>org.hamcrest</groupId>
            <artifactId>hamcrest-core</artifactId>
        </exclusion>
    </exclusions>
</dependency>

hamcrest-core is excluded in favor of org.hamcrest:hamcrest that is part of spring-boot-starter-test.

7.9.1. Test Scope Dependencies

The spring-boot-starter-test “Starter” (in the test scope) contains the following provided libraries:

  • JUnit 5: The de-facto standard for unit testing Java applications.

  • Spring Test & Spring Boot Test: Utilities and integration test support for Spring Boot applications.

  • AssertJ: A fluent assertion library.

  • Hamcrest: A library of matcher objects (also known as constraints or predicates).

  • Mockito: A Java mocking framework.

  • JSONassert: An assertion library for JSON.

  • JsonPath: XPath for JSON.

We generally find these common libraries to be useful when writing tests. If these libraries do not suit your needs, you can add additional test dependencies of your own.

7.9.2. Testing Spring Applications

One of the major advantages of dependency injection is that it should make your code easier to unit test. You can instantiate objects by using the new operator without even involving Spring. You can also use mock objects instead of real dependencies.

Often, you need to move beyond unit testing and start integration testing (with a Spring ApplicationContext). It is useful to be able to perform integration testing without requiring deployment of your application or needing to connect to other infrastructure.

The Spring Framework includes a dedicated test module for such integration testing. You can declare a dependency directly to org.springframework:spring-test or use the spring-boot-starter-test “Starter” to pull it in transitively.

If you have not used the spring-test module before, you should start by reading the relevant section of the Spring Framework reference documentation.

7.9.3. Testing Spring Boot Applications

A Spring Boot application is a Spring ApplicationContext, so nothing very special has to be done to test it beyond what you would normally do with a vanilla Spring context.

External properties, logging, and other features of Spring Boot are installed in the context by default only if you use SpringApplication to create it.

Spring Boot provides a @SpringBootTest annotation, which can be used as an alternative to the standard spring-test @ContextConfiguration annotation when you need Spring Boot features. The annotation works by creating the ApplicationContext used in your tests through SpringApplication. In addition to @SpringBootTest a number of other annotations are also provided for testing more specific slices of an application.

If you are using JUnit 4, do not forget to also add @RunWith(SpringRunner.class) to your test, otherwise the annotations will be ignored. If you are using JUnit 5, there is no need to add the equivalent @ExtendWith(SpringExtension.class) as @SpringBootTest and the other @…​Test annotations are already annotated with it.

By default, @SpringBootTest will not start a server. You can use the webEnvironment attribute of @SpringBootTest to further refine how your tests run:

  • MOCK(Default) : Loads a web ApplicationContext and provides a mock web environment. Embedded servers are not started when using this annotation. If a web environment is not available on your classpath, this mode transparently falls back to creating a regular non-web ApplicationContext. It can be used in conjunction with @AutoConfigureMockMvc or @AutoConfigureWebTestClient for mock-based testing of your web application.

  • RANDOM_PORT: Loads a WebServerApplicationContext and provides a real web environment. Embedded servers are started and listen on a random port.

  • DEFINED_PORT: Loads a WebServerApplicationContext and provides a real web environment. Embedded servers are started and listen on a defined port (from your application.properties) or on the default port of 8080.

  • NONE: Loads an ApplicationContext by using SpringApplication but does not provide any web environment (mock or otherwise).

If your test is @Transactional, it rolls back the transaction at the end of each test method by default. However, as using this arrangement with either RANDOM_PORT or DEFINED_PORT implicitly provides a real servlet environment, the HTTP client and server run in separate threads and, thus, in separate transactions. Any transaction initiated on the server does not roll back in this case.
@SpringBootTest with webEnvironment = WebEnvironment.RANDOM_PORT will also start the management server on a separate random port if your application uses a different port for the management server.
Detecting Web Application Type

If Spring MVC is available, a regular MVC-based application context is configured. If you have only Spring WebFlux, we will detect that and configure a WebFlux-based application context instead.

If both are present, Spring MVC takes precedence. If you want to test a reactive web application in this scenario, you must set the spring.main.web-application-type property:

Java
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest(properties = "spring.main.web-application-type=reactive")
class MyWebFluxTests {

    // ...

}
Kotlin
import org.springframework.boot.test.context.SpringBootTest

@SpringBootTest(properties = ["spring.main.web-application-type=reactive"])
class MyWebFluxTests {

    // ...

}
Detecting Test Configuration

If you are familiar with the Spring Test Framework, you may be used to using @ContextConfiguration(classes=…​) in order to specify which Spring @Configuration to load. Alternatively, you might have often used nested @Configuration classes within your test.

When testing Spring Boot applications, this is often not required. Spring Boot’s @*Test annotations search for your primary configuration automatically whenever you do not explicitly define one.

The search algorithm works up from the package that contains the test until it finds a class annotated with @SpringBootApplication or @SpringBootConfiguration. As long as you structured your code in a sensible way, your main configuration is usually found.

If you use a test annotation to test a more specific slice of your application, you should avoid adding configuration settings that are specific to a particular area on the main method’s application class.

The underlying component scan configuration of @SpringBootApplication defines exclude filters that are used to make sure slicing works as expected. If you are using an explicit @ComponentScan directive on your @SpringBootApplication-annotated class, be aware that those filters will be disabled. If you are using slicing, you should define them again.

If you want to customize the primary configuration, you can use a nested @TestConfiguration class. Unlike a nested @Configuration class, which would be used instead of your application’s primary configuration, a nested @TestConfiguration class is used in addition to your application’s primary configuration.

Spring’s test framework caches application contexts between tests. Therefore, as long as your tests share the same configuration (no matter how it is discovered), the potentially time-consuming process of loading the context happens only once.
Excluding Test Configuration

If your application uses component scanning (for example, if you use @SpringBootApplication or @ComponentScan), you may find top-level configuration classes that you created only for specific tests accidentally get picked up everywhere.

As we have seen earlier, @TestConfiguration can be used on an inner class of a test to customize the primary configuration. @TestConfiguration can also be used on a top-level class. Doing so indicates that the class should not be picked up by scanning. You can then import the class explicitly where it is required, as shown in the following example:

Java
import org.junit.jupiter.api.Test;

import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.context.annotation.Import;

@SpringBootTest
@Import(MyTestsConfiguration.class)
class MyTests {

    @Test
    void exampleTest() {
        // ...
    }

}
Kotlin
import org.junit.jupiter.api.Test
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.context.annotation.Import

@SpringBootTest
@Import(MyTestsConfiguration::class)
class MyTests {

    @Test
    fun exampleTest() {
        // ...
    }

}
If you directly use @ComponentScan (that is, not through @SpringBootApplication) you need to register the TypeExcludeFilter with it. See the Javadoc for details.
An imported @TestConfiguration is processed earlier than an inner-class @TestConfiguration and an imported @TestConfiguration will be processed before any configuration found through component scanning. Generally speaking, this difference in ordering has no noticeable effect but it is something to be aware of if you’re relying on bean overriding.
Using Application Arguments

If your application expects arguments, you can have @SpringBootTest inject them using the args attribute.

Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.test.context.SpringBootTest;

import static org.assertj.core.api.Assertions.assertThat;

@SpringBootTest(args = "--app.test=one")
class MyApplicationArgumentTests {

    @Test
    void applicationArgumentsPopulated(@Autowired ApplicationArguments args) {
        assertThat(args.getOptionNames()).containsOnly("app.test");
        assertThat(args.getOptionValues("app.test")).containsOnly("one");
    }

}
Kotlin
import org.assertj.core.api.Assertions.assertThat
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.ApplicationArguments
import org.springframework.boot.test.context.SpringBootTest

@SpringBootTest(args = ["--app.test=one"])
class MyApplicationArgumentTests {

    @Test
    fun applicationArgumentsPopulated(@Autowired args: ApplicationArguments) {
        assertThat(args.optionNames).containsOnly("app.test")
        assertThat(args.getOptionValues("app.test")).containsOnly("one")
    }

}
Testing With a Mock Environment

By default, @SpringBootTest does not start the server but instead sets up a mock environment for testing web endpoints.

With Spring MVC, we can query our web endpoints using MockMvc or WebTestClient, as shown in the following example:

Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.web.reactive.server.WebTestClient;
import org.springframework.test.web.servlet.MockMvc;

import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

@SpringBootTest
@AutoConfigureMockMvc
class MyMockMvcTests {

    @Test
    void testWithMockMvc(@Autowired MockMvc mvc) throws Exception {
        mvc.perform(get("/")).andExpect(status().isOk()).andExpect(content().string("Hello World"));
    }

    // If Spring WebFlux is on the classpath, you can drive MVC tests with a WebTestClient
    @Test
    void testWithWebTestClient(@Autowired WebTestClient webClient) {
        webClient
                .get().uri("/")
                .exchange()
                .expectStatus().isOk()
                .expectBody(String.class).isEqualTo("Hello World");
    }

}
Kotlin
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.test.web.reactive.server.WebTestClient
import org.springframework.test.web.reactive.server.expectBody
import org.springframework.test.web.servlet.MockMvc
import org.springframework.test.web.servlet.request.MockMvcRequestBuilders
import org.springframework.test.web.servlet.result.MockMvcResultMatchers

@SpringBootTest
@AutoConfigureMockMvc
class MyMockMvcTests {

    @Test
    fun testWithMockMvc(@Autowired mvc: MockMvc) {
        mvc.perform(MockMvcRequestBuilders.get("/")).andExpect(MockMvcResultMatchers.status().isOk)
            .andExpect(MockMvcResultMatchers.content().string("Hello World"))
    }

    // If Spring WebFlux is on the classpath, you can drive MVC tests with a WebTestClient

    @Test
    fun testWithWebTestClient(@Autowired webClient: WebTestClient) {
        webClient
            .get().uri("/")
            .exchange()
            .expectStatus().isOk
            .expectBody<String>().isEqualTo("Hello World")
    }

}
If you want to focus only on the web layer and not start a complete ApplicationContext, consider using @WebMvcTest instead.

With Spring WebFlux endpoints, you can use WebTestClient as shown in the following example:

Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.reactive.AutoConfigureWebTestClient;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.web.reactive.server.WebTestClient;

@SpringBootTest
@AutoConfigureWebTestClient
class MyMockWebTestClientTests {

    @Test
    void exampleTest(@Autowired WebTestClient webClient) {
        webClient
            .get().uri("/")
            .exchange()
            .expectStatus().isOk()
            .expectBody(String.class).isEqualTo("Hello World");
    }

}
Kotlin
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.web.reactive.AutoConfigureWebTestClient
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.test.web.reactive.server.WebTestClient
import org.springframework.test.web.reactive.server.expectBody

@SpringBootTest
@AutoConfigureWebTestClient
class MyMockWebTestClientTests {

    @Test
    fun exampleTest(@Autowired webClient: WebTestClient) {
        webClient
            .get().uri("/")
            .exchange()
            .expectStatus().isOk
            .expectBody<String>().isEqualTo("Hello World")
    }

}

Testing within a mocked environment is usually faster than running with a full servlet container. However, since mocking occurs at the Spring MVC layer, code that relies on lower-level servlet container behavior cannot be directly tested with MockMvc.

For example, Spring Boot’s error handling is based on the “error page” support provided by the servlet container. This means that, whilst you can test your MVC layer throws and handles exceptions as expected, you cannot directly test that a specific custom error page is rendered. If you need to test these lower-level concerns, you can start a fully running server as described in the next section.

Testing With a Running Server

If you need to start a full running server, we recommend that you use random ports. If you use @SpringBootTest(webEnvironment=WebEnvironment.RANDOM_PORT), an available port is picked at random each time your test runs.

The @LocalServerPort annotation can be used to inject the actual port used into your test. For convenience, tests that need to make REST calls to the started server can additionally @Autowire a WebTestClient, which resolves relative links to the running server and comes with a dedicated API for verifying responses, as shown in the following example:

Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.test.web.reactive.server.WebTestClient;

@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MyRandomPortWebTestClientTests {

    @Test
    void exampleTest(@Autowired WebTestClient webClient) {
        webClient
            .get().uri("/")
            .exchange()
            .expectStatus().isOk()
            .expectBody(String.class).isEqualTo("Hello World");
    }

}
Kotlin
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment
import org.springframework.test.web.reactive.server.WebTestClient
import org.springframework.test.web.reactive.server.expectBody

@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MyRandomPortWebTestClientTests {

    @Test
    fun exampleTest(@Autowired webClient: WebTestClient) {
        webClient
            .get().uri("/")
            .exchange()
            .expectStatus().isOk
            .expectBody<String>().isEqualTo("Hello World")
    }

}
WebTestClient can also used with a mock environment, removing the need for a running server, by annotating your test class with @AutoConfigureWebTestClient.

This setup requires spring-webflux on the classpath. If you can not or will not add webflux, Spring Boot also provides a TestRestTemplate facility:

Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.boot.test.web.client.TestRestTemplate;

import static org.assertj.core.api.Assertions.assertThat;

@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MyRandomPortTestRestTemplateTests {

    @Test
    void exampleTest(@Autowired TestRestTemplate restTemplate) {
        String body = restTemplate.getForObject("/", String.class);
        assertThat(body).isEqualTo("Hello World");
    }

}
Kotlin
import org.assertj.core.api.Assertions.assertThat
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment
import org.springframework.boot.test.web.client.TestRestTemplate

@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MyRandomPortTestRestTemplateTests {

    @Test
    fun exampleTest(@Autowired restTemplate: TestRestTemplate) {
        val body = restTemplate.getForObject("/", String::class.java)
        assertThat(body).isEqualTo("Hello World")
    }

}
Customizing WebTestClient

To customize the WebTestClient bean, configure a WebTestClientBuilderCustomizer bean. Any such beans are called with the WebTestClient.Builder that is used to create the WebTestClient.

Using JMX

As the test context framework caches context, JMX is disabled by default to prevent identical components to register on the same domain. If such test needs access to an MBeanServer, consider marking it dirty as well:

Java
import javax.management.MBeanServer;

import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.annotation.DirtiesContext;

import static org.assertj.core.api.Assertions.assertThat;

@SpringBootTest(properties = "spring.jmx.enabled=true")
@DirtiesContext
class MyJmxTests {

    @Autowired
    private MBeanServer mBeanServer;

    @Test
    void exampleTest() {
        assertThat(this.mBeanServer.getDomains()).contains("java.lang");
        // ...
    }

}
Kotlin
import org.assertj.core.api.Assertions.assertThat
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.test.annotation.DirtiesContext
import javax.management.MBeanServer

@SpringBootTest(properties = ["spring.jmx.enabled=true"])
@DirtiesContext
class MyJmxTests(@Autowired val mBeanServer: MBeanServer) {

    @Test
    fun exampleTest() {
        assertThat(mBeanServer.domains).contains("java.lang")
        // ...
    }

}
Using Metrics

Regardless of your classpath, meter registries, except the in-memory backed, are not auto-configured when using @SpringBootTest.

If you need to export metrics to a different backend as part of an integration test, annotate it with @AutoConfigureMetrics.

Mocking and Spying Beans

When running tests, it is sometimes necessary to mock certain components within your application context. For example, you may have a facade over some remote service that is unavailable during development. Mocking can also be useful when you want to simulate failures that might be hard to trigger in a real environment.

Spring Boot includes a @MockBean annotation that can be used to define a Mockito mock for a bean inside your ApplicationContext. You can use the annotation to add new beans or replace a single existing bean definition. The annotation can be used directly on test classes, on fields within your test, or on @Configuration classes and fields. When used on a field, the instance of the created mock is also injected. Mock beans are automatically reset after each test method.

If your test uses one of Spring Boot’s test annotations (such as @SpringBootTest), this feature is automatically enabled. To use this feature with a different arrangement, listeners must be explicitly added, as shown in the following example:

Java
import org.springframework.boot.test.mock.mockito.MockitoTestExecutionListener;
import org.springframework.boot.test.mock.mockito.ResetMocksTestExecutionListener;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.TestExecutionListeners;

@ContextConfiguration(classes = MyConfig.class)
@TestExecutionListeners({ MockitoTestExecutionListener.class, ResetMocksTestExecutionListener.class })
class MyTests {

    // ...

}
Kotlin
import org.springframework.boot.test.mock.mockito.MockitoTestExecutionListener
import org.springframework.boot.test.mock.mockito.ResetMocksTestExecutionListener
import org.springframework.test.context.ContextConfiguration
import org.springframework.test.context.TestExecutionListeners

@ContextConfiguration(classes = [MyConfig::class])
@TestExecutionListeners(
    MockitoTestExecutionListener::class,
    ResetMocksTestExecutionListener::class
)
class MyTests {

    // ...

}

The following example replaces an existing RemoteService bean with a mock implementation:

Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.mock.mockito.MockBean;

import static org.assertj.core.api.Assertions.assertThat;
import static org.mockito.BDDMockito.given;

@SpringBootTest
class MyTests {

    @Autowired
    private Reverser reverser;

    @MockBean
    private RemoteService remoteService;

    @Test
    void exampleTest() {
        given(this.remoteService.getValue()).willReturn("spring");
        String reverse = this.reverser.getReverseValue(); // Calls injected RemoteService
        assertThat(reverse).isEqualTo("gnirps");
    }

}
Kotlin
import org.assertj.core.api.Assertions.assertThat
import org.junit.jupiter.api.Test
import org.mockito.BDDMockito.given
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.boot.test.mock.mockito.MockBean

@SpringBootTest
class MyTests(@Autowired val reverser: Reverser, @MockBean val remoteService: RemoteService) {

    @Test
    fun exampleTest() {
        given(remoteService.value).willReturn("spring")
        val reverse = reverser.reverseValue // Calls injected RemoteService
        assertThat(reverse).isEqualTo("gnirps")
    }

}
@MockBean cannot be used to mock the behavior of a bean that is exercised during application context refresh. By the time the test is executed, the application context refresh has completed and it is too late to configure the mocked behavior. We recommend using a @Bean method to create and configure the mock in this situation.

Additionally, you can use @SpyBean to wrap any existing bean with a Mockito spy. See the Javadoc for full details.

CGLib proxies, such as those created for scoped beans, declare the proxied methods as final. This stops Mockito from functioning correctly as it cannot mock or spy on final methods in its default configuration. If you want to mock or spy on such a bean, configure Mockito to use its inline mock maker by adding org.mockito:mockito-inline to your application’s test dependencies. This allows Mockito to mock and spy on final methods.
While Spring’s test framework caches application contexts between tests and reuses a context for tests sharing the same configuration, the use of @MockBean or @SpyBean influences the cache key, which will most likely increase the number of contexts.
If you are using @SpyBean to spy on a bean with @Cacheable methods that refer to parameters by name, your application must be compiled with -parameters. This ensures that the parameter names are available to the caching infrastructure once the bean has been spied upon.
When you are using @SpyBean to spy on a bean that is proxied by Spring, you may need to remove Spring’s proxy in some situations, for example when setting expectations using given or when. Use AopTestUtils.getTargetObject(yourProxiedSpy) to do so.
Auto-configured Tests

Spring Boot’s auto-configuration system works well for applications but can sometimes be a little too much for tests. It often helps to load only the parts of the configuration that are required to test a “slice” of your application. For example, you might want to test that Spring MVC controllers are mapping URLs correctly, and you do not want to involve database calls in those tests, or you might want to test JPA entities, and you are not interested in the web layer when those tests run.

The spring-boot-test-autoconfigure module includes a number of annotations that can be used to automatically configure such “slices”. Each of them works in a similar way, providing a @…​Test annotation that loads the ApplicationContext and one or more @AutoConfigure…​ annotations that can be used to customize auto-configuration settings.

Each slice restricts component scan to appropriate components and loads a very restricted set of auto-configuration classes. If you need to exclude one of them, most @…​Test annotations provide an excludeAutoConfiguration attribute. Alternatively, you can use @ImportAutoConfiguration#exclude.
Including multiple “slices” by using several @…​Test annotations in one test is not supported. If you need multiple “slices”, pick one of the @…​Test annotations and include the @AutoConfigure…​ annotations of the other “slices” by hand.
It is also possible to use the @AutoConfigure…​ annotations with the standard @SpringBootTest annotation. You can use this combination if you are not interested in “slicing” your application but you want some of the auto-configured test beans.
Auto-configured JSON Tests

To test that object JSON serialization and deserialization is working as expected, you can use the @JsonTest annotation. @JsonTest auto-configures the available supported JSON mapper, which can be one of the following libraries:

  • Jackson ObjectMapper, any @JsonComponent beans and any Jackson Modules

  • Gson

  • Jsonb

A list of the auto-configurations that are enabled by @JsonTest can be found in the appendix.

If you need to configure elements of the auto-configuration, you can use the @AutoConfigureJsonTesters annotation.

Spring Boot includes AssertJ-based helpers that work with the JSONAssert and JsonPath libraries to check that JSON appears as expected. The JacksonTester, GsonTester, JsonbTester, and BasicJsonTester classes can be used for Jackson, Gson, Jsonb, and Strings respectively. Any helper fields on the test class can be @Autowired when using @JsonTest. The following example shows a test class for Jackson:

Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.json.JsonTest;
import org.springframework.boot.test.json.JacksonTester;

import static org.assertj.core.api.Assertions.assertThat;

@JsonTest
class MyJsonTests {

    @Autowired
    private JacksonTester<VehicleDetails> json;

    @Test
    void serialize() throws Exception {
        VehicleDetails details = new VehicleDetails("Honda", "Civic");
        // Assert against a `.json` file in the same package as the test
        assertThat(this.json.write(details)).isEqualToJson("expected.json");
        // Or use JSON path based assertions
        assertThat(this.json.write(details)).hasJsonPathStringValue("@.make");
        assertThat(this.json.write(details)).extractingJsonPathStringValue("@.make").isEqualTo("Honda");
    }

    @Test
    void deserialize() throws Exception {
        String content = "{\"make\":\"Ford\",\"model\":\"Focus\"}";
        assertThat(this.json.parse(content)).isEqualTo(new VehicleDetails("Ford", "Focus"));
        assertThat(this.json.parseObject(content).getMake()).isEqualTo("Ford");
    }

}
Kotlin
import org.assertj.core.api.Assertions.assertThat
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.json.JsonTest
import org.springframework.boot.test.json.JacksonTester

@JsonTest
class MyJsonTests(@Autowired val json: JacksonTester<VehicleDetails>) {

    @Test
    fun serialize() {
        val details = VehicleDetails("Honda", "Civic")
        // Assert against a `.json` file in the same package as the test
        assertThat(json.write(details)).isEqualToJson("expected.json")
        // Or use JSON path based assertions
        assertThat(json.write(details)).hasJsonPathStringValue("@.make")
        assertThat(json.write(details)).extractingJsonPathStringValue("@.make").isEqualTo("Honda")
    }

    @Test
    fun deserialize() {
        val content = "{\"make\":\"Ford\",\"model\":\"Focus\"}"
        assertThat(json.parse(content)).isEqualTo(VehicleDetails("Ford", "Focus"))
        assertThat(json.parseObject(content).make).isEqualTo("Ford")
    }

}
JSON helper classes can also be used directly in standard unit tests. To do so, call the initFields method of the helper in your @Before method if you do not use @JsonTest.

If you use Spring Boot’s AssertJ-based helpers to assert on a number value at a given JSON path, you might not be able to use isEqualTo depending on the type. Instead, you can use AssertJ’s satisfies to assert that the value matches the given condition. For instance, the following example asserts that the actual number is a float value close to 0.15 within an offset of 0.01.

Java
@Test
void someTest() throws Exception {
    SomeObject value = new SomeObject(0.152f);
    assertThat(this.json.write(value)).extractingJsonPathNumberValue("@.test.numberValue")
        .satisfies((number) -> assertThat(number.floatValue()).isCloseTo(0.15f, within(0.01f)));
}
Kotlin
@Test
fun someTest() {
    val value = SomeObject(0.152f)
    assertThat(json.write(value)).extractingJsonPathNumberValue("@.test.numberValue")
        .satisfies(ThrowingConsumer { number ->
            assertThat(number.toFloat()).isCloseTo(0.15f, within(0.01f))
        })
}
Auto-configured Spring MVC Tests

To test whether Spring MVC controllers are working as expected, use the @WebMvcTest annotation. @WebMvcTest auto-configures the Spring MVC infrastructure and limits scanned beans to @Controller, @ControllerAdvice, @JsonComponent, Converter, GenericConverter, Filter, HandlerInterceptor, WebMvcConfigurer, WebMvcRegistrations, and HandlerMethodArgumentResolver. Regular @Component and @ConfigurationProperties beans are not scanned when the @WebMvcTest annotation is used. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans.

A list of the auto-configuration settings that are enabled by @WebMvcTest can be found in the appendix.
If you need to register extra components, such as the Jackson Module, you can import additional configuration classes by using @Import on your test.

Often, @WebMvcTest is limited to a single controller and is used in combination with @MockBean to provide mock implementations for required collaborators.

@WebMvcTest also auto-configures MockMvc. Mock MVC offers a powerful way to quickly test MVC controllers without needing to start a full HTTP server.

You can also auto-configure MockMvc in a non-@WebMvcTest (such as @SpringBootTest) by annotating it with @AutoConfigureMockMvc. The following example uses MockMvc:
Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import org.springframework.boot.test.mock.mockito.MockBean;
import org.springframework.http.MediaType;
import org.springframework.test.web.servlet.MockMvc;

import static org.mockito.BDDMockito.given;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

@WebMvcTest(UserVehicleController.class)
class MyControllerTests {

    @Autowired
    private MockMvc mvc;

    @MockBean
    private UserVehicleService userVehicleService;

    @Test
    void testExample() throws Exception {
        given(this.userVehicleService.getVehicleDetails("sboot"))
            .willReturn(new VehicleDetails("Honda", "Civic"));
        this.mvc.perform(get("/sboot/vehicle").accept(MediaType.TEXT_PLAIN))
            .andExpect(status().isOk())
            .andExpect(content().string("Honda Civic"));
    }

}
Kotlin
import org.junit.jupiter.api.Test
import org.mockito.BDDMockito.given
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest
import org.springframework.boot.test.mock.mockito.MockBean
import org.springframework.http.MediaType
import org.springframework.test.web.servlet.MockMvc
import org.springframework.test.web.servlet.request.MockMvcRequestBuilders
import org.springframework.test.web.servlet.result.MockMvcResultMatchers

@WebMvcTest(UserVehicleController::class)
class MyControllerTests(@Autowired val mvc: MockMvc) {

    @MockBean
    lateinit var userVehicleService: UserVehicleService

    @Test
    fun testExample() {
        given(userVehicleService.getVehicleDetails("sboot"))
            .willReturn(VehicleDetails("Honda", "Civic"))
        mvc.perform(MockMvcRequestBuilders.get("/sboot/vehicle").accept(MediaType.TEXT_PLAIN))
            .andExpect(MockMvcResultMatchers.status().isOk)
            .andExpect(MockMvcResultMatchers.content().string("Honda Civic"))
    }

}
If you need to configure elements of the auto-configuration (for example, when servlet filters should be applied) you can use attributes in the @AutoConfigureMockMvc annotation.

If you use HtmlUnit and Selenium, auto-configuration also provides an HtmlUnit WebClient bean and/or a Selenium WebDriver bean. The following example uses HtmlUnit:

Java
import com.gargoylesoftware.htmlunit.WebClient;
import com.gargoylesoftware.htmlunit.html.HtmlPage;
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import org.springframework.boot.test.mock.mockito.MockBean;

import static org.assertj.core.api.Assertions.assertThat;
import static org.mockito.BDDMockito.given;

@WebMvcTest(UserVehicleController.class)
class MyHtmlUnitTests {

    @Autowired
    private WebClient webClient;

    @MockBean
    private UserVehicleService userVehicleService;

    @Test
    void testExample() throws Exception {
        given(this.userVehicleService.getVehicleDetails("sboot")).willReturn(new VehicleDetails("Honda", "Civic"));
        HtmlPage page = this.webClient.getPage("/sboot/vehicle.html");
        assertThat(page.getBody().getTextContent()).isEqualTo("Honda Civic");
    }

}
Kotlin
import com.gargoylesoftware.htmlunit.WebClient
import com.gargoylesoftware.htmlunit.html.HtmlPage
import org.assertj.core.api.Assertions.assertThat
import org.junit.jupiter.api.Test
import org.mockito.BDDMockito.given
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest
import org.springframework.boot.test.mock.mockito.MockBean

@WebMvcTest(UserVehicleController::class)
class MyHtmlUnitTests(@Autowired val webClient: WebClient) {

    @MockBean
    lateinit var userVehicleService: UserVehicleService

    @Test
    fun testExample() {
        given(userVehicleService.getVehicleDetails("sboot")).willReturn(VehicleDetails("Honda", "Civic"))
        val page = webClient.getPage<HtmlPage>("/sboot/vehicle.html")
        assertThat(page.body.textContent).isEqualTo("Honda Civic")
    }

}
By default, Spring Boot puts WebDriver beans in a special “scope” to ensure that the driver exits after each test and that a new instance is injected. If you do not want this behavior, you can add @Scope("singleton") to your WebDriver @Bean definition.
The webDriver scope created by Spring Boot will replace any user defined scope of the same name. If you define your own webDriver scope you may find it stops working when you use @WebMvcTest.

If you have Spring Security on the classpath, @WebMvcTest will also scan WebSecurityConfigurer beans. Instead of disabling security completely for such tests, you can use Spring Security’s test support. More details on how to use Spring Security’s MockMvc support can be found in this Testing With Spring Security how-to section.

Sometimes writing Spring MVC tests is not enough; Spring Boot can help you run full end-to-end tests with an actual server.
Auto-configured Spring WebFlux Tests

To test that Spring WebFlux controllers are working as expected, you can use the @WebFluxTest annotation. @WebFluxTest auto-configures the Spring WebFlux infrastructure and limits scanned beans to @Controller, @ControllerAdvice, @JsonComponent, Converter, GenericConverter, WebFilter, and WebFluxConfigurer. Regular @Component and @ConfigurationProperties beans are not scanned when the @WebFluxTest annotation is used. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans.

A list of the auto-configurations that are enabled by @WebFluxTest can be found in the appendix.
If you need to register extra components, such as Jackson Module, you can import additional configuration classes using @Import on your test.

Often, @WebFluxTest is limited to a single controller and used in combination with the @MockBean annotation to provide mock implementations for required collaborators.

@WebFluxTest also auto-configures WebTestClient, which offers a powerful way to quickly test WebFlux controllers without needing to start a full HTTP server.

You can also auto-configure WebTestClient in a non-@WebFluxTest (such as @SpringBootTest) by annotating it with @AutoConfigureWebTestClient. The following example shows a class that uses both @WebFluxTest and a WebTestClient:
Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest;
import org.springframework.boot.test.mock.mockito.MockBean;
import org.springframework.http.MediaType;
import org.springframework.test.web.reactive.server.WebTestClient;

import static org.mockito.BDDMockito.given;

@WebFluxTest(UserVehicleController.class)
class MyControllerTests {

    @Autowired
    private WebTestClient webClient;

    @MockBean
    private UserVehicleService userVehicleService;

    @Test
    void testExample() {
        given(this.userVehicleService.getVehicleDetails("sboot"))
            .willReturn(new VehicleDetails("Honda", "Civic"));
        this.webClient.get().uri("/sboot/vehicle").accept(MediaType.TEXT_PLAIN).exchange()
            .expectStatus().isOk()
            .expectBody(String.class).isEqualTo("Honda Civic");
    }

}
Kotlin
import org.junit.jupiter.api.Test
import org.mockito.BDDMockito.given
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest
import org.springframework.boot.test.mock.mockito.MockBean
import org.springframework.http.MediaType
import org.springframework.test.web.reactive.server.WebTestClient
import org.springframework.test.web.reactive.server.expectBody

@WebFluxTest(UserVehicleController::class)
class MyControllerTests(@Autowired val webClient: WebTestClient) {

    @MockBean
    lateinit var userVehicleService: UserVehicleService

    @Test
    fun testExample() {
        given(userVehicleService.getVehicleDetails("sboot"))
            .willReturn(VehicleDetails("Honda", "Civic"))
        webClient.get().uri("/sboot/vehicle").accept(MediaType.TEXT_PLAIN).exchange()
            .expectStatus().isOk
            .expectBody<String>().isEqualTo("Honda Civic")
    }

}
This setup is only supported by WebFlux applications as using WebTestClient in a mocked web application only works with WebFlux at the moment.
@WebFluxTest cannot detect routes registered through the functional web framework. For testing RouterFunction beans in the context, consider importing your RouterFunction yourself by using @Import or by using @SpringBootTest.
@WebFluxTest cannot detect custom security configuration registered as a @Bean of type SecurityWebFilterChain. To include that in your test, you will need to import the configuration that registers the bean by using @Import or by using @SpringBootTest.
Sometimes writing Spring WebFlux tests is not enough; Spring Boot can help you run full end-to-end tests with an actual server.
Auto-configured Spring GraphQL Tests

Spring GraphQL offers a dedicated testing support module; you’ll need to add it to your project:

Maven
<dependencies>
    <dependency>
        <groupId>org.springframework.graphql</groupId>
        <artifactId>spring-graphql-test</artifactId>
        <scope>test</scope>
    </dependency>
    <!-- Unless already present in the compile scope -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-webflux</artifactId>
        <scope>test</scope>
    </dependency>
</dependencies>
Gradle
dependencies {
    testImplementation("org.springframework.graphql:spring-graphql-test")
    // Unless already present in the implementation configuration
    testImplementation("org.springframework.boot:spring-boot-starter-webflux")
}

This testing module ships the GraphQlTester. The tester is heavily used in test, so be sure to become familiar with using it. There are GraphQlTester variants and Spring Boot will auto-configure them depending on the type of tests:

  • the ExecutionGraphQlServiceTester performs tests on the server side, without a client nor a transport

  • the HttpGraphQlTester performs tests with a client that connects to a server, with or without a live server

Spring Boot helps you to test your Spring GraphQL Controllers with the @GraphQlTest annotation. @GraphQlTest auto-configures the Spring GraphQL infrastructure, without any transport nor server being involved. This limits scanned beans to @Controller, RuntimeWiringConfigurer, JsonComponent, Converter, GenericConverter, DataFetcherExceptionResolver, Instrumentation and GraphQlSourceBuilderCustomizer. Regular @Component and @ConfigurationProperties beans are not scanned when the @GraphQlTest annotation is used. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans.

A list of the auto-configurations that are enabled by @GraphQlTest can be found in the appendix.
If you need to register extra components, such as Jackson Module, you can import additional configuration classes using @Import on your test.

Often, @GraphQlTest is limited to a set of controllers and used in combination with the @MockBean annotation to provide mock implementations for required collaborators.

Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.docs.web.graphql.runtimewiring.GreetingController;
import org.springframework.boot.test.autoconfigure.graphql.GraphQlTest;
import org.springframework.graphql.test.tester.GraphQlTester;

@GraphQlTest(GreetingController.class)
class GreetingControllerTests {

    @Autowired
    private GraphQlTester graphQlTester;

    @Test
    void shouldGreetWithSpecificName() {
        this.graphQlTester.document("{ greeting(name: \"Alice\") } ")
            .execute()
            .path("greeting")
            .entity(String.class)
            .isEqualTo("Hello, Alice!");
    }

    @Test
    void shouldGreetWithDefaultName() {
        this.graphQlTester.document("{ greeting } ")
            .execute()
            .path("greeting")
            .entity(String.class)
            .isEqualTo("Hello, Spring!");
    }

}
Kotlin
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.docs.web.graphql.runtimewiring.GreetingController
import org.springframework.boot.test.autoconfigure.graphql.GraphQlTest
import org.springframework.graphql.test.tester.GraphQlTester

@GraphQlTest(GreetingController::class)
internal class GreetingControllerTests {

    @Autowired
    lateinit var graphQlTester: GraphQlTester

    @Test
    fun shouldGreetWithSpecificName() {
        graphQlTester.document("{ greeting(name: \"Alice\") } ").execute().path("greeting").entity(String::class.java)
                .isEqualTo("Hello, Alice!")
    }

    @Test
    fun shouldGreetWithDefaultName() {
        graphQlTester.document("{ greeting } ").execute().path("greeting").entity(String::class.java)
                .isEqualTo("Hello, Spring!")
    }

}

@SpringBootTest tests are full integration tests and involve the entire application. When using a random or defined port, a live server is configured and an HttpGraphQlTester bean is contributed automatically so you can use it to test your server. When a MOCK environment is configured, you can also request an HttpGraphQlTester bean by annotating your test class with @AutoConfigureHttpGraphQlTester:

Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.graphql.tester.AutoConfigureHttpGraphQlTester;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.graphql.test.tester.HttpGraphQlTester;

@AutoConfigureHttpGraphQlTester
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.MOCK)
class GraphQlIntegrationTests {

    @Test
    void shouldGreetWithSpecificName(@Autowired HttpGraphQlTester graphQlTester) {
        HttpGraphQlTester authenticatedTester = graphQlTester.mutate()
            .webTestClient((client) -> client.defaultHeaders((headers) -> headers.setBasicAuth("admin", "ilovespring")))
            .build();
        authenticatedTester.document("{ greeting(name: \"Alice\") } ")
            .execute()
            .path("greeting")
            .entity(String.class)
            .isEqualTo("Hello, Alice!");
    }

}
Kotlin
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.graphql.tester.AutoConfigureHttpGraphQlTester
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.graphql.test.tester.HttpGraphQlTester
import org.springframework.http.HttpHeaders
import org.springframework.test.web.reactive.server.WebTestClient

@AutoConfigureHttpGraphQlTester
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.MOCK)
class GraphQlIntegrationTests {

    @Test
    fun shouldGreetWithSpecificName(@Autowired graphQlTester: HttpGraphQlTester) {
        val authenticatedTester = graphQlTester.mutate()
            .webTestClient { client: WebTestClient.Builder ->
                client.defaultHeaders { headers: HttpHeaders ->
                    headers.setBasicAuth("admin", "ilovespring")
                }
            }.build()
        authenticatedTester.document("{ greeting(name: \"Alice\") } ").execute()
            .path("greeting").entity(String::class.java).isEqualTo("Hello, Alice!")
    }
}
Auto-configured Data Cassandra Tests

You can use @DataCassandraTest to test Cassandra applications. By default, it configures a CassandraTemplate, scans for @Table classes, and configures Spring Data Cassandra repositories. Regular @Component and @ConfigurationProperties beans are not scanned when the @DataCassandraTest annotation is used. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans. (For more about using Cassandra with Spring Boot, see "Cassandra".)

A list of the auto-configuration settings that are enabled by @DataCassandraTest can be found in the appendix.

The following example shows a typical setup for using Cassandra tests in Spring Boot:

Java
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.cassandra.DataCassandraTest;

@DataCassandraTest
class MyDataCassandraTests {

    @Autowired
    private SomeRepository repository;

}
Kotlin
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.data.cassandra.DataCassandraTest

@DataCassandraTest
class MyDataCassandraTests(@Autowired val repository: SomeRepository)
Auto-configured Data Couchbase Tests

You can use @DataCouchbaseTest to test Couchbase applications. By default, it configures a CouchbaseTemplate or ReactiveCouchbaseTemplate, scans for @Document classes, and configures Spring Data Couchbase repositories. Regular @Component and @ConfigurationProperties beans are not scanned when the @DataCouchbaseTest annotation is used. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans. (For more about using Couchbase with Spring Boot, see "Couchbase", earlier in this chapter.)

A list of the auto-configuration settings that are enabled by @DataCouchbaseTest can be found in the appendix.

The following example shows a typical setup for using Couchbase tests in Spring Boot:

Java
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.couchbase.DataCouchbaseTest;

@DataCouchbaseTest
class MyDataCouchbaseTests {

    @Autowired
    private SomeRepository repository;

    // ...

}
Kotlin
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.data.couchbase.DataCouchbaseTest

@DataCouchbaseTest
class MyDataCouchbaseTests(@Autowired val repository: SomeRepository) {

    // ...

}
Auto-configured Data Elasticsearch Tests

You can use @DataElasticsearchTest to test Elasticsearch applications. By default, it configures an ElasticsearchRestTemplate, scans for @Document classes, and configures Spring Data Elasticsearch repositories. Regular @Component and @ConfigurationProperties beans are not scanned when the @DataElasticsearchTest annotation is used. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans. (For more about using Elasticsearch with Spring Boot, see "Elasticsearch", earlier in this chapter.)

A list of the auto-configuration settings that are enabled by @DataElasticsearchTest can be found in the appendix.

The following example shows a typical setup for using Elasticsearch tests in Spring Boot:

Java
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.elasticsearch.DataElasticsearchTest;

@DataElasticsearchTest
class MyDataElasticsearchTests {

    @Autowired
    private SomeRepository repository;

    // ...

}
Kotlin
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.data.elasticsearch.DataElasticsearchTest

@DataElasticsearchTest
class MyDataElasticsearchTests(@Autowired val repository: SomeRepository) {

    // ...

}
Auto-configured Data JPA Tests

You can use the @DataJpaTest annotation to test JPA applications. By default, it scans for @Entity classes and configures Spring Data JPA repositories. If an embedded database is available on the classpath, it configures one as well. SQL queries are logged by default by setting the spring.jpa.show-sql property to true. This can be disabled using the showSql() attribute of the annotation.

Regular @Component and @ConfigurationProperties beans are not scanned when the @DataJpaTest annotation is used. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans.

A list of the auto-configuration settings that are enabled by @DataJpaTest can be found in the appendix.

By default, data JPA tests are transactional and roll back at the end of each test. See the relevant section in the Spring Framework Reference Documentation for more details. If that is not what you want, you can disable transaction management for a test or for the whole class as follows:

Java
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;

@DataJpaTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyNonTransactionalTests {

    // ...

}
Kotlin
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest
import org.springframework.transaction.annotation.Propagation
import org.springframework.transaction.annotation.Transactional

@DataJpaTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyNonTransactionalTests {

    // ...

}

Data JPA tests may also inject a TestEntityManager bean, which provides an alternative to the standard JPA EntityManager that is specifically designed for tests.

TestEntityManager can also be auto-configured to any of your Spring-based test class by adding @AutoConfigureTestEntityManager. When doing so, make sure that your test is running in a transaction, for instance by adding @Transactional on your test class or method.

A JdbcTemplate is also available if you need that. The following example shows the @DataJpaTest annotation in use:

Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
import org.springframework.boot.test.autoconfigure.orm.jpa.TestEntityManager;

import static org.assertj.core.api.Assertions.assertThat;

@DataJpaTest
class MyRepositoryTests {

    @Autowired
    private TestEntityManager entityManager;

    @Autowired
    private UserRepository repository;

    @Test
    void testExample() {
        this.entityManager.persist(new User("sboot", "1234"));
        User user = this.repository.findByUsername("sboot");
        assertThat(user.getUsername()).isEqualTo("sboot");
        assertThat(user.getEmployeeNumber()).isEqualTo("1234");
    }

}
Kotlin
import org.assertj.core.api.Assertions.assertThat
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest
import org.springframework.boot.test.autoconfigure.orm.jpa.TestEntityManager

@DataJpaTest
class MyRepositoryTests(@Autowired val entityManager: TestEntityManager, @Autowired val repository: UserRepository) {

    @Test
    fun testExample() {
        entityManager.persist(User("sboot", "1234"))
        val user = repository.findByUsername("sboot")
        assertThat(user?.username).isEqualTo("sboot")
        assertThat(user?.employeeNumber).isEqualTo("1234")
    }

}

In-memory embedded databases generally work well for tests, since they are fast and do not require any installation. If, however, you prefer to run tests against a real database you can use the @AutoConfigureTestDatabase annotation, as shown in the following example:

Java
import org.springframework.boot.test.autoconfigure.jdbc.AutoConfigureTestDatabase;
import org.springframework.boot.test.autoconfigure.jdbc.AutoConfigureTestDatabase.Replace;
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;

@DataJpaTest
@AutoConfigureTestDatabase(replace = Replace.NONE)
class MyRepositoryTests {

    // ...

}
Kotlin
import org.springframework.boot.test.autoconfigure.jdbc.AutoConfigureTestDatabase
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest

@DataJpaTest
@AutoConfigureTestDatabase(replace = AutoConfigureTestDatabase.Replace.NONE)
class MyRepositoryTests {

    // ...

}
Auto-configured JDBC Tests

@JdbcTest is similar to @DataJpaTest but is for tests that only require a DataSource and do not use Spring Data JDBC. By default, it configures an in-memory embedded database and a JdbcTemplate. Regular @Component and @ConfigurationProperties beans are not scanned when the @JdbcTest annotation is used. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans.

A list of the auto-configurations that are enabled by @JdbcTest can be found in the appendix.

By default, JDBC tests are transactional and roll back at the end of each test. See the relevant section in the Spring Framework Reference Documentation for more details. If that is not what you want, you can disable transaction management for a test or for the whole class, as follows:

Java
import org.springframework.boot.test.autoconfigure.jdbc.JdbcTest;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;

@JdbcTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyTransactionalTests {

}
Kotlin
import org.springframework.boot.test.autoconfigure.jdbc.JdbcTest
import org.springframework.transaction.annotation.Propagation
import org.springframework.transaction.annotation.Transactional

@JdbcTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyTransactionalTests

If you prefer your test to run against a real database, you can use the @AutoConfigureTestDatabase annotation in the same way as for @DataJpaTest. (See "Auto-configured Data JPA Tests".)

Auto-configured Data JDBC Tests

@DataJdbcTest is similar to @JdbcTest but is for tests that use Spring Data JDBC repositories. By default, it configures an in-memory embedded database, a JdbcTemplate, and Spring Data JDBC repositories. Only AbstractJdbcConfiguration sub-classes are scanned when the @DataJdbcTest annotation is used, regular @Component and @ConfigurationProperties beans are not scanned. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans.

A list of the auto-configurations that are enabled by @DataJdbcTest can be found in the appendix.

By default, Data JDBC tests are transactional and roll back at the end of each test. See the relevant section in the Spring Framework Reference Documentation for more details. If that is not what you want, you can disable transaction management for a test or for the whole test class as shown in the JDBC example.

If you prefer your test to run against a real database, you can use the @AutoConfigureTestDatabase annotation in the same way as for @DataJpaTest. (See "Auto-configured Data JPA Tests".)

Auto-configured Data R2DBC Tests

@DataR2dbcTest is similar to @DataJdbcTest but is for tests that use Spring Data R2DBC repositories. By default, it configures an in-memory embedded database, an R2dbcEntityTemplate, and Spring Data R2DBC repositories. Regular @Component and @ConfigurationProperties beans are not scanned when the @DataR2dbcTest annotation is used. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans.

A list of the auto-configurations that are enabled by @DataR2dbcTest can be found in the appendix.

By default, Data R2DBC tests are not transactional.

If you prefer your test to run against a real database, you can use the @AutoConfigureTestDatabase annotation in the same way as for @DataJpaTest. (See "Auto-configured Data JPA Tests".)

Auto-configured jOOQ Tests

You can use @JooqTest in a similar fashion as @JdbcTest but for jOOQ-related tests. As jOOQ relies heavily on a Java-based schema that corresponds with the database schema, the existing DataSource is used. If you want to replace it with an in-memory database, you can use @AutoConfigureTestDatabase to override those settings. (For more about using jOOQ with Spring Boot, see "Using jOOQ".) Regular @Component and @ConfigurationProperties beans are not scanned when the @JooqTest annotation is used. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans.

A list of the auto-configurations that are enabled by @JooqTest can be found in the appendix.

@JooqTest configures a DSLContext. The following example shows the @JooqTest annotation in use:

Java
import org.jooq.DSLContext;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.jooq.JooqTest;

@JooqTest
class MyJooqTests {

    @Autowired
    private DSLContext dslContext;

    // ...

}
Kotlin
import org.jooq.DSLContext
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.jooq.JooqTest

@JooqTest
class MyJooqTests(@Autowired val dslContext: DSLContext) {

    // ...

}

JOOQ tests are transactional and roll back at the end of each test by default. If that is not what you want, you can disable transaction management for a test or for the whole test class as shown in the JDBC example.

Auto-configured Data MongoDB Tests

You can use @DataMongoTest to test MongoDB applications. By default, it configures an in-memory embedded MongoDB (if available), configures a MongoTemplate, scans for @Document classes, and configures Spring Data MongoDB repositories. Regular @Component and @ConfigurationProperties beans are not scanned when the @DataMongoTest annotation is used. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans. (For more about using MongoDB with Spring Boot, see "MongoDB".)

A list of the auto-configuration settings that are enabled by @DataMongoTest can be found in the appendix.

The following class shows the @DataMongoTest annotation in use:

Java
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest;
import org.springframework.data.mongodb.core.MongoTemplate;

@DataMongoTest
class MyDataMongoDbTests {

    @Autowired
    private MongoTemplate mongoTemplate;

    // ...

}
Kotlin
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest
import org.springframework.data.mongodb.core.MongoTemplate

@DataMongoTest
class MyDataMongoDbTests(@Autowired val mongoTemplate: MongoTemplate) {

    // ...

}

In-memory embedded MongoDB generally works well for tests, since it is fast and does not require any developer installation. If, however, you prefer to run tests against a real MongoDB server, you should exclude the embedded MongoDB auto-configuration, as shown in the following example:

Java
import org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration;
import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest;

@DataMongoTest(excludeAutoConfiguration = EmbeddedMongoAutoConfiguration.class)
class MyDataMongoDbTests {

    // ...

}
Kotlin
import org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration
import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest

@DataMongoTest(excludeAutoConfiguration = [EmbeddedMongoAutoConfiguration::class])
class MyDataMongoDbTests {

    // ...

}
Auto-configured Data Neo4j Tests

You can use @DataNeo4jTest to test Neo4j applications. By default, it scans for @Node classes, and configures Spring Data Neo4j repositories. Regular @Component and @ConfigurationProperties beans are not scanned when the @DataNeo4jTest annotation is used. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans. (For more about using Neo4J with Spring Boot, see "Neo4j".)

A list of the auto-configuration settings that are enabled by @DataNeo4jTest can be found in the appendix.

The following example shows a typical setup for using Neo4J tests in Spring Boot:

Java
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.neo4j.DataNeo4jTest;

@DataNeo4jTest
class MyDataNeo4jTests {

    @Autowired
    private SomeRepository repository;

    // ...

}
Kotlin
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.data.neo4j.DataNeo4jTest

@DataNeo4jTest
class MyDataNeo4jTests(@Autowired val repository: SomeRepository) {

    // ...

}

By default, Data Neo4j tests are transactional and roll back at the end of each test. See the relevant section in the Spring Framework Reference Documentation for more details. If that is not what you want, you can disable transaction management for a test or for the whole class, as follows:

Java
import org.springframework.boot.test.autoconfigure.data.neo4j.DataNeo4jTest;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;

@DataNeo4jTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyDataNeo4jTests {

}
Kotlin
import org.springframework.boot.test.autoconfigure.data.neo4j.DataNeo4jTest
import org.springframework.transaction.annotation.Propagation
import org.springframework.transaction.annotation.Transactional

@DataNeo4jTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyDataNeo4jTests
Transactional tests are not supported with reactive access. If you are using this style, you must configure @DataNeo4jTest tests as described above.
Auto-configured Data Redis Tests

You can use @DataRedisTest to test Redis applications. By default, it scans for @RedisHash classes and configures Spring Data Redis repositories. Regular @Component and @ConfigurationProperties beans are not scanned when the @DataRedisTest annotation is used. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans. (For more about using Redis with Spring Boot, see "Redis".)

A list of the auto-configuration settings that are enabled by @DataRedisTest can be found in the appendix.

The following example shows the @DataRedisTest annotation in use:

Java
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.redis.DataRedisTest;

@DataRedisTest
class MyDataRedisTests {

    @Autowired
    private SomeRepository repository;

    // ...

}
Kotlin
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.data.redis.DataRedisTest

@DataRedisTest
class MyDataRedisTests(@Autowired val repository: SomeRepository) {

    // ...

}
Auto-configured Data LDAP Tests

You can use @DataLdapTest to test LDAP applications. By default, it configures an in-memory embedded LDAP (if available), configures an LdapTemplate, scans for @Entry classes, and configures Spring Data LDAP repositories. Regular @Component and @ConfigurationProperties beans are not scanned when the @DataLdapTest annotation is used. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans. (For more about using LDAP with Spring Boot, see "LDAP".)

A list of the auto-configuration settings that are enabled by @DataLdapTest can be found in the appendix.

The following example shows the @DataLdapTest annotation in use:

Java
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.ldap.DataLdapTest;
import org.springframework.ldap.core.LdapTemplate;

@DataLdapTest
class MyDataLdapTests {

    @Autowired
    private LdapTemplate ldapTemplate;

    // ...

}
Kotlin
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.data.ldap.DataLdapTest
import org.springframework.ldap.core.LdapTemplate

@DataLdapTest
class MyDataLdapTests(@Autowired val ldapTemplate: LdapTemplate) {

    // ...

}

In-memory embedded LDAP generally works well for tests, since it is fast and does not require any developer installation. If, however, you prefer to run tests against a real LDAP server, you should exclude the embedded LDAP auto-configuration, as shown in the following example:

Java
import org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration;
import org.springframework.boot.test.autoconfigure.data.ldap.DataLdapTest;

@DataLdapTest(excludeAutoConfiguration = EmbeddedLdapAutoConfiguration.class)
class MyDataLdapTests {

    // ...

}
Kotlin
import org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration
import org.springframework.boot.test.autoconfigure.data.ldap.DataLdapTest

@DataLdapTest(excludeAutoConfiguration = [EmbeddedLdapAutoConfiguration::class])
class MyDataLdapTests {

    // ...

}
Auto-configured REST Clients

You can use the @RestClientTest annotation to test REST clients. By default, it auto-configures Jackson, GSON, and Jsonb support, configures a RestTemplateBuilder, and adds support for MockRestServiceServer. Regular @Component and @ConfigurationProperties beans are not scanned when the @RestClientTest annotation is used. @EnableConfigurationProperties can be used to include @ConfigurationProperties beans.

A list of the auto-configuration settings that are enabled by @RestClientTest can be found in the appendix.

The specific beans that you want to test should be specified by using the value or components attribute of @RestClientTest, as shown in the following example:

Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.client.RestClientTest;
import org.springframework.http.MediaType;
import org.springframework.test.web.client.MockRestServiceServer;

import static org.assertj.core.api.Assertions.assertThat;
import static org.springframework.test.web.client.match.MockRestRequestMatchers.requestTo;
import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;

@RestClientTest(RemoteVehicleDetailsService.class)
class MyRestClientTests {

    @Autowired
    private RemoteVehicleDetailsService service;

    @Autowired
    private MockRestServiceServer server;

    @Test
    void getVehicleDetailsWhenResultIsSuccessShouldReturnDetails() {
        this.server.expect(requestTo("/greet/details")).andRespond(withSuccess("hello", MediaType.TEXT_PLAIN));
        String greeting = this.service.callRestService();
        assertThat(greeting).isEqualTo("hello");
    }

}
Kotlin
import org.assertj.core.api.Assertions.assertThat
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.web.client.RestClientTest
import org.springframework.http.MediaType
import org.springframework.test.web.client.MockRestServiceServer
import org.springframework.test.web.client.match.MockRestRequestMatchers
import org.springframework.test.web.client.response.MockRestResponseCreators

@RestClientTest(RemoteVehicleDetailsService::class)
class MyRestClientTests(
    @Autowired val service: RemoteVehicleDetailsService,
    @Autowired val server: MockRestServiceServer) {

    @Test
    fun getVehicleDetailsWhenResultIsSuccessShouldReturnDetails(): Unit {
        server.expect(MockRestRequestMatchers.requestTo("/greet/details"))
            .andRespond(MockRestResponseCreators.withSuccess("hello", MediaType.TEXT_PLAIN))
        val greeting = service.callRestService()
        assertThat(greeting).isEqualTo("hello")
    }

}
Auto-configured Spring REST Docs Tests

You can use the @AutoConfigureRestDocs annotation to use Spring REST Docs in your tests with Mock MVC, REST Assured, or WebTestClient. It removes the need for the JUnit extension in Spring REST Docs.

@AutoConfigureRestDocs can be used to override the default output directory (target/generated-snippets if you are using Maven or build/generated-snippets if you are using Gradle). It can also be used to configure the host, scheme, and port that appears in any documented URIs.

Auto-configured Spring REST Docs Tests With Mock MVC

@AutoConfigureRestDocs customizes the MockMvc bean to use Spring REST Docs when testing servlet-based web applications. You can inject it by using @Autowired and use it in your tests as you normally would when using Mock MVC and Spring REST Docs, as shown in the following example:

Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.restdocs.AutoConfigureRestDocs;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import org.springframework.http.MediaType;
import org.springframework.test.web.servlet.MockMvc;

import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.document;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

@WebMvcTest(UserController.class)
@AutoConfigureRestDocs
class MyUserDocumentationTests {

    @Autowired
    private MockMvc mvc;

    @Test
    void listUsers() throws Exception {
        this.mvc.perform(get("/users").accept(MediaType.TEXT_PLAIN))
            .andExpect(status().isOk())
            .andDo(document("list-users"));
    }

}
Kotlin
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.restdocs.AutoConfigureRestDocs
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest
import org.springframework.http.MediaType
import org.springframework.restdocs.mockmvc.MockMvcRestDocumentation
import org.springframework.test.web.servlet.MockMvc
import org.springframework.test.web.servlet.request.MockMvcRequestBuilders
import org.springframework.test.web.servlet.result.MockMvcResultMatchers

@WebMvcTest(UserController::class)
@AutoConfigureRestDocs
class MyUserDocumentationTests(@Autowired val mvc: MockMvc) {

    @Test
    fun listUsers() {
        mvc.perform(MockMvcRequestBuilders.get("/users").accept(MediaType.TEXT_PLAIN))
            .andExpect(MockMvcResultMatchers.status().isOk)
            .andDo(MockMvcRestDocumentation.document("list-users"))
    }

}

If you require more control over Spring REST Docs configuration than offered by the attributes of @AutoConfigureRestDocs, you can use a RestDocsMockMvcConfigurationCustomizer bean, as shown in the following example:

Java
import org.springframework.boot.test.autoconfigure.restdocs.RestDocsMockMvcConfigurationCustomizer;
import org.springframework.boot.test.context.TestConfiguration;
import org.springframework.restdocs.mockmvc.MockMvcRestDocumentationConfigurer;
import org.springframework.restdocs.templates.TemplateFormats;

@TestConfiguration(proxyBeanMethods = false)
public class MyRestDocsConfiguration implements RestDocsMockMvcConfigurationCustomizer {

    @Override
    public void customize(MockMvcRestDocumentationConfigurer configurer) {
        configurer.snippets().withTemplateFormat(TemplateFormats.markdown());
    }

}
Kotlin
import org.springframework.boot.test.autoconfigure.restdocs.RestDocsMockMvcConfigurationCustomizer
import org.springframework.boot.test.context.TestConfiguration
import org.springframework.restdocs.mockmvc.MockMvcRestDocumentationConfigurer
import org.springframework.restdocs.templates.TemplateFormats

@TestConfiguration(proxyBeanMethods = false)
class MyRestDocsConfiguration : RestDocsMockMvcConfigurationCustomizer {

    override fun customize(configurer: MockMvcRestDocumentationConfigurer) {
        configurer.snippets().withTemplateFormat(TemplateFormats.markdown())
    }

}

If you want to make use of Spring REST Docs support for a parameterized output directory, you can create a RestDocumentationResultHandler bean. The auto-configuration calls alwaysDo with this result handler, thereby causing each MockMvc call to automatically generate the default snippets. The following example shows a RestDocumentationResultHandler being defined:

Java
import org.springframework.boot.test.context.TestConfiguration;
import org.springframework.context.annotation.Bean;
import org.springframework.restdocs.mockmvc.MockMvcRestDocumentation;
import org.springframework.restdocs.mockmvc.RestDocumentationResultHandler;

@TestConfiguration(proxyBeanMethods = false)
public class MyResultHandlerConfiguration {

    @Bean
    public RestDocumentationResultHandler restDocumentation() {
        return MockMvcRestDocumentation.document("{method-name}");
    }

}
Kotlin
import org.springframework.boot.test.context.TestConfiguration
import org.springframework.context.annotation.Bean
import org.springframework.restdocs.mockmvc.MockMvcRestDocumentation
import org.springframework.restdocs.mockmvc.RestDocumentationResultHandler

@TestConfiguration(proxyBeanMethods = false)
class MyResultHandlerConfiguration {

    @Bean
    fun restDocumentation(): RestDocumentationResultHandler {
        return MockMvcRestDocumentation.document("{method-name}")
    }

}
Auto-configured Spring REST Docs Tests With WebTestClient

@AutoConfigureRestDocs can also be used with WebTestClient when testing reactive web applications. You can inject it by using @Autowired and use it in your tests as you normally would when using @WebFluxTest and Spring REST Docs, as shown in the following example:

Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.restdocs.AutoConfigureRestDocs;
import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest;
import org.springframework.test.web.reactive.server.WebTestClient;

import static org.springframework.restdocs.webtestclient.WebTestClientRestDocumentation.document;

@WebFluxTest
@AutoConfigureRestDocs
class MyUsersDocumentationTests {

    @Autowired
    private WebTestClient webTestClient;

    @Test
    void listUsers() {
        this.webTestClient
            .get().uri("/")
        .exchange()
        .expectStatus()
            .isOk()
        .expectBody()
            .consumeWith(document("list-users"));
    }

}
Kotlin
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.restdocs.AutoConfigureRestDocs
import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest
import org.springframework.restdocs.webtestclient.WebTestClientRestDocumentation
import org.springframework.test.web.reactive.server.WebTestClient

@WebFluxTest
@AutoConfigureRestDocs
class MyUsersDocumentationTests(@Autowired val webTestClient: WebTestClient) {

    @Test
    fun listUsers() {
        webTestClient
            .get().uri("/")
            .exchange()
            .expectStatus()
            .isOk
            .expectBody()
            .consumeWith(WebTestClientRestDocumentation.document("list-users"))
    }

}

If you require more control over Spring REST Docs configuration than offered by the attributes of @AutoConfigureRestDocs, you can use a RestDocsWebTestClientConfigurationCustomizer bean, as shown in the following example:

Java
import org.springframework.boot.test.autoconfigure.restdocs.RestDocsWebTestClientConfigurationCustomizer;
import org.springframework.boot.test.context.TestConfiguration;
import org.springframework.restdocs.webtestclient.WebTestClientRestDocumentationConfigurer;

@TestConfiguration(proxyBeanMethods = false)
public class MyRestDocsConfiguration implements RestDocsWebTestClientConfigurationCustomizer {

    @Override
    public void customize(WebTestClientRestDocumentationConfigurer configurer) {
        configurer.snippets().withEncoding("UTF-8");
    }

}
Kotlin
import org.springframework.boot.test.autoconfigure.restdocs.RestDocsWebTestClientConfigurationCustomizer
import org.springframework.boot.test.context.TestConfiguration
import org.springframework.restdocs.webtestclient.WebTestClientRestDocumentationConfigurer

@TestConfiguration(proxyBeanMethods = false)
class MyRestDocsConfiguration : RestDocsWebTestClientConfigurationCustomizer {

    override fun customize(configurer: WebTestClientRestDocumentationConfigurer) {
        configurer.snippets().withEncoding("UTF-8")
    }

}

If you want to make use of Spring REST Docs support for a parameterized output directory, you can use a WebTestClientBuilderCustomizer to configure a consumer for every entity exchange result. The following example shows such a WebTestClientBuilderCustomizer being defined:

Java
import org.springframework.boot.test.context.TestConfiguration;
import org.springframework.boot.test.web.reactive.server.WebTestClientBuilderCustomizer;
import org.springframework.context.annotation.Bean;

import static org.springframework.restdocs.webtestclient.WebTestClientRestDocumentation.document;

@TestConfiguration(proxyBeanMethods = false)
public class MyWebTestClientBuilderCustomizerConfiguration {

    @Bean
    public WebTestClientBuilderCustomizer restDocumentation() {
        return (builder) -> builder.entityExchangeResultConsumer(document("{method-name}"));
    }

}
Kotlin
import org.springframework.boot.test.context.TestConfiguration
import org.springframework.boot.test.web.reactive.server.WebTestClientBuilderCustomizer
import org.springframework.context.annotation.Bean
import org.springframework.restdocs.webtestclient.WebTestClientRestDocumentation
import org.springframework.test.web.reactive.server.WebTestClient

@TestConfiguration(proxyBeanMethods = false)
class MyWebTestClientBuilderCustomizerConfiguration {

    @Bean
    fun restDocumentation(): WebTestClientBuilderCustomizer {
        return WebTestClientBuilderCustomizer { builder: WebTestClient.Builder ->
            builder.entityExchangeResultConsumer(
                WebTestClientRestDocumentation.document("{method-name}")
            )
        }
    }

}
Auto-configured Spring REST Docs Tests With REST Assured

@AutoConfigureRestDocs makes a RequestSpecification bean, preconfigured to use Spring REST Docs, available to your tests. You can inject it by using @Autowired and use it in your tests as you normally would when using REST Assured and Spring REST Docs, as shown in the following example:

Java
import io.restassured.specification.RequestSpecification;
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.restdocs.AutoConfigureRestDocs;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.boot.test.web.server.LocalServerPort;

import static io.restassured.RestAssured.given;
import static org.hamcrest.Matchers.is;
import static org.springframework.restdocs.restassured3.RestAssuredRestDocumentation.document;

@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
@AutoConfigureRestDocs
class MyUserDocumentationTests {

    @Test
    void listUsers(@Autowired RequestSpecification documentationSpec, @LocalServerPort int port) {
        given(documentationSpec)
            .filter(document("list-users"))
        .when()
            .port(port)
            .get("/")
        .then().assertThat()
            .statusCode(is(200));
    }

}
Kotlin
import io.restassured.RestAssured
import io.restassured.specification.RequestSpecification
import org.hamcrest.Matchers
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.restdocs.AutoConfigureRestDocs
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment
import org.springframework.boot.test.web.server.LocalServerPort
import org.springframework.restdocs.restassured3.RestAssuredRestDocumentation

@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
@AutoConfigureRestDocs
class MyUserDocumentationTests {

    @Test
    fun listUsers(@Autowired documentationSpec: RequestSpecification?, @LocalServerPort port: Int) {
        RestAssured.given(documentationSpec)
            .filter(RestAssuredRestDocumentation.document("list-users"))
            .`when`()
            .port(port)["/"]
            .then().assertThat()
            .statusCode(Matchers.`is`(200))
    }

}

If you require more control over Spring REST Docs configuration than offered by the attributes of @AutoConfigureRestDocs, a RestDocsRestAssuredConfigurationCustomizer bean can be used, as shown in the following example:

Java
import org.springframework.boot.test.autoconfigure.restdocs.RestDocsRestAssuredConfigurationCustomizer;
import org.springframework.boot.test.context.TestConfiguration;
import org.springframework.restdocs.restassured3.RestAssuredRestDocumentationConfigurer;
import org.springframework.restdocs.templates.TemplateFormats;

@TestConfiguration(proxyBeanMethods = false)
public class MyRestDocsConfiguration implements RestDocsRestAssuredConfigurationCustomizer {

    @Override
    public void customize(RestAssuredRestDocumentationConfigurer configurer) {
        configurer.snippets().withTemplateFormat(TemplateFormats.markdown());
    }

}
Kotlin
import org.springframework.boot.test.autoconfigure.restdocs.RestDocsRestAssuredConfigurationCustomizer
import org.springframework.boot.test.context.TestConfiguration
import org.springframework.restdocs.restassured3.RestAssuredRestDocumentationConfigurer
import org.springframework.restdocs.templates.TemplateFormats

@TestConfiguration(proxyBeanMethods = false)
class MyRestDocsConfiguration : RestDocsRestAssuredConfigurationCustomizer {

    override fun customize(configurer: RestAssuredRestDocumentationConfigurer) {
        configurer.snippets().withTemplateFormat(TemplateFormats.markdown())
    }

}
Auto-configured Spring Web Services Tests
Auto-configured Spring Web Services Client Tests

You can use @WebServiceClientTest to test applications that call web services using the Spring Web Services project. By default, it configures a mock WebServiceServer bean and automatically customizes your WebServiceTemplateBuilder. (For more about using Web Services with Spring Boot, see "Web Services".)

A list of the auto-configuration settings that are enabled by @WebServiceClientTest can be found in the appendix.

The following example shows the @WebServiceClientTest annotation in use:

Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.webservices.client.WebServiceClientTest;
import org.springframework.ws.test.client.MockWebServiceServer;
import org.springframework.xml.transform.StringSource;

import static org.assertj.core.api.Assertions.assertThat;
import static org.springframework.ws.test.client.RequestMatchers.payload;
import static org.springframework.ws.test.client.ResponseCreators.withPayload;

@WebServiceClientTest(SomeWebService.class)
class MyWebServiceClientTests {

    @Autowired
    private MockWebServiceServer server;

    @Autowired
    private SomeWebService someWebService;

    @Test
    void mockServerCall() {
        this.server
            .expect(payload(new StringSource("<request/>")))
            .andRespond(withPayload(new StringSource("<response><status>200</status></response>")));
        assertThat(this.someWebService.test())
            .extracting(Response::getStatus)
            .isEqualTo(200);
    }

}
Kotlin
import org.assertj.core.api.Assertions.assertThat
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.webservices.client.WebServiceClientTest
import org.springframework.ws.test.client.MockWebServiceServer
import org.springframework.ws.test.client.RequestMatchers
import org.springframework.ws.test.client.ResponseCreators
import org.springframework.xml.transform.StringSource

@WebServiceClientTest(SomeWebService::class)
class MyWebServiceClientTests(@Autowired val server: MockWebServiceServer, @Autowired val someWebService: SomeWebService) {

    @Test
    fun mockServerCall() {
        server
            .expect(RequestMatchers.payload(StringSource("<request/>")))
            .andRespond(ResponseCreators.withPayload(StringSource("<response><status>200</status></response>")))
        assertThat(this.someWebService.test()).extracting(Response::status).isEqualTo(200)
    }

}
Auto-configured Spring Web Services Server Tests

You can use @WebServiceServerTest to test applications that implement web services using the Spring Web Services project. By default, it configures a MockWebServiceClient bean that can be used to call your web service endpoints. (For more about using Web Services with Spring Boot, see "Web Services".)

A list of the auto-configuration settings that are enabled by @WebServiceServerTest can be found in the appendix.

The following example shows the @WebServiceServerTest annotation in use:

Java
import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.webservices.server.WebServiceServerTest;
import org.springframework.ws.test.server.MockWebServiceClient;
import org.springframework.ws.test.server.RequestCreators;
import org.springframework.ws.test.server.ResponseMatchers;
import org.springframework.xml.transform.StringSource;

@WebServiceServerTest(ExampleEndpoint.class)
class MyWebServiceServerTests {

    @Autowired
    private MockWebServiceClient client;

    @Test
    void mockServerCall() {
        this.client
            .sendRequest(RequestCreators.withPayload(new StringSource("<ExampleRequest/>")))
            .andExpect(ResponseMatchers.payload(new StringSource("<ExampleResponse>42</ExampleResponse>")));
    }

}
Kotlin
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.autoconfigure.webservices.server.WebServiceServerTest
import org.springframework.ws.test.server.MockWebServiceClient
import org.springframework.ws.test.server.RequestCreators
import org.springframework.ws.test.server.ResponseMatchers
import org.springframework.xml.transform.StringSource

@WebServiceServerTest(ExampleEndpoint::class)
class MyWebServiceServerTests(@Autowired val client: MockWebServiceClient) {

    @Test
    fun mockServerCall() {
        client
            .sendRequest(RequestCreators.withPayload(StringSource("<ExampleRequest/>")))
            .andExpect(ResponseMatchers.payload(StringSource("<ExampleResponse>42</ExampleResponse>")))
    }

}
Additional Auto-configuration and Slicing

Each slice provides one or more @AutoConfigure…​ annotations that namely defines the auto-configurations that should be included as part of a slice. Additional auto-configurations can be added on a test-by-test basis by creating a custom @AutoConfigure…​ annotation or by adding @ImportAutoConfiguration to the test as shown in the following example:

Java
import org.springframework.boot.autoconfigure.ImportAutoConfiguration;
import org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration;
import org.springframework.boot.test.autoconfigure.jdbc.JdbcTest;

@JdbcTest
@ImportAutoConfiguration(IntegrationAutoConfiguration.class)
class MyJdbcTests {

}
Kotlin
import org.springframework.boot.autoconfigure.ImportAutoConfiguration
import org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration
import org.springframework.boot.test.autoconfigure.jdbc.JdbcTest

@JdbcTest
@ImportAutoConfiguration(IntegrationAutoConfiguration::class)
class MyJdbcTests
Make sure to not use the regular @Import annotation to import auto-configurations as they are handled in a specific way by Spring Boot.

Alternatively, additional auto-configurations can be added for any use of a slice annotation by registering them in a file stored in META-INF/spring as shown in the following example:

META-INF/spring/org.springframework.boot.test.autoconfigure.jdbc.JdbcTest.imports
com.example.IntegrationAutoConfiguration

In this example, the com.example.IntegrationAutoConfiguration is enabled on every test annotated with @JdbcTest.

You can use comments with # in this file.
A slice or @AutoConfigure…​ annotation can be customized this way as long as it is meta-annotated with @ImportAutoConfiguration.
User Configuration and Slicing

If you structure your code in a sensible way, your @SpringBootApplication class is used by default as the configuration of your tests.

It then becomes important not to litter the application’s main class with configuration settings that are specific to a particular area of its functionality.

Assume that you are using Spring Batch and you rely on the auto-configuration for it. You could define your @SpringBootApplication as follows:

Java
import org.springframework.batch.core.configuration.annotation.EnableBatchProcessing;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
@EnableBatchProcessing
public class MyApplication {

    // ...

}
Kotlin
import org.springframework.batch.core.configuration.annotation.EnableBatchProcessing
import org.springframework.boot.autoconfigure.SpringBootApplication

@SpringBootApplication
@EnableBatchProcessing
class MyApplication {

    // ...

}

Because this class is the source configuration for the test, any slice test actually tries to start Spring Batch, which is definitely not what you want to do. A recommended approach is to move that area-specific configuration to a separate @Configuration class at the same level as your application, as shown in the following example:

Java
import org.springframework.batch.core.configuration.annotation.EnableBatchProcessing;
import org.springframework.context.annotation.Configuration;

@Configuration(proxyBeanMethods = false)
@EnableBatchProcessing
public class MyBatchConfiguration {

    // ...

}
Kotlin
import org.springframework.batch.core.configuration.annotation.EnableBatchProcessing
import org.springframework.context.annotation.Configuration

@Configuration(proxyBeanMethods = false)
@EnableBatchProcessing
class MyBatchConfiguration {

    // ...

}
Depending on the complexity of your application, you may either have a single @Configuration class for your customizations or one class per domain area. The latter approach lets you enable it in one of your tests, if necessary, with the @Import annotation. See this how-to section for more details on when you might want to enable specific @Configuration classes for slice tests.

Test slices exclude @Configuration classes from scanning. For example, for a @WebMvcTest, the following configuration will not include the given WebMvcConfigurer bean in the application context loaded by the test slice:

Java
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration(proxyBeanMethods = false)
public class MyWebConfiguration {

    @Bean
    public WebMvcConfigurer testConfigurer() {
        return new WebMvcConfigurer() {
            // ...
        };
    }

}
Kotlin
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer

@Configuration(proxyBeanMethods = false)
class MyWebConfiguration {

    @Bean
    fun testConfigurer(): WebMvcConfigurer {
        return object : WebMvcConfigurer {
            // ...
        }
    }

}

The configuration below will, however, cause the custom WebMvcConfigurer to be loaded by the test slice.

Java
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Component
public class MyWebMvcConfigurer implements WebMvcConfigurer {

    // ...

}
Kotlin
import org.springframework.stereotype.Component
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer

@Component
class MyWebMvcConfigurer : WebMvcConfigurer {

    // ...

}

Another source of confusion is classpath scanning. Assume that, while you structured your code in a sensible way, you need to scan an additional package. Your application may resemble the following code:

Java
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.ComponentScan;

@SpringBootApplication
@ComponentScan({ "com.example.app", "com.example.another" })
public class MyApplication {

    // ...

}
Kotlin
import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.context.annotation.ComponentScan

@SpringBootApplication
@ComponentScan("com.example.app", "com.example.another")
class MyApplication {

    // ...

}

Doing so effectively overrides the default component scan directive with the side effect of scanning those two packages regardless of the slice that you chose. For instance, a @DataJpaTest seems to suddenly scan components and user configurations of your application. Again, moving the custom directive to a separate class is a good way to fix this issue.

If this is not an option for you, you can create a @SpringBootConfiguration somewhere in the hierarchy of your test so that it is used instead. Alternatively, you can specify a source for your test, which disables the behavior of finding a default one.
Using Spock to Test Spring Boot Applications

Spock 2.x can be used to test a Spring Boot application. To do so, add a dependency on Spock’s spock-spring module to your application’s build. spock-spring integrates Spring’s test framework into Spock. See the documentation for Spock’s Spring module for further details.

7.9.4. Test Utilities

A few test utility classes that are generally useful when testing your application are packaged as part of spring-boot.

ConfigDataApplicationContextInitializer

ConfigDataApplicationContextInitializer is an ApplicationContextInitializer that you can apply to your tests to load Spring Boot application.properties files. You can use it when you do not need the full set of features provided by @SpringBootTest, as shown in the following example:

Java
import org.springframework.boot.test.context.ConfigDataApplicationContextInitializer;
import org.springframework.test.context.ContextConfiguration;

@ContextConfiguration(classes = Config.class, initializers = ConfigDataApplicationContextInitializer.class)
class MyConfigFileTests {

    // ...

}
Kotlin
import org.springframework.boot.test.context.ConfigDataApplicationContextInitializer
import org.springframework.test.context.ContextConfiguration

@ContextConfiguration(classes = [Config::class], initializers = [ConfigDataApplicationContextInitializer::class])
class MyConfigFileTests {

    // ...

}
Using ConfigDataApplicationContextInitializer alone does not provide support for @Value("${…​}") injection. Its only job is to ensure that application.properties files are loaded into Spring’s Environment. For @Value support, you need to either additionally configure a PropertySourcesPlaceholderConfigurer or use @SpringBootTest, which auto-configures one for you.
TestPropertyValues

TestPropertyValues lets you quickly add properties to a ConfigurableEnvironment or ConfigurableApplicationContext. You can call it with key=value strings, as follows:

Java
import org.junit.jupiter.api.Test;

import org.springframework.boot.test.util.TestPropertyValues;
import org.springframework.mock.env.MockEnvironment;

import static org.assertj.core.api.Assertions.assertThat;

class MyEnvironmentTests {

    @Test
    void testPropertySources() {
        MockEnvironment environment = new MockEnvironment();
        TestPropertyValues.of("org=Spring", "name=Boot").applyTo(environment);
        assertThat(environment.getProperty("name")).isEqualTo("Boot");
    }

}
Kotlin
import org.assertj.core.api.Assertions.assertThat
import org.junit.jupiter.api.Test
import org.springframework.boot.test.util.TestPropertyValues
import org.springframework.mock.env.MockEnvironment

class MyEnvironmentTests {

    @Test
    fun testPropertySources() {
        val environment = MockEnvironment()
        TestPropertyValues.of("org=Spring", "name=Boot").applyTo(environment)
        assertThat(environment.getProperty("name")).isEqualTo("Boot")
    }

}
OutputCapture

OutputCapture is a JUnit Extension that you can use to capture System.out and System.err output. To use add @ExtendWith(OutputCaptureExtension.class) and inject CapturedOutput as an argument to your test class constructor or test method as follows:

Java
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;

import org.springframework.boot.test.system.CapturedOutput;
import org.springframework.boot.test.system.OutputCaptureExtension;

import static org.assertj.core.api.Assertions.assertThat;

@ExtendWith(OutputCaptureExtension.class)
class MyOutputCaptureTests {

    @Test
    void testName(CapturedOutput output) {
        System.out.println("Hello World!");
        assertThat(output).contains("World");
    }

}
Kotlin
import org.assertj.core.api.Assertions.assertThat
import org.junit.jupiter.api.Test
import org.junit.jupiter.api.extension.ExtendWith
import org.springframework.boot.test.system.CapturedOutput
import org.springframework.boot.test.system.OutputCaptureExtension

@ExtendWith(OutputCaptureExtension::class)
class MyOutputCaptureTests {

    @Test
    fun testName(output: CapturedOutput?) {
        println("Hello World!")
        assertThat(output).contains("World")
    }

}
TestRestTemplate

TestRestTemplate is a convenience alternative to Spring’s RestTemplate that is useful in integration tests. You can get a vanilla template or one that sends Basic HTTP authentication (with a username and password). In either case, the template is fault tolerant. This means that it behaves in a test-friendly way by not throwing exceptions on 4xx and 5xx errors. Instead, such errors can be detected through the returned ResponseEntity and its status code.

Spring Framework 5.0 provides a new WebTestClient that works for WebFlux integration tests and both WebFlux and MVC end-to-end testing. It provides a fluent API for assertions, unlike TestRestTemplate.

It is recommended, but not mandatory, to use the Apache HTTP Client (version 4.3.2 or better). If you have that on your classpath, the TestRestTemplate responds by configuring the client appropriately. If you do use Apache’s HTTP client, some additional test-friendly features are enabled:

  • Redirects are not followed (so you can assert the response location).

  • Cookies are ignored (so the template is stateless).

TestRestTemplate can be instantiated directly in your integration tests, as shown in the following example:

Java
import org.junit.jupiter.api.Test;

import org.springframework.boot.test.web.client.TestRestTemplate;
import org.springframework.http.ResponseEntity;

import static org.assertj.core.api.Assertions.assertThat;

class MyTests {

    private final TestRestTemplate template = new TestRestTemplate();

    @Test
    void testRequest() {
        ResponseEntity<String> headers = this.template.getForEntity("https://myhost.example.com/example", String.class);
        assertThat(headers.getHeaders().getLocation()).hasHost("other.example.com");
    }

}
Kotlin
import org.assertj.core.api.Assertions.assertThat
import org.junit.jupiter.api.Test
import org.springframework.boot.test.web.client.TestRestTemplate

class MyTests {

    private val template = TestRestTemplate()

    @Test
    fun testRequest() {
        val headers = template.getForEntity("https://myhost.example.com/example", String::class.java)
        assertThat(headers.headers.location).hasHost("other.example.com")
    }

}

Alternatively, if you use the @SpringBootTest annotation with WebEnvironment.RANDOM_PORT or WebEnvironment.DEFINED_PORT, you can inject a fully configured TestRestTemplate and start using it. If necessary, additional customizations can be applied through the RestTemplateBuilder bean. Any URLs that do not specify a host and port automatically connect to the embedded server, as shown in the following example:

Java
import java.time.Duration;

import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.boot.test.context.TestConfiguration;
import org.springframework.boot.test.web.client.TestRestTemplate;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.http.HttpHeaders;

import static org.assertj.core.api.Assertions.assertThat;

@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MySpringBootTests {

    @Autowired
    private TestRestTemplate template;

    @Test
    void testRequest() {
        HttpHeaders headers = this.template.getForEntity("/example", String.class).getHeaders();
        assertThat(headers.getLocation()).hasHost("other.example.com");
    }

    @TestConfiguration(proxyBeanMethods = false)
    static class RestTemplateBuilderConfiguration {

        @Bean
        RestTemplateBuilder restTemplateBuilder() {
            return new RestTemplateBuilder().setConnectTimeout(Duration.ofSeconds(1))
                .setReadTimeout(Duration.ofSeconds(1));
        }

    }

}
Kotlin
import org.assertj.core.api.Assertions.assertThat
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment
import org.springframework.boot.test.context.TestConfiguration
import org.springframework.boot.test.web.client.TestRestTemplate
import org.springframework.boot.web.client.RestTemplateBuilder
import org.springframework.context.annotation.Bean
import java.time.Duration

@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MySpringBootTests(@Autowired val template: TestRestTemplate) {

    @Test
    fun testRequest() {
        val headers = template.getForEntity("/example", String::class.java).headers
        assertThat(headers.location).hasHost("other.example.com")
    }

    @TestConfiguration(proxyBeanMethods = false)
    internal class RestTemplateBuilderConfiguration {

        @Bean
        fun restTemplateBuilder(): RestTemplateBuilder {
            return RestTemplateBuilder().setConnectTimeout(Duration.ofSeconds(1))
                .setReadTimeout(Duration.ofSeconds(1))
        }

    }

}

7.10. Creating Your Own Auto-configuration

If you work in a company that develops shared libraries, or if you work on an open-source or commercial library, you might want to develop your own auto-configuration. Auto-configuration classes can be bundled in external jars and still be picked-up by Spring Boot.

Auto-configuration can be associated to a “starter” that provides the auto-configuration code as well as the typical libraries that you would use with it. We first cover what you need to know to build your own auto-configuration and then we move on to the typical steps required to create a custom starter.

7.10.1. Understanding Auto-configured Beans

Classes that implement auto-configuration are annotated with @AutoConfiguration. This annotation itself is meta-annotated with @Configuration, making auto-configurations standard @Configuration classes. Additional @Conditional annotations are used to constrain when the auto-configuration should apply. Usually, auto-configuration classes use @ConditionalOnClass and @ConditionalOnMissingBean annotations. This ensures that auto-configuration applies only when relevant classes are found and when you have not declared your own @Configuration.

You can browse the source code of spring-boot-autoconfigure to see the @AutoConfiguration classes that Spring provides (see the META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports file).

7.10.2. Locating Auto-configuration Candidates

Spring Boot checks for the presence of a META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports file within your published jar. The file should list your configuration classes, with one class name per line, as shown in the following example:

com.mycorp.libx.autoconfigure.LibXAutoConfiguration
com.mycorp.libx.autoconfigure.LibXWebAutoConfiguration
You can add comments to the imports file using the # character.
Auto-configurations must be loaded only by being named in the imports file. Make sure that they are defined in a specific package space and that they are never the target of component scanning. Furthermore, auto-configuration classes should not enable component scanning to find additional components. Specific @Imports should be used instead.

If your configuration needs to be applied in a specific order, you can use the before, beforeName, after and afterName attributes on the @AutoConfiguration annotation or the dedicated @AutoConfigureBefore and @AutoConfigureAfter annotations. For example, if you provide web-specific configuration, your class may need to be applied after WebMvcAutoConfiguration.

If you want to order certain auto-configurations that should not have any direct knowledge of each other, you can also use @AutoConfigureOrder. That annotation has the same semantic as the regular @Order annotation but provides a dedicated order for auto-configuration classes.

As with standard @Configuration classes, the order in which auto-configuration classes are applied only affects the order in which their beans are defined. The order in which those beans are subsequently created is unaffected and is determined by each bean’s dependencies and any @DependsOn relationships.

7.10.3. Condition Annotations

You almost always want to include one or more @Conditional annotations on your auto-configuration class. The @ConditionalOnMissingBean annotation is one common example that is used to allow developers to override auto-configuration if they are not happy with your defaults.

Spring Boot includes a number of @Conditional annotations that you can reuse in your own code by annotating @Configuration classes or individual @Bean methods. These annotations include:

Class Conditions

The @ConditionalOnClass and @ConditionalOnMissingClass annotations let @Configuration classes be included based on the presence or absence of specific classes. Due to the fact that annotation metadata is parsed by using ASM, you can use the value attribute to refer to the real class, even though that class might not actually appear on the running application classpath. You can also use the name attribute if you prefer to specify the class name by using a String value.

This mechanism does not apply the same way to @Bean methods where typically the return type is the target of the condition: before the condition on the method applies, the JVM will have loaded the class and potentially processed method references which will fail if the class is not present.

To handle this scenario, a separate @Configuration class can be used to isolate the condition, as shown in the following example:

Java
import org.springframework.boot.autoconfigure.AutoConfiguration;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@AutoConfiguration
// Some conditions ...
public class MyAutoConfiguration {

    // Auto-configured beans ...

    @Configuration(proxyBeanMethods = false)
    @ConditionalOnClass(SomeService.class)
    public static class SomeServiceConfiguration {

        @Bean
        @ConditionalOnMissingBean
        public SomeService someService() {
            return new SomeService();
        }

    }

}
Kotlin
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration

@Configuration(proxyBeanMethods = false)
// Some conditions ...
class MyAutoConfiguration {

    // Auto-configured beans ...
    @Configuration(proxyBeanMethods = false)
    @ConditionalOnClass(SomeService::class)
    class SomeServiceConfiguration {

        @Bean
        @ConditionalOnMissingBean
        fun someService(): SomeService {
            return SomeService()
        }

    }

}
If you use @ConditionalOnClass or @ConditionalOnMissingClass as a part of a meta-annotation to compose your own composed annotations, you must use name as referring to the class in such a case is not handled.
Bean Conditions

The @ConditionalOnBean and @ConditionalOnMissingBean annotations let a bean be included based on the presence or absence of specific beans. You can use the value attribute to specify beans by type or name to specify beans by name. The search attribute lets you limit the ApplicationContext hierarchy that should be considered when searching for beans.

When placed on a @Bean method, the target type defaults to the return type of the method, as shown in the following example:

Java
import org.springframework.boot.autoconfigure.AutoConfiguration;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.annotation.Bean;

@AutoConfiguration
public class MyAutoConfiguration {

    @Bean
    @ConditionalOnMissingBean
    public SomeService someService() {
        return new SomeService();
    }

}
Kotlin
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration

@Configuration(proxyBeanMethods = false)
class MyAutoConfiguration {

    @Bean
    @ConditionalOnMissingBean
    fun someService(): SomeService {
        return SomeService()
    }

}

In the preceding example, the someService bean is going to be created if no bean of type SomeService is already contained in the ApplicationContext.

You need to be very careful about the order in which bean definitions are added, as these conditions are evaluated based on what has been processed so far. For this reason, we recommend using only @ConditionalOnBean and @ConditionalOnMissingBean annotations on auto-configuration classes (since these are guaranteed to load after any user-defined bean definitions have been added).
@ConditionalOnBean and @ConditionalOnMissingBean do not prevent @Configuration classes from being created. The only difference between using these conditions at the class level and marking each contained @Bean method with the annotation is that the former prevents registration of the @Configuration class as a bean if the condition does not match.
When declaring a @Bean method, provide as much type information as possible in the method’s return type. For example, if your bean’s concrete class implements an interface the bean method’s return type should be the concrete class and not the interface. Providing as much type information as possible in @Bean methods is particularly important when using bean conditions as their evaluation can only rely upon to type information that is available in the method signature.
Property Conditions

The @ConditionalOnProperty annotation lets configuration be included based on a Spring Environment property. Use the prefix and name attributes to specify the property that should be checked. By default, any property that exists and is not equal to false is matched. You can also create more advanced checks by using the havingValue and matchIfMissing attributes.

Resource Conditions

The @ConditionalOnResource annotation lets configuration be included only when a specific resource is present. Resources can be specified by using the usual Spring conventions, as shown in the following example: file:/home/user/test.dat.

Web Application Conditions

The @ConditionalOnWebApplication and @ConditionalOnNotWebApplication annotations let configuration be included depending on whether the application is a web application. A servlet-based web application is any application that uses a Spring WebApplicationContext, defines a session scope, or has a ConfigurableWebEnvironment. A reactive web application is any application that uses a ReactiveWebApplicationContext, or has a ConfigurableReactiveWebEnvironment.

The @ConditionalOnWarDeployment and @ConditionalOnNotWarDeployment annotations let configuration be included depending on whether the application is a traditional WAR application that is deployed to a servlet container. This condition will not match for applications that are run with an embedded web server.

SpEL Expression Conditions

The @ConditionalOnExpression annotation lets configuration be included based on the result of a SpEL expression.

Referencing a bean in the expression will cause that bean to be initialized very early in context refresh processing. As a result, the bean won’t be eligible for post-processing (such as configuration properties binding) and its state may be incomplete.

7.10.4. Testing your Auto-configuration

An auto-configuration can be affected by many factors: user configuration (@Bean definition and Environment customization), condition evaluation (presence of a particular library), and others. Concretely, each test should create a well defined ApplicationContext that represents a combination of those customizations. ApplicationContextRunner provides a great way to achieve that.

ApplicationContextRunner is usually defined as a field of the test class to gather the base, common configuration. The following example makes sure that MyServiceAutoConfiguration is always invoked:

Java
private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
    .withConfiguration(AutoConfigurations.of(MyServiceAutoConfiguration.class));
Kotlin
val contextRunner = ApplicationContextRunner()
    .withConfiguration(AutoConfigurations.of(MyServiceAutoConfiguration::class.java))
If multiple auto-configurations have to be defined, there is no need to order their declarations as they are invoked in the exact same order as when running the application.

Each test can use the runner to represent a particular use case. For instance, the sample below invokes a user configuration (UserConfiguration) and checks that the auto-configuration backs off properly. Invoking run provides a callback context that can be used with AssertJ.

Java
@Test
void defaultServiceBacksOff() {
    this.contextRunner.withUserConfiguration(UserConfiguration.class).run((context) -> {
        assertThat(context).hasSingleBean(MyService.class);
        assertThat(context).getBean("myCustomService").isSameAs(context.getBean(MyService.class));
    });
}

@Configuration(proxyBeanMethods = false)
static class UserConfiguration {

    @Bean
    MyService myCustomService() {
        return new MyService("mine");
    }

}
Kotlin
@Test
fun defaultServiceBacksOff() {
    contextRunner.withUserConfiguration(UserConfiguration::class.java)
        .run { context: AssertableApplicationContext ->
            assertThat(context).hasSingleBean(MyService::class.java)
            assertThat(context).getBean("myCustomService")
                .isSameAs(context.getBean(MyService::class.java))
        }
}

@Configuration(proxyBeanMethods = false)
internal class UserConfiguration {

    @Bean
    fun myCustomService(): MyService {
        return MyService("mine")
    }

}

It is also possible to easily customize the Environment, as shown in the following example:

Java
@Test
void serviceNameCanBeConfigured() {
    this.contextRunner.withPropertyValues("user.name=test123").run((context) -> {
        assertThat(context).hasSingleBean(MyService.class);
        assertThat(context.getBean(MyService.class).getName()).isEqualTo("test123");
    });
}
Kotlin
@Test
fun serviceNameCanBeConfigured() {
    contextRunner.withPropertyValues("user.name=test123").run { context: AssertableApplicationContext ->
        assertThat(context).hasSingleBean(MyService::class.java)
        assertThat(context.getBean(MyService::class.java).name).isEqualTo("test123")
    }
}

The runner can also be used to display the ConditionEvaluationReport. The report can be printed at INFO or DEBUG level. The following example shows how to use the ConditionEvaluationReportLoggingListener to print the report in auto-configuration tests.

Java
import org.junit.jupiter.api.Test;

import org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener;
import org.springframework.boot.logging.LogLevel;
import org.springframework.boot.test.context.runner.ApplicationContextRunner;

class MyConditionEvaluationReportingTests {

    @Test
    void autoConfigTest() {
        new ApplicationContextRunner()
            .withInitializer(new ConditionEvaluationReportLoggingListener(LogLevel.INFO))
            .run((context) -> {
                    // Test something...
            });
    }

}
Kotlin
import org.junit.jupiter.api.Test
import org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener
import org.springframework.boot.logging.LogLevel
import org.springframework.boot.test.context.assertj.AssertableApplicationContext
import org.springframework.boot.test.context.runner.ApplicationContextRunner

class MyConditionEvaluationReportingTests {

    @Test
    fun autoConfigTest() {
        ApplicationContextRunner()
            .withInitializer(ConditionEvaluationReportLoggingListener(LogLevel.INFO))
            .run { context: AssertableApplicationContext? -> }
    }

}
Simulating a Web Context

If you need to test an auto-configuration that only operates in a servlet or reactive web application context, use the WebApplicationContextRunner or ReactiveWebApplicationContextRunner respectively.

Overriding the Classpath

It is also possible to test what happens when a particular class and/or package is not present at runtime. Spring Boot ships with a FilteredClassLoader that can easily be used by the runner. In the following example, we assert that if MyService is not present, the auto-configuration is properly disabled:

Java
@Test
void serviceIsIgnoredIfLibraryIsNotPresent() {
    this.contextRunner.withClassLoader(new FilteredClassLoader(MyService.class))
        .run((context) -> assertThat(context).doesNotHaveBean("myService"));
}
Kotlin
@Test
fun serviceIsIgnoredIfLibraryIsNotPresent() {
    contextRunner.withClassLoader(FilteredClassLoader(MyService::class.java))
        .run { context: AssertableApplicationContext? ->
            assertThat(context).doesNotHaveBean("myService")
        }
}

7.10.5. Creating Your Own Starter

A typical Spring Boot starter contains code to auto-configure and customize the infrastructure of a given technology, let’s call that "acme". To make it easily extensible, a number of configuration keys in a dedicated namespace can be exposed to the environment. Finally, a single "starter" dependency is provided to help users get started as easily as possible.

Concretely, a custom starter can contain the following:

  • The autoconfigure module that contains the auto-configuration code for "acme".

  • The starter module that provides a dependency to the autoconfigure module as well as "acme" and any additional dependencies that are typically useful. In a nutshell, adding the starter should provide everything needed to start using that library.

This separation in two modules is in no way necessary. If "acme" has several flavors, options or optional features, then it is better to separate the auto-configuration as you can clearly express the fact some features are optional. Besides, you have the ability to craft a starter that provides an opinion about those optional dependencies. At the same time, others can rely only on the autoconfigure module and craft their own starter with different opinions.

If the auto-configuration is relatively straightforward and does not have optional feature, merging the two modules in the starter is definitely an option.

Naming

You should make sure to provide a proper namespace for your starter. Do not start your module names with spring-boot, even if you use a different Maven groupId. We may offer official support for the thing you auto-configure in the future.

As a rule of thumb, you should name a combined module after the starter. For example, assume that you are creating a starter for "acme" and that you name the auto-configure module acme-spring-boot and the starter acme-spring-boot-starter. If you only have one module that combines the two, name it acme-spring-boot-starter.

Configuration keys

If your starter provides configuration keys, use a unique namespace for them. In particular, do not include your keys in the namespaces that Spring Boot uses (such as server, management, spring, and so on). If you use the same namespace, we may modify these namespaces in the future in ways that break your modules. As a rule of thumb, prefix all your keys with a namespace that you own (for example acme).

Make sure that configuration keys are documented by adding field javadoc for each property, as shown in the following example:

Java
import java.time.Duration;

import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties("acme")
public class AcmeProperties {

    /**
     * Whether to check the location of acme resources.
     */
    private boolean checkLocation = true;

    /**
     * Timeout for establishing a connection to the acme server.
     */
    private Duration loginTimeout = Duration.ofSeconds(3);

    // getters/setters ...

    public boolean isCheckLocation() {
        return this.checkLocation;
    }

    public void setCheckLocation(boolean checkLocation) {
        this.checkLocation = checkLocation;
    }

    public Duration getLoginTimeout() {
        return this.loginTimeout;
    }

    public void setLoginTimeout(Duration loginTimeout) {
        this.loginTimeout = loginTimeout;
    }

}
Kotlin
import org.springframework.boot.context.properties.ConfigurationProperties
import java.time.Duration

@ConfigurationProperties("acme")
class AcmeProperties(

    /**
     * Whether to check the location of acme resources.
     */
    var isCheckLocation: Boolean = true,

    /**
     * Timeout for establishing a connection to the acme server.
     */
    var loginTimeout:Duration = Duration.ofSeconds(3))
You should only use plain text with @ConfigurationProperties field Javadoc, since they are not processed before being added to the JSON.

Here are some rules we follow internally to make sure descriptions are consistent:

  • Do not start the description by "The" or "A".

  • For boolean types, start the description with "Whether" or "Enable".

  • For collection-based types, start the description with "Comma-separated list"

  • Use java.time.Duration rather than long and describe the default unit if it differs from milliseconds, such as "If a duration suffix is not specified, seconds will be used".

  • Do not provide the default value in the description unless it has to be determined at runtime.

Make sure to trigger meta-data generation so that IDE assistance is available for your keys as well. You may want to review the generated metadata (META-INF/spring-configuration-metadata.json) to make sure your keys are properly documented. Using your own starter in a compatible IDE is also a good idea to validate that quality of the metadata.

The “autoconfigure” Module

The autoconfigure module contains everything that is necessary to get started with the library. It may also contain configuration key definitions (such as @ConfigurationProperties) and any callback interface that can be used to further customize how the components are initialized.

You should mark the dependencies to the library as optional so that you can include the autoconfigure module in your projects more easily. If you do it that way, the library is not provided and, by default, Spring Boot backs off.

Spring Boot uses an annotation processor to collect the conditions on auto-configurations in a metadata file (META-INF/spring-autoconfigure-metadata.properties). If that file is present, it is used to eagerly filter auto-configurations that do not match, which will improve startup time.

When building with Maven, it is recommended to add the following dependency in a module that contains auto-configurations:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-autoconfigure-processor</artifactId>
    <optional>true</optional>
</dependency>

If you have defined auto-configurations directly in your application, make sure to configure the spring-boot-maven-plugin to prevent the repackage goal from adding the dependency into the fat jar:

<project>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.springframework.boot</groupId>
                            <artifactId>spring-boot-autoconfigure-processor</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

With Gradle, the dependency should be declared in the annotationProcessor configuration, as shown in the following example:

dependencies {
    annotationProcessor "org.springframework.boot:spring-boot-autoconfigure-processor"
}
Starter Module

The starter is really an empty jar. Its only purpose is to provide the necessary dependencies to work with the library. You can think of it as an opinionated view of what is required to get started.

Do not make assumptions about the project in which your starter is added. If the library you are auto-configuring typically requires other starters, mention them as well. Providing a proper set of default dependencies may be hard if the number of optional dependencies is high, as you should avoid including dependencies that are unnecessary for a typical usage of the library. In other words, you should not include optional dependencies.

Either way, your starter must reference the core Spring Boot starter (spring-boot-starter) directly or indirectly (there is no need to add it if your starter relies on another starter). If a project is created with only your custom starter, Spring Boot’s core features will be honoured by the presence of the core starter.

7.11. Kotlin Support

Kotlin is a statically-typed language targeting the JVM (and other platforms) which allows writing concise and elegant code while providing interoperability with existing libraries written in Java.

Spring Boot provides Kotlin support by leveraging the support in other Spring projects such as Spring Framework, Spring Data, and Reactor. See the Spring Framework Kotlin support documentation for more information.

The easiest way to start with Spring Boot and Kotlin is to follow this comprehensive tutorial. You can create new Kotlin projects by using start.spring.io. Feel free to join the #spring channel of Kotlin Slack or ask a question with the spring and kotlin tags on Stack Overflow if you need support.

7.11.1. Requirements

Spring Boot requires at least Kotlin 1.3.x and manages a suitable Kotlin version through dependency management. To use Kotlin, org.jetbrains.kotlin:kotlin-stdlib and org.jetbrains.kotlin:kotlin-reflect must be present on the classpath. The kotlin-stdlib variants kotlin-stdlib-jdk7 and kotlin-stdlib-jdk8 can also be used.

Since Kotlin classes are final by default, you are likely to want to configure kotlin-spring plugin in order to automatically open Spring-annotated classes so that they can be proxied.

Jackson’s Kotlin module is required for serializing / deserializing JSON data in Kotlin. It is automatically registered when found on the classpath. A warning message is logged if Jackson and Kotlin are present but the Jackson Kotlin module is not.

These dependencies and plugins are provided by default if one bootstraps a Kotlin project on start.spring.io.

7.11.2. Null-safety

One of Kotlin’s key features is null-safety. It deals with null values at compile time rather than deferring the problem to runtime and encountering a NullPointerException. This helps to eliminate a common source of bugs without paying the cost of wrappers like Optional. Kotlin also allows using functional constructs with nullable values as described in this comprehensive guide to null-safety in Kotlin.

Although Java does not allow one to express null-safety in its type system, Spring Framework, Spring Data, and Reactor now provide null-safety of their API through tooling-friendly annotations. By default, types from Java APIs used in Kotlin are recognized as platform types for which null-checks are relaxed. Kotlin’s support for JSR 305 annotations combined with nullability annotations provide null-safety for the related Spring API in Kotlin.

The JSR 305 checks can be configured by adding the -Xjsr305 compiler flag with the following options: -Xjsr305={strict|warn|ignore}. The default behavior is the same as -Xjsr305=warn. The strict value is required to have null-safety taken in account in Kotlin types inferred from Spring API but should be used with the knowledge that Spring API nullability declaration could evolve even between minor releases and more checks may be added in the future).

Generic type arguments, varargs and array elements nullability are not yet supported. See SPR-15942 for up-to-date information. Also be aware that Spring Boot’s own API is not yet annotated.

7.11.3. Kotlin API

runApplication

Spring Boot provides an idiomatic way to run an application with runApplication<MyApplication>(*args) as shown in the following example:

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

@SpringBootApplication
class MyApplication

fun main(args: Array<String>) {
    runApplication<MyApplication>(*args)
}

This is a drop-in replacement for SpringApplication.run(MyApplication::class.java, *args). It also allows customization of the application as shown in the following example:

runApplication<MyApplication>(*args) {
    setBannerMode(OFF)
}
Extensions

Kotlin extensions provide the ability to extend existing classes with additional functionality. The Spring Boot Kotlin API makes use of these extensions to add new Kotlin specific conveniences to existing APIs.

TestRestTemplate extensions, similar to those provided by Spring Framework for RestOperations in Spring Framework, are provided. Among other things, the extensions make it possible to take advantage of Kotlin reified type parameters.

7.11.4. Dependency management

In order to avoid mixing different versions of Kotlin dependencies on the classpath, Spring Boot imports the Kotlin BOM.

With Maven, the Kotlin version can be customized by setting the kotlin.version property and plugin management is provided for kotlin-maven-plugin. With Gradle, the Spring Boot plugin automatically aligns the kotlin.version with the version of the Kotlin plugin.

Spring Boot also manages the version of Coroutines dependencies by importing the Kotlin Coroutines BOM. The version can be customized by setting the kotlin-coroutines.version property.

org.jetbrains.kotlinx:kotlinx-coroutines-reactor dependency is provided by default if one bootstraps a Kotlin project with at least one reactive dependency on start.spring.io.

7.11.5. @ConfigurationProperties

@ConfigurationProperties when used in combination with @ConstructorBinding supports classes with immutable val properties as shown in the following example:

@ConstructorBinding
@ConfigurationProperties("example.kotlin")
data class KotlinExampleProperties(
        val name: String,
        val description: String,
        val myService: MyService) {

    data class MyService(
            val apiToken: String,
            val uri: URI
    )
}
To generate your own metadata using the annotation processor, kapt should be configured with the spring-boot-configuration-processor dependency. Note that some features (such as detecting the default value or deprecated items) are not working due to limitations in the model kapt provides.

7.11.6. Testing

While it is possible to use JUnit 4 to test Kotlin code, JUnit 5 is provided by default and is recommended. JUnit 5 enables a test class to be instantiated once and reused for all of the class’s tests. This makes it possible to use @BeforeAll and @AfterAll annotations on non-static methods, which is a good fit for Kotlin.

To mock Kotlin classes, MockK is recommended. If you need the MockK equivalent of the Mockito specific @MockBean and @SpyBean annotations, you can use SpringMockK which provides similar @MockkBean and @SpykBean annotations.

7.11.7. Resources

Examples

7.12. What to Read Next

If you want to learn more about any of the classes discussed in this section, see the Spring Boot API documentation or you can browse the source code directly. If you have specific questions, see the how-to section.

If you are comfortable with Spring Boot’s core features, you can continue on and read about production-ready features.

8. Web

Spring Boot is well suited for web application development. You can create a self-contained HTTP server by using embedded Tomcat, Jetty, Undertow, or Netty. Most web applications use the spring-boot-starter-web module to get up and running quickly. You can also choose to build reactive web applications by using the spring-boot-starter-webflux module.

If you have not yet developed a Spring Boot web application, you can follow the "Hello World!" example in the Getting started section.

8.1. Servlet Web Applications

If you want to build servlet-based web applications, you can take advantage of Spring Boot’s auto-configuration for Spring MVC or Jersey.

8.1.1. The “Spring Web MVC Framework”

The Spring Web MVC framework (often referred to as “Spring MVC”) is a rich “model view controller” web framework. Spring MVC lets you create special @Controller or @RestController beans to handle incoming HTTP requests. Methods in your controller are mapped to HTTP by using @RequestMapping annotations.

The following code shows a typical @RestController that serves JSON data:

Java
import java.util.List;

import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/users")
public class MyRestController {

    private final UserRepository userRepository;

    private final CustomerRepository customerRepository;

    public MyRestController(UserRepository userRepository, CustomerRepository customerRepository) {
        this.userRepository = userRepository;
        this.customerRepository = customerRepository;
    }

    @GetMapping("/{userId}")
    public User getUser(@PathVariable Long userId) {
        return this.userRepository.findById(userId).get();
    }

    @GetMapping("/{userId}/customers")
    public List<Customer> getUserCustomers(@PathVariable Long userId) {
        return this.userRepository.findById(userId).map(this.customerRepository::findByUser).get();
    }

    @DeleteMapping("/{userId}")
    public void deleteUser(@PathVariable Long userId) {
        this.userRepository.deleteById(userId);
    }

}
Kotlin
import org.springframework.web.bind.annotation.DeleteMapping
import org.springframework.web.bind.annotation.GetMapping
import org.springframework.web.bind.annotation.PathVariable
import org.springframework.web.bind.annotation.RequestMapping
import org.springframework.web.bind.annotation.RestController


@RestController
@RequestMapping("/users")
class MyRestController(private val userRepository: UserRepository, private val customerRepository: CustomerRepository) {

    @GetMapping("/{userId}")
    fun getUser(@PathVariable userId: Long): User {
        return userRepository.findById(userId).get()
    }

    @GetMapping("/{userId}/customers")
    fun getUserCustomers(@PathVariable userId: Long): List<Customer> {
        return userRepository.findById(userId).map(customerRepository::findByUser).get()
    }

    @DeleteMapping("/{userId}")
    fun deleteUser(@PathVariable userId: Long) {
        userRepository.deleteById(userId)
    }

}

“WebMvc.fn”, the functional variant, separates the routing configuration from the actual handling of the requests, as shown in the following example:

Java
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.MediaType;
import org.springframework.web.servlet.function.RequestPredicate;
import org.springframework.web.servlet.function.RouterFunction;
import org.springframework.web.servlet.function.ServerResponse;

import static org.springframework.web.servlet.function.RequestPredicates.accept;
import static org.springframework.web.servlet.function.RouterFunctions.route;

@Configuration(proxyBeanMethods = false)
public class MyRoutingConfiguration {

    private static final RequestPredicate ACCEPT_JSON = accept(MediaType.APPLICATION_JSON);

    @Bean
    public RouterFunction<ServerResponse> routerFunction(MyUserHandler userHandler) {
        return route()
                .GET("/{user}", ACCEPT_JSON, userHandler::getUser)
                .GET("/{user}/customers", ACCEPT_JSON, userHandler::getUserCustomers)
                .DELETE("/{user}", ACCEPT_JSON, userHandler::deleteUser)
                .build();
    }

}
Kotlin
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import org.springframework.http.MediaType
import org.springframework.web.servlet.function.RequestPredicates.accept
import org.springframework.web.servlet.function.RouterFunction
import org.springframework.web.servlet.function.RouterFunctions
import org.springframework.web.servlet.function.ServerResponse

@Configuration(proxyBeanMethods = false)
class MyRoutingConfiguration {

    @Bean
    fun routerFunction(userHandler: MyUserHandler): RouterFunction<ServerResponse> {
        return RouterFunctions.route()
            .GET("/{user}", ACCEPT_JSON, userHandler::getUser)
            .GET("/{user}/customers", ACCEPT_JSON, userHandler::getUserCustomers)
            .DELETE("/{user}", ACCEPT_JSON, userHandler::deleteUser)
            .build()
    }

    companion object {
        private val ACCEPT_JSON = accept(MediaType.APPLICATION_JSON)
    }

}
Java
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.function.ServerRequest;
import org.springframework.web.servlet.function.ServerResponse;

@Component
public class MyUserHandler {

    public ServerResponse getUser(ServerRequest request) {
        ...
        return ServerResponse.ok().build();
    }

    public ServerResponse getUserCustomers(ServerRequest request) {
        ...
        return ServerResponse.ok().build();
    }

    public ServerResponse deleteUser(ServerRequest request) {
        ...
        return ServerResponse.ok().build();
    }

}
Kotlin
import org.springframework.stereotype.Component
import org.springframework.web.servlet.function.ServerRequest
import org.springframework.web.servlet.function.ServerResponse

@Component
class MyUserHandler {

    fun getUser(request: ServerRequest?): ServerResponse {
        return ServerResponse.ok().build()
    }

    fun getUserCustomers(request: ServerRequest?): ServerResponse {
        return ServerResponse.ok().build()
    }

    fun deleteUser(request: ServerRequest?): ServerResponse {
        return ServerResponse.ok().build()
    }

}

Spring MVC is part of the core Spring Framework, and detailed information is available in the reference documentation. There are also several guides that cover Spring MVC available at spring.io/guides.

You can define as many RouterFunction beans as you like to modularize the definition of the router. Beans can be ordered if you need to apply a precedence.
Spring MVC Auto-configuration

Spring Boot provides auto-configuration for Spring MVC that works well with most applications. It replaces the need for @EnableWebMvc and the two cannot be used together. In addition to Spring MVC’s defaults, the auto-configuration provides the following features:

  • Inclusion of ContentNegotiatingViewResolver and BeanNameViewResolver beans.

  • Support for serving static resources, including support for WebJars (covered later in this document).

  • Automatic registration of Converter, GenericConverter, and Formatter beans.

  • Support for HttpMessageConverters (covered later in this document).

  • Automatic registration of MessageCodesResolver (covered later in this document).

  • Static index.html support.

  • Automatic use of a ConfigurableWebBindingInitializer bean (covered later in this document).

If you want to keep those Spring Boot MVC customizations and make more MVC customizations (interceptors, formatters, view controllers, and other features), you can add your own @Configuration class of type WebMvcConfigurer but without @EnableWebMvc.

If you want to provide custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter, or ExceptionHandlerExceptionResolver, and still keep the Spring Boot MVC customizations, you can declare a bean of type WebMvcRegistrations and use it to provide custom instances of those components. The custom instances will be subject to further initialization and configuration by Spring MVC. To participate in, and if desired, override that subsequent processing, a WebMvcConfigurer should be used.

If you do not want to use the auto-configuration and want to take complete control of Spring MVC, add your own @Configuration annotated with @EnableWebMvc. Alternatively, add your own @Configuration-annotated DelegatingWebMvcConfiguration as described in the Javadoc of @EnableWebMvc.

Spring MVC Conversion Service

Spring MVC uses a different ConversionService to the one used to convert values from your application.properties or application.yaml file. It means that Period, Duration and DataSize converters are not available and that @DurationUnit and @DataSizeUnit annotations will be ignored.

If you want to customize the ConversionService used by Spring MVC, you can provide a WebMvcConfigurer bean with an addFormatters method. From this method you can register any converter that you like, or you can delegate to the static methods available on ApplicationConversionService.

Conversion can also be customized using the spring.mvc.format.* configuration properties. When not configured, the following defaults are used:

Property DateTimeFormatter

spring.mvc.format.date

ofLocalizedDate(FormatStyle.SHORT)

spring.mvc.format.time

ofLocalizedTime(FormatStyle.SHORT)

spring.mvc.format.date-time

ofLocalizedDateTime(FormatStyle.SHORT)

HttpMessageConverters

Spring MVC uses the HttpMessageConverter interface to convert HTTP requests and responses. Sensible defaults are included out of the box. For example, objects can be automatically converted to JSON (by using the Jackson library) or XML (by using the Jackson XML extension, if available, or by using JAXB if the Jackson XML extension is not available). By default, strings are encoded in UTF-8.

If you need to add or customize converters, you can use Spring Boot’s HttpMessageConverters class, as shown in the following listing:

Java
import org.springframework.boot.autoconfigure.http.HttpMessageConverters;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.converter.HttpMessageConverter;

@Configuration(proxyBeanMethods = false)
public class MyHttpMessageConvertersConfiguration {

    @Bean
    public HttpMessageConverters customConverters() {
        HttpMessageConverter<?> additional = new AdditionalHttpMessageConverter();
        HttpMessageConverter<?> another = new AnotherHttpMessageConverter();
        return new HttpMessageConverters(additional, another);
    }

}
Kotlin
import org.springframework.boot.autoconfigure.http.HttpMessageConverters
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import org.springframework.http.converter.HttpMessageConverter

@Configuration(proxyBeanMethods = false)
class MyHttpMessageConvertersConfiguration {

    @Bean
    fun customConverters(): HttpMessageConverters {
        val additional: HttpMessageConverter<*> = AdditionalHttpMessageConverter()
        val another: HttpMessageConverter<*> = AnotherHttpMessageConverter()
        return HttpMessageConverters(additional, another)
    }

}

Any HttpMessageConverter bean that is present in the context is added to the list of converters. You can also override default converters in the same way.

MessageCodesResolver

Spring MVC has a strategy for generating error codes for rendering error messages from binding errors: MessageCodesResolver. If you set the spring.mvc.message-codes-resolver-format property PREFIX_ERROR_CODE or POSTFIX_ERROR_CODE, Spring Boot creates one for you (see the enumeration in DefaultMessageCodesResolver.Format).

Static Content

By default, Spring Boot serves static content from a directory called /static (or /public or /resources or /META-INF/resources) in the classpath or from the root of the ServletContext. It uses the ResourceHttpRequestHandler from Spring MVC so that you can modify that behavior by adding your own WebMvcConfigurer and overriding the addResourceHandlers method.

In a stand-alone web application, the default servlet from the container is not enabled. It can be enabled using the server.servlet.register-default-servlet property.

The default servlet acts as a fallback, serving content from the root of the ServletContext if Spring decides not to handle it. Most of the time, this does not happen (unless you modify the default MVC configuration), because Spring can always handle requests through the DispatcherServlet.

By default, resources are mapped on /**, but you can tune that with the spring.mvc.static-path-pattern property. For instance, relocating all resources to /resources/** can be achieved as follows:

Properties
spring.mvc.static-path-pattern=/resources/**
Yaml
spring:
  mvc:
    static-path-pattern: "/resources/**"

You can also customize the static resource locations by using the spring.web.resources.static-locations property (replacing the default values with a list of directory locations). The root servlet context path, "/", is automatically added as a location as well.

In addition to the “standard” static resource locations mentioned earlier, a special case is made for Webjars content. Any resources with a path in /webjars/** are served from jar files if they are packaged in the Webjars format.

Do not use the src/main/webapp directory if your application is packaged as a jar. Although this directory is a common standard, it works only with war packaging, and it is silently ignored by most build tools if you generate a jar.

Spring Boot also supports the advanced resource handling features provided by Spring MVC, allowing use cases such as cache-busting static resources or using version agnostic URLs for Webjars.

To use version agnostic URLs for Webjars, add the webjars-locator-core dependency. Then declare your Webjar. Using jQuery as an example, adding "/webjars/jquery/jquery.min.js" results in "/webjars/jquery/x.y.z/jquery.min.js" where x.y.z is the Webjar version.

If you use JBoss, you need to declare the webjars-locator-jboss-vfs dependency instead of the webjars-locator-core. Otherwise, all Webjars resolve as a 404.

To use cache busting, the following configuration configures a cache busting solution for all static resources, effectively adding a content hash, such as <link href="/css/spring-2a2d595e6ed9a0b24f027f2b63b134d6.css"/>, in URLs:

Properties
spring.web.resources.chain.strategy.content.enabled=true
spring.web.resources.chain.strategy.content.paths=/**
Yaml
spring:
  web:
    resources:
      chain:
        strategy:
          content:
            enabled: true
            paths: "/**"
Links to resources are rewritten in templates at runtime, thanks to a ResourceUrlEncodingFilter that is auto-configured for Thymeleaf and FreeMarker. You should manually declare this filter when using JSPs. Other template engines are currently not automatically supported but can be with custom template macros/helpers and the use of the ResourceUrlProvider.

When loading resources dynamically with, for example, a JavaScript module loader, renaming files is not an option. That is why other strategies are also supported and can be combined. A "fixed" strategy adds a static version string in the URL without changing the file name, as shown in the following example:

Properties
spring.web.resources.chain.strategy.content.enabled=true
spring.web.resources.chain.strategy.content.paths=/**
spring.web.resources.chain.strategy.fixed.enabled=true
spring.web.resources.chain.strategy.fixed.paths=/js/lib/
spring.web.resources.chain.strategy.fixed.version=v12
Yaml
spring:
  web:
    resources:
      chain:
        strategy:
          content:
            enabled: true
            paths: "/**"
          fixed:
            enabled: true
            paths: "/js/lib/"
            version: "v12"

With this configuration, JavaScript modules located under "/js/lib/" use a fixed versioning strategy ("/v12/js/lib/mymodule.js"), while other resources still use the content one (<link href="/css/spring-2a2d595e6ed9a0b24f027f2b63b134d6.css"/>).

See WebProperties.Resources for more supported options.

This feature has been thoroughly described in a dedicated blog post and in Spring Framework’s reference documentation.

Welcome Page

Spring Boot supports both static and templated welcome pages. It first looks for an index.html file in the configured static content locations. If one is not found, it then looks for an index template. If either is found, it is automatically used as the welcome page of the application.

Custom Favicon

As with other static resources, Spring Boot checks for a favicon.ico in the configured static content locations. If such a file is present, it is automatically used as the favicon of the application.

Path Matching and Content Negotiation

Spring MVC can map incoming HTTP requests to handlers by looking at the request path and matching it to the mappings defined in your application (for example, @GetMapping annotations on Controller methods).

Spring Boot chooses to disable suffix pattern matching by default, which means that requests like "GET /projects/spring-boot.json" will not be matched to @GetMapping("/projects/spring-boot") mappings. This is considered as a best practice for Spring MVC applications. This feature was mainly useful in the past for HTTP clients which did not send proper "Accept" request headers; we needed to make sure to send the correct Content Type to the client. Nowadays, Content Negotiation is much more reliable.

There are other ways to deal with HTTP clients that do not consistently send proper "Accept" request headers. Instead of using suffix matching, we can use a query parameter to ensure that requests like "GET /projects/spring-boot?format=json" will be mapped to @GetMapping("/projects/spring-boot"):

Properties
spring.mvc.contentnegotiation.favor-parameter=true
Yaml
spring:
  mvc:
    contentnegotiation:
      favor-parameter: true

Or if you prefer to use a different parameter name:

Properties
spring.mvc.contentnegotiation.favor-parameter=true
spring.mvc.contentnegotiation.parameter-name=myparam
Yaml
spring:
  mvc:
    contentnegotiation:
      favor-parameter: true
      parameter-name: "myparam"

Most standard media types are supported out-of-the-box, but you can also define new ones:

Properties
spring.mvc.contentnegotiation.media-types.markdown=text/markdown
Yaml
spring:
  mvc:
    contentnegotiation:
      media-types:
        markdown: "text/markdown"

Suffix pattern matching is deprecated and will be removed in a future release. If you understand the caveats and would still like your application to use suffix pattern matching, the following configuration is required:

Properties
spring.mvc.contentnegotiation.favor-path-extension=true
spring.mvc.pathmatch.use-suffix-pattern=true
Yaml
spring:
  mvc:
    contentnegotiation:
      favor-path-extension: true
    pathmatch:
      use-suffix-pattern: true

Alternatively, rather than open all suffix patterns, it is more secure to only support registered suffix patterns:

Properties
spring.mvc.contentnegotiation.favor-path-extension=true
spring.mvc.pathmatch.use-registered-suffix-pattern=true
Yaml
spring:
  mvc:
    contentnegotiation:
      favor-path-extension: true
    pathmatch:
      use-registered-suffix-pattern: true

As of Spring Framework 5.3, Spring MVC supports two strategies for matching request paths to controllers. By default, Spring Boot uses the PathPatternParser strategy. PathPatternParser is an optimized implementation but comes with some restrictions compared to the AntPathMatcher strategy. PathPatternParser restricts usage of some path pattern variants. It is also incompatible with suffix pattern matching (spring.mvc.pathmatch.use-suffix-pattern, spring.mvc.pathmatch.use-registered-suffix-pattern) and configuring the DispatcherServlet with a path prefix (spring.mvc.servlet.path).

The strategy can be configured using the spring.mvc.pathmatch.matching-strategy configuration property, as shown in the following example:

Properties
spring.mvc.pathmatch.matching-strategy=ant-path-matcher
Yaml
spring:
  mvc:
    pathmatch:
      matching-strategy: "ant-path-matcher"

By default, Spring MVC will send a 404 Not Found error response if a handler is not found for a request. To have a NoHandlerFoundException thrown instead, set configprop:spring.mvc.throw-exception-if-no-handler-found to true. Note that, by default, the serving of static content is mapped to /** and will, therefore, provide a handler for all requests. For a NoHandlerFoundException to be thrown, you must also set spring.mvc.static-path-pattern to a more specific value such as /resources/** or set spring.web.resources.add-mappings to false to disable serving of static content entirely.

ConfigurableWebBindingInitializer

Spring MVC uses a WebBindingInitializer to initialize a WebDataBinder for a particular request. If you create your own ConfigurableWebBindingInitializer @Bean, Spring Boot automatically configures Spring MVC to use it.

Template Engines

As well as REST web services, you can also use Spring MVC to serve dynamic HTML content. Spring MVC supports a variety of templating technologies, including Thymeleaf, FreeMarker, and JSPs. Also, many other templating engines include their own Spring MVC integrations.

Spring Boot includes auto-configuration support for the following templating engines:

If possible, JSPs should be avoided. There are several known limitations when using them with embedded servlet containers.

When you use one of these templating engines with the default configuration, your templates are picked up automatically from src/main/resources/templates.

Depending on how you run your application, your IDE may order the classpath differently. Running your application in the IDE from its main method results in a different ordering than when you run your application by using Maven or Gradle or from its packaged jar. This can cause Spring Boot to fail to find the expected template. If you have this problem, you can reorder the classpath in the IDE to place the module’s classes and resources first.
Error Handling

By default, Spring Boot provides an /error mapping that handles all errors in a sensible way, and it is registered as a “global” error page in the servlet container. For machine clients, it produces a JSON response with details of the error, the HTTP status, and the exception message. For browser clients, there is a “whitelabel” error view that renders the same data in HTML format (to customize it, add a View that resolves to error).

There are a number of server.error properties that can be set if you want to customize the default error handling behavior. See the “Server Properties” section of the Appendix.

To replace the default behavior completely, you can implement ErrorController and register a bean definition of that type or add a bean of type ErrorAttributes to use the existing mechanism but replace the contents.

The BasicErrorController can be used as a base class for a custom ErrorController. This is particularly useful if you want to add a handler for a new content type (the default is to handle text/html specifically and provide a fallback for everything else). To do so, extend BasicErrorController, add a public method with a @RequestMapping that has a produces attribute, and create a bean of your new type.

You can also define a class annotated with @ControllerAdvice to customize the JSON document to return for a particular controller and/or exception type, as shown in the following example:

Java
import javax.servlet.RequestDispatcher;
import javax.servlet.http.HttpServletRequest;

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.servlet.mvc.method.annotation.ResponseEntityExceptionHandler;

@ControllerAdvice(basePackageClasses = SomeController.class)
public class MyControllerAdvice extends ResponseEntityExceptionHandler {

    @ResponseBody
    @ExceptionHandler(MyException.class)
    public ResponseEntity<?> handleControllerException(HttpServletRequest request, Throwable ex) {
        HttpStatus status = getStatus(request);
        return new ResponseEntity<>(new MyErrorBody(status.value(), ex.getMessage()), status);
    }

    private HttpStatus getStatus(HttpServletRequest request) {
        Integer code = (Integer) request.getAttribute(RequestDispatcher.ERROR_STATUS_CODE);
        HttpStatus status = HttpStatus.resolve(code);
        return (status != null) ? status : HttpStatus.INTERNAL_SERVER_ERROR;
    }

}
Kotlin
import org.springframework.http.HttpStatus
import org.springframework.http.ResponseEntity
import org.springframework.web.bind.annotation.ControllerAdvice
import org.springframework.web.bind.annotation.ExceptionHandler
import org.springframework.web.bind.annotation.ResponseBody
import org.springframework.web.servlet.mvc.method.annotation.ResponseEntityExceptionHandler
import javax.servlet.RequestDispatcher
import javax.servlet.http.HttpServletRequest

@ControllerAdvice(basePackageClasses = [SomeController::class])
class MyControllerAdvice : ResponseEntityExceptionHandler() {

    @ResponseBody
    @ExceptionHandler(MyException::class)
    fun handleControllerException(request: HttpServletRequest, ex: Throwable): ResponseEntity<*> {
        val status = getStatus(request)
        return ResponseEntity(MyErrorBody(status.value(), ex.message), status)
    }

    private fun getStatus(request: HttpServletRequest): HttpStatus {
        val code = request.getAttribute(RequestDispatcher.ERROR_STATUS_CODE) as Int
        val status = HttpStatus.resolve(code)
        return status ?: HttpStatus.INTERNAL_SERVER_ERROR
    }

}

In the preceding example, if MyException is thrown by a controller defined in the same package as SomeController, a JSON representation of the MyErrorBody POJO is used instead of the ErrorAttributes representation.

In some cases, errors handled at the controller level are not recorded by the metrics infrastructure. Applications can ensure that such exceptions are recorded with the request metrics by setting the handled exception as a request attribute:

Java
import javax.servlet.http.HttpServletRequest;

import org.springframework.boot.web.servlet.error.ErrorAttributes;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ExceptionHandler;

@Controller
public class MyController {

    @ExceptionHandler(CustomException.class)
    String handleCustomException(HttpServletRequest request, CustomException ex) {
        request.setAttribute(ErrorAttributes.ERROR_ATTRIBUTE, ex);
        return "errorView";
    }

}
Kotlin
import org.springframework.boot.web.servlet.error.ErrorAttributes
import org.springframework.stereotype.Controller
import org.springframework.web.bind.annotation.ExceptionHandler
import javax.servlet.http.HttpServletRequest

@Controller
class MyController {

    @ExceptionHandler(CustomException::class)
    fun handleCustomException(request: HttpServletRequest, ex: CustomException?): String {
        request.setAttribute(ErrorAttributes.ERROR_ATTRIBUTE, ex)
        return "errorView"
    }

}
Custom Error Pages

If you want to display a custom HTML error page for a given status code, you can add a file to an /error directory. Error pages can either be static HTML (that is, added under any of the static resource directories) or be built by using templates. The name of the file should be the exact status code or a series mask.

For example, to map 404 to a static HTML file, your directory structure would be as follows:

src/
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- public/
             +- error/
             |   +- 404.html
             +- <other public assets>

To map all 5xx errors by using a FreeMarker template, your directory structure would be as follows:

src/
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- templates/
             +- error/
             |   +- 5xx.ftlh
             +- <other templates>

For more complex mappings, you can also add beans that implement the ErrorViewResolver interface, as shown in the following example:

Java
import java.util.Map;

import javax.servlet.http.HttpServletRequest;

import org.springframework.boot.autoconfigure.web.servlet.error.ErrorViewResolver;
import org.springframework.http.HttpStatus;
import org.springframework.web.servlet.ModelAndView;

public class MyErrorViewResolver implements ErrorViewResolver {

    @Override
    public ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status, Map<String, Object> model) {
        // Use the request or status to optionally return a ModelAndView
        if (status == HttpStatus.INSUFFICIENT_STORAGE) {
            // We could add custom model values here
            new ModelAndView("myview");
        }
        return null;
    }

}
Kotlin
import org.springframework.boot.autoconfigure.web.servlet.error.ErrorViewResolver
import org.springframework.http.HttpStatus
import org.springframework.web.servlet.ModelAndView
import javax.servlet.http.HttpServletRequest

class MyErrorViewResolver : ErrorViewResolver {

    override fun resolveErrorView(request: HttpServletRequest, status: HttpStatus,
            model: Map<String, Any>): ModelAndView? {
        // Use the request or status to optionally return a ModelAndView
        if (status == HttpStatus.INSUFFICIENT_STORAGE) {
            // We could add custom model values here
            return ModelAndView("myview")
        }
        return null
    }

}

You can also use regular Spring MVC features such as @ExceptionHandler methods and @ControllerAdvice. The ErrorController then picks up any unhandled exceptions.

Mapping Error Pages Outside of Spring MVC

For applications that do not use Spring MVC, you can use the ErrorPageRegistrar interface to directly register ErrorPages. This abstraction works directly with the underlying embedded servlet container and works even if you do not have a Spring MVC DispatcherServlet.

Java
import org.springframework.boot.web.server.ErrorPage;
import org.springframework.boot.web.server.ErrorPageRegistrar;
import org.springframework.boot.web.server.ErrorPageRegistry;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.HttpStatus;

@Configuration(proxyBeanMethods = false)
public class MyErrorPagesConfiguration {

    @Bean
    public ErrorPageRegistrar errorPageRegistrar() {
        return this::registerErrorPages;
    }

    private void registerErrorPages(ErrorPageRegistry registry) {
        registry.addErrorPages(new ErrorPage(HttpStatus.BAD_REQUEST, "/400"));
    }

}
Kotlin
import org.springframework.boot.web.server.ErrorPage
import org.springframework.boot.web.server.ErrorPageRegistrar
import org.springframework.boot.web.server.ErrorPageRegistry
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import org.springframework.http.HttpStatus

@Configuration(proxyBeanMethods = false)
class MyErrorPagesConfiguration {

    @Bean
    fun errorPageRegistrar(): ErrorPageRegistrar {
        return ErrorPageRegistrar { registry: ErrorPageRegistry -> registerErrorPages(registry) }
    }

    private fun registerErrorPages(registry: ErrorPageRegistry) {
        registry.addErrorPages(ErrorPage(HttpStatus.BAD_REQUEST, "/400"))
    }

}
If you register an ErrorPage with a path that ends up being handled by a Filter (as is common with some non-Spring web frameworks, like Jersey and Wicket), then the Filter has to be explicitly registered as an ERROR dispatcher, as shown in the following example:
Java
import java.util.EnumSet;

import javax.servlet.DispatcherType;

import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration(proxyBeanMethods = false)
public class MyFilterConfiguration {

    @Bean
    public FilterRegistrationBean<MyFilter> myFilter() {
        FilterRegistrationBean<MyFilter> registration = new FilterRegistrationBean<>(new MyFilter());
        // ...
        registration.setDispatcherTypes(EnumSet.allOf(DispatcherType.class));
        return registration;
    }

}
Kotlin
import org.springframework.boot.web.servlet.FilterRegistrationBean
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import java.util.EnumSet
import javax.servlet.DispatcherType

@Configuration(proxyBeanMethods = false)
class MyFilterConfiguration {

    @Bean
    fun myFilter(): FilterRegistrationBean<MyFilter> {
        val registration = FilterRegistrationBean(MyFilter())
        // ...
        registration.setDispatcherTypes(EnumSet.allOf(DispatcherType::class.java))
        return registration
    }

}

Note that the default FilterRegistrationBean does not include the ERROR dispatcher type.

Error Handling in a WAR Deployment

When deployed to a servlet container, Spring Boot uses its error page filter to forward a request with an error status to the appropriate error page. This is necessary as the servlet specification does not provide an API for registering error pages. Depending on the container that you are deploying your war file to and the technologies that your application uses, some additional configuration may be required.

The error page filter can only forward the request to the correct error page if the response has not already been committed. By default, WebSphere Application Server 8.0 and later commits the response upon successful completion of a servlet’s service method. You should disable this behavior by setting com.ibm.ws.webcontainer.invokeFlushAfterService to false.

If you are using Spring Security and want to access the principal in an error page, you must configure Spring Security’s filter to be invoked on error dispatches. To do so, set the spring.security.filter.dispatcher-types property to async, error, forward, request.

CORS Support

Cross-origin resource sharing (CORS) is a W3C specification implemented by most browsers that lets you specify in a flexible way what kind of cross-domain requests are authorized, instead of using some less secure and less powerful approaches such as IFRAME or JSONP.

As of version 4.2, Spring MVC supports CORS. Using controller method CORS configuration with @CrossOrigin annotations in your Spring Boot application does not require any specific configuration. Global CORS configuration can be defined by registering a WebMvcConfigurer bean with a customized addCorsMappings(CorsRegistry) method, as shown in the following example:

Java
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration(proxyBeanMethods = false)
public class MyCorsConfiguration {

    @Bean
    public WebMvcConfigurer corsConfigurer() {
        return new WebMvcConfigurer() {

            @Override
            public void addCorsMappings(CorsRegistry registry) {
                registry.addMapping("/api/**");
            }

        };
    }

}
Kotlin
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import org.springframework.web.servlet.config.annotation.CorsRegistry
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer

@Configuration(proxyBeanMethods = false)
class MyCorsConfiguration {

    @Bean
    fun corsConfigurer(): WebMvcConfigurer {
        return object : WebMvcConfigurer {
            override fun addCorsMappings(registry: CorsRegistry) {
                registry.addMapping("/api/**")
            }
        }
    }

}

8.1.2. JAX-RS and Jersey

If you prefer the JAX-RS programming model for REST endpoints, you can use one of the available implementations instead of Spring MVC. Jersey and Apache CXF work quite well out of the box. CXF requires you to register its Servlet or Filter as a @Bean in your application context. Jersey has some native Spring support, so we also provide auto-configuration support for it in Spring Boot, together with a starter.

To get started with Jersey, include the spring-boot-starter-jersey as a dependency and then you need one @Bean of type ResourceConfig in which you register all the endpoints, as shown in the following example:

Java
import org.glassfish.jersey.server.ResourceConfig;

import org.springframework.stereotype.Component;

@Component
public class MyJerseyConfig extends ResourceConfig {

    public MyJerseyConfig() {
        register(MyEndpoint.class);
    }

}
Kotlin
import org.glassfish.jersey.server.ResourceConfig
import org.springframework.stereotype.Component

@Component
class MyJerseyConfig : ResourceConfig() {

    init {
        register(MyEndpoint::class.java)
    }

}
Jersey’s support for scanning executable archives is rather limited. For example, it cannot scan for endpoints in a package found in a fully executable jar file or in WEB-INF/classes when running an executable war file. To avoid this limitation, the packages method should not be used, and endpoints should be registered individually by using the register method, as shown in the preceding example.

For more advanced customizations, you can also register an arbitrary number of beans that implement ResourceConfigCustomizer.

All the registered endpoints should be @Components with HTTP resource annotations (@GET and others), as shown in the following example:

Java
import javax.ws.rs.GET;
import javax.ws.rs.Path;

import org.springframework.stereotype.Component;

@Component
@Path("/hello")
public class MyEndpoint {

    @GET
    public String message() {
        return "Hello";
    }

}
Kotlin
import org.springframework.stereotype.Component
import javax.ws.rs.GET
import javax.ws.rs.Path

@Component
@Path("/hello")
class MyEndpoint {

    @GET
    fun message(): String {
        return "Hello"
    }

}

Since the Endpoint is a Spring @Component, its lifecycle is managed by Spring and you can use the @Autowired annotation to inject dependencies and use the @Value annotation to inject external configuration. By default, the Jersey servlet is registered and mapped to /*. You can change the mapping by adding @ApplicationPath to your ResourceConfig.

By default, Jersey is set up as a servlet in a @Bean of type ServletRegistrationBean named jerseyServletRegistration. By default, the servlet is initialized lazily, but you can customize that behavior by setting spring.jersey.servlet.load-on-startup. You can disable or override that bean by creating one of your own with the same name. You can also use a filter instead of a servlet by setting spring.jersey.type=filter (in which case, the @Bean to replace or override is jerseyFilterRegistration). The filter has an @Order, which you can set with spring.jersey.filter.order. When using Jersey as a filter, a servlet that will handle any requests that are not intercepted by Jersey must be present. If your application does not contain such a servlet, you may want to enable the default servlet by setting server.servlet.register-default-servlet to true. Both the servlet and the filter registrations can be given init parameters by using spring.jersey.init.* to specify a map of properties.

8.1.3. Embedded Servlet Container Support

For servlet application, Spring Boot includes support for embedded Tomcat, Jetty, and Undertow servers. Most developers use the appropriate “Starter” to obtain a fully configured instance. By default, the embedded server listens for HTTP requests on port 8080.

Servlets, Filters, and Listeners

When using an embedded servlet container, you can register servlets, filters, and all the listeners (such as HttpSessionListener) from the servlet spec, either by using Spring beans or by scanning for servlet components.

Registering Servlets, Filters, and Listeners as Spring Beans

Any Servlet, Filter, or servlet *Listener instance that is a Spring bean is registered with the embedded container. This can be particularly convenient if you want to refer to a value from your application.properties during configuration.

By default, if the context contains only a single Servlet, it is mapped to /. In the case of multiple servlet beans, the bean name is used as a path prefix. Filters map to /*.

If convention-based mapping is not flexible enough, you can use the ServletRegistrationBean, FilterRegistrationBean, and ServletListenerRegistrationBean classes for complete control.

It is usually safe to leave filter beans unordered. If a specific order is required, you should annotate the Filter with @Order or make it implement Ordered. You cannot configure the order of a Filter by annotating its bean method with @Order. If you cannot change the Filter class to add @Order or implement Ordered, you must define a FilterRegistrationBean for the Filter and set the registration bean’s order using the setOrder(int) method. Avoid configuring a filter that reads the request body at Ordered.HIGHEST_PRECEDENCE, since it might go against the character encoding configuration of your application. If a servlet filter wraps the request, it should be configured with an order that is less than or equal to OrderedFilter.REQUEST_WRAPPER_FILTER_MAX_ORDER.

To see the order of every Filter in your application, enable debug level logging for the web logging group (logging.level.web=debug). Details of the registered filters, including their order and URL patterns, will then be logged at startup.
Take care when registering Filter beans since they are initialized very early in the application lifecycle. If you need to register a Filter that interacts with other beans, consider using a DelegatingFilterProxyRegistrationBean instead.
Servlet Context Initialization

Embedded servlet containers do not directly execute the servlet 3.0+ javax.servlet.ServletContainerInitializer interface or Spring’s org.springframework.web.WebApplicationInitializer interface. This is an intentional design decision intended to reduce the risk that third party libraries designed to run inside a war may break Spring Boot applications.

If you need to perform servlet context initialization in a Spring Boot application, you should register a bean that implements the org.springframework.boot.web.servlet.ServletContextInitializer interface. The single onStartup method provides access to the ServletContext and, if necessary, can easily be used as an adapter to an existing WebApplicationInitializer.

Scanning for Servlets, Filters, and listeners

When using an embedded container, automatic registration of classes annotated with @WebServlet, @WebFilter, and @WebListener can be enabled by using @ServletComponentScan.

@ServletComponentScan has no effect in a standalone container, where the container’s built-in discovery mechanisms are used instead.
The ServletWebServerApplicationContext

Under the hood, Spring Boot uses a different type of ApplicationContext for embedded servlet container support. The ServletWebServerApplicationContext is a special type of WebApplicationContext that bootstraps itself by searching for a single ServletWebServerFactory bean. Usually a TomcatServletWebServerFactory, JettyServletWebServerFactory, or UndertowServletWebServerFactory has been auto-configured.

You usually do not need to be aware of these implementation classes. Most applications are auto-configured, and the appropriate ApplicationContext and ServletWebServerFactory are created on your behalf.

In an embedded container setup, the ServletContext is set as part of server startup which happens during application context initialization. Because of this beans in the ApplicationContext cannot be reliably initialized with a ServletContext. One way to get around this is to inject ApplicationContext as a dependency of the bean and access the ServletContext only when it is needed. Another way is to use a callback once the server has started. This can be done using an ApplicationListener which listens for the ApplicationStartedEvent as follows:

import javax.servlet.ServletContext;

import org.springframework.boot.context.event.ApplicationStartedEvent;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationListener;
import org.springframework.web.context.WebApplicationContext;

public class MyDemoBean implements ApplicationListener<ApplicationStartedEvent> {

    private ServletContext servletContext;

    @Override
    public void onApplicationEvent(ApplicationStartedEvent event) {
        ApplicationContext applicationContext = event.getApplicationContext();
        this.servletContext = ((WebApplicationContext) applicationContext).getServletContext();
    }

}
Customizing Embedded Servlet Containers

Common servlet container settings can be configured by using Spring Environment properties. Usually, you would define the properties in your application.properties or application.yaml file.

Common server settings include:

  • Network settings: Listen port for incoming HTTP requests (server.port), interface address to bind to server.address, and so on.

  • Session settings: Whether the session is persistent (server.servlet.session.persistent), session timeout (server.servlet.session.timeout), location of session data (server.servlet.session.store-dir), and session-cookie configuration (server.servlet.session.cookie.*).

  • Error management: Location of the error page (server.error.path) and so on.

  • SSL

  • HTTP compression

Spring Boot tries as much as possible to expose common settings, but this is not always possible. For those cases, dedicated namespaces offer server-specific customizations (see server.tomcat and server.undertow). For instance, access logs can be configured with specific features of the embedded servlet container.

See the ServerProperties class for a complete list.
SameSite Cookies

The SameSite cookie attribute can be used by web browsers to control if and how cookies are submitted in cross-site requests. The attribute is particularly relevant for modern web browsers which have started to change the default value that is used when the attribute is missing.

If you want to change the SameSite attribute of your session cookie, you can use the server.servlet.session.cookie.same-site property. This property is supported by auto-configured Tomcat, Jetty and Undertow servers. It is also used to configure Spring Session servlet based SessionRepository beans.

For example, if you want your session cookie to have a SameSite attribute of None, you can add the following to your application.properties or application.yaml file:

Properties
server.servlet.session.cookie.same-site=none
Yaml
server:
  servlet:
    session:
      cookie:
        same-site: "none"

If you want to change the SameSite attribute on other cookies added to your HttpServletResponse, you can use a CookieSameSiteSupplier. The CookieSameSiteSupplier is passed a Cookie and may return a SameSite value, or null.

There are a number of convenience factory and filter methods that you can use to quickly match specific cookies. For example, adding the following bean will automatically apply a SameSite of Lax for all cookies with a name that matches the regular expression myapp.*.

Java
import org.springframework.boot.web.servlet.server.CookieSameSiteSupplier;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration(proxyBeanMethods = false)
public class MySameSiteConfiguration {

    @Bean
    public CookieSameSiteSupplier applicationCookieSameSiteSupplier() {
        return CookieSameSiteSupplier.ofLax().whenHasNameMatching("myapp.*");
    }

}
Kotlin
import org.springframework.boot.web.servlet.server.CookieSameSiteSupplier
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration

@Configuration(proxyBeanMethods = false)
class MySameSiteConfiguration {

    @Bean
    fun applicationCookieSameSiteSupplier(): CookieSameSiteSupplier {
        return CookieSameSiteSupplier.ofLax().whenHasNameMatching("myapp.*")
    }

}
Character Encoding

The character encoding behavior of the embedded servlet container for request and response handling can be configured using the server.servlet.encoding.* configuration properties.

When a request’s Accept-Language header indicates a locale for the request it will be automatically mapped to a charset by the servlet container. Each containers providers default locale to charset mappings and you should verify that they meet your application’s needs. When they do not, use the server.servlet.encoding.mapping configuration property to customize the mappings, as shown in the following example:

Properties
server.servlet.encoding.mapping.ko=UTF-8
Yaml
server:
  servlet:
    encoding:
      mapping:
        ko: "UTF-8"

In the preceding example, the ko (Korean) locale has been mapped to UTF-8. This is equivalent to a <locale-encoding-mapping-list> entry in a web.xml file of a traditional war deployment.

Programmatic Customization

If you need to programmatically configure your embedded servlet container, you can register a Spring bean that implements the WebServerFactoryCustomizer interface. WebServerFactoryCustomizer provides access to the ConfigurableServletWebServerFactory, which includes numerous customization setter methods. The following example shows programmatically setting the port:

Java
import org.springframework.boot.web.server.WebServerFactoryCustomizer;
import org.springframework.boot.web.servlet.server.ConfigurableServletWebServerFactory;
import org.springframework.stereotype.Component;

@Component
public class MyWebServerFactoryCustomizer implements WebServerFactoryCustomizer<ConfigurableServletWebServerFactory> {

    @Override
    public void customize(ConfigurableServletWebServerFactory server) {
        server.setPort(9000);
    }

}
Kotlin
import org.springframework.boot.web.server.WebServerFactoryCustomizer
import org.springframework.boot.web.servlet.server.ConfigurableServletWebServerFactory
import org.springframework.stereotype.Component

@Component
class MyWebServerFactoryCustomizer : WebServerFactoryCustomizer<ConfigurableServletWebServerFactory> {

    override fun customize(server: ConfigurableServletWebServerFactory) {
        server.setPort(9000)
    }

}

TomcatServletWebServerFactory, JettyServletWebServerFactory and UndertowServletWebServerFactory are dedicated variants of ConfigurableServletWebServerFactory that have additional customization setter methods for Tomcat, Jetty and Undertow respectively. The following example shows how to customize TomcatServletWebServerFactory that provides access to Tomcat-specific configuration options:

Java
import java.time.Duration;

import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory;
import org.springframework.boot.web.server.WebServerFactoryCustomizer;
import org.springframework.stereotype.Component;

@Component
public class MyTomcatWebServerFactoryCustomizer implements WebServerFactoryCustomizer<TomcatServletWebServerFactory> {

    @Override
    public void customize(TomcatServletWebServerFactory server) {
        server.addConnectorCustomizers((connector) -> connector.setAsyncTimeout(Duration.ofSeconds(20).toMillis()));
    }

}
Kotlin
import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory
import org.springframework.boot.web.server.WebServerFactoryCustomizer
import org.springframework.stereotype.Component
import java.time.Duration

@Component
class MyTomcatWebServerFactoryCustomizer : WebServerFactoryCustomizer<TomcatServletWebServerFactory> {

    override fun customize(server: TomcatServletWebServerFactory) {
        server.addConnectorCustomizers({ connector -> connector.asyncTimeout = Duration.ofSeconds(20).toMillis() })
    }

}
Customizing ConfigurableServletWebServerFactory Directly

For more advanced use cases that require you to extend from ServletWebServerFactory, you can expose a bean of such type yourself.

Setters are provided for many configuration options. Several protected method “hooks” are also provided should you need to do something more exotic. See the source code documentation for details.

Auto-configured customizers are still applied on your custom factory, so use that option carefully.
JSP Limitations

When running a Spring Boot application that uses an embedded servlet container (and is packaged as an executable archive), there are some limitations in the JSP support.

  • With Jetty and Tomcat, it should work if you use war packaging. An executable war will work when launched with java -jar, and will also be deployable to any standard container. JSPs are not supported when using an executable jar.

  • Undertow does not support JSPs.

  • Creating a custom error.jsp page does not override the default view for error handling. Custom error pages should be used instead.

8.2. Reactive Web Applications

Spring Boot simplifies development of reactive web applications by providing auto-configuration for Spring Webflux.

8.2.1. The “Spring WebFlux Framework”

Spring WebFlux is the new reactive web framework introduced in Spring Framework 5.0. Unlike Spring MVC, it does not require the servlet API, is fully asynchronous and non-blocking, and implements the Reactive Streams specification through the Reactor project.

Spring WebFlux comes in two flavors: functional and annotation-based. The annotation-based one is quite close to the Spring MVC model, as shown in the following example:

Java
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/users")
public class MyRestController {

    private final UserRepository userRepository;

    private final CustomerRepository customerRepository;

    public MyRestController(UserRepository userRepository, CustomerRepository customerRepository) {
        this.userRepository = userRepository;
        this.customerRepository = customerRepository;
    }

    @GetMapping("/{userId}")
    public Mono<User> getUser(@PathVariable Long userId) {
        return this.userRepository.findById(userId);
    }

    @GetMapping("/{userId}/customers")
    public Flux<Customer> getUserCustomers(@PathVariable Long userId) {
        return this.userRepository.findById(userId).flatMapMany(this.customerRepository::findByUser);
    }

    @DeleteMapping("/{userId}")
    public Mono<Void> deleteUser(@PathVariable Long userId) {
        return this.userRepository.deleteById(userId);
    }

}
Kotlin
import org.springframework.web.bind.annotation.DeleteMapping
import org.springframework.web.bind.annotation.GetMapping
import org.springframework.web.bind.annotation.PathVariable
import org.springframework.web.bind.annotation.RequestMapping
import org.springframework.web.bind.annotation.RestController
import reactor.core.publisher.Flux
import reactor.core.publisher.Mono

@RestController
@RequestMapping("/users")
class MyRestController(private val userRepository: UserRepository, private val customerRepository: CustomerRepository) {

    @GetMapping("/{userId}")
    fun getUser(@PathVariable userId: Long): Mono<User?> {
        return userRepository.findById(userId)
    }

    @GetMapping("/{userId}/customers")
    fun getUserCustomers(@PathVariable userId: Long): Flux<Customer> {
        return userRepository.findById(userId).flatMapMany { user: User? ->
            customerRepository.findByUser(user)
        }
    }

    @DeleteMapping("/{userId}")
    fun deleteUser(@PathVariable userId: Long): Mono<Void> {
        return userRepository.deleteById(userId)
    }

}

“WebFlux.fn”, the functional variant, separates the routing configuration from the actual handling of the requests, as shown in the following example:

Java
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.MediaType;
import org.springframework.web.reactive.function.server.RequestPredicate;
import org.springframework.web.reactive.function.server.RouterFunction;
import org.springframework.web.reactive.function.server.ServerResponse;

import static org.springframework.web.reactive.function.server.RequestPredicates.accept;
import static org.springframework.web.reactive.function.server.RouterFunctions.route;

@Configuration(proxyBeanMethods = false)
public class MyRoutingConfiguration {

    private static final RequestPredicate ACCEPT_JSON = accept(MediaType.APPLICATION_JSON);

    @Bean
    public RouterFunction<ServerResponse> monoRouterFunction(MyUserHandler userHandler) {
        return route()
                .GET("/{user}", ACCEPT_JSON, userHandler::getUser)
                .GET("/{user}/customers", ACCEPT_JSON, userHandler::getUserCustomers)
                .DELETE("/{user}", ACCEPT_JSON, userHandler::deleteUser)
                .build();
    }

}
Kotlin
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import org.springframework.http.MediaType
import org.springframework.web.reactive.function.server.RequestPredicates.DELETE
import org.springframework.web.reactive.function.server.RequestPredicates.GET
import org.springframework.web.reactive.function.server.RequestPredicates.accept
import org.springframework.web.reactive.function.server.RouterFunction
import org.springframework.web.reactive.function.server.RouterFunctions
import org.springframework.web.reactive.function.server.ServerResponse

@Configuration(proxyBeanMethods = false)
class MyRoutingConfiguration {

    @Bean
    fun monoRouterFunction(userHandler: MyUserHandler): RouterFunction<ServerResponse> {
        return RouterFunctions.route(
            GET("/{user}").and(ACCEPT_JSON), userHandler::getUser).andRoute(
            GET("/{user}/customers").and(ACCEPT_JSON), userHandler::getUserCustomers).andRoute(
            DELETE("/{user}").and(ACCEPT_JSON), userHandler::deleteUser)
    }

    companion object {
        private val ACCEPT_JSON = accept(MediaType.APPLICATION_JSON)
    }

}
Java
import reactor.core.publisher.Mono;

import org.springframework.stereotype.Component;
import org.springframework.web.reactive.function.server.ServerRequest;
import org.springframework.web.reactive.function.server.ServerResponse;

@Component
public class MyUserHandler {

    public Mono<ServerResponse> getUser(ServerRequest request) {
        ...
    }

    public Mono<ServerResponse> getUserCustomers(ServerRequest request) {
        ...
    }

    public Mono<ServerResponse> deleteUser(ServerRequest request) {
        ...
    }

}
Kotlin
import org.springframework.stereotype.Component
import org.springframework.web.reactive.function.server.ServerRequest
import org.springframework.web.reactive.function.server.ServerResponse
import reactor.core.publisher.Mono

@Component
class MyUserHandler {

    fun getUser(request: ServerRequest?): Mono<ServerResponse> {
        return ServerResponse.ok().build()
    }

    fun getUserCustomers(request: ServerRequest?): Mono<ServerResponse> {
        return ServerResponse.ok().build()
    }

    fun deleteUser(request: ServerRequest?): Mono<ServerResponse> {
        return ServerResponse.ok().build()
    }

}

WebFlux is part of the Spring Framework and detailed information is available in its reference documentation.

You can define as many RouterFunction beans as you like to modularize the definition of the router. Beans can be ordered if you need to apply a precedence.

To get started, add the spring-boot-starter-webflux module to your application.

Adding both spring-boot-starter-web and spring-boot-starter-webflux modules in your application results in Spring Boot auto-configuring Spring MVC, not WebFlux. This behavior has been chosen because many Spring developers add spring-boot-starter-webflux to their Spring MVC application to use the reactive WebClient. You can still enforce your choice by setting the chosen application type to SpringApplication.setWebApplicationType(WebApplicationType.REACTIVE).
Spring WebFlux Auto-configuration

Spring Boot provides auto-configuration for Spring WebFlux that works well with most applications.

The auto-configuration adds the following features on top of Spring’s defaults:

If you want to keep Spring Boot WebFlux features and you want to add additional WebFlux configuration, you can add your own @Configuration class of type WebFluxConfigurer but without @EnableWebFlux.

If you want to take complete control of Spring WebFlux, you can add your own @Configuration annotated with @EnableWebFlux.

Spring WebFlux Conversion Service

If you want to customize the ConversionService used by Spring WebFlux, you can provide a WebFluxConfigurer bean with an addFormatters method.

Conversion can also be customized using the spring.webflux.format.* configuration properties. When not configured, the following defaults are used:

Property DateTimeFormatter

spring.webflux.format.date

ofLocalizedDate(FormatStyle.SHORT)

spring.webflux.format.time

ofLocalizedTime(FormatStyle.SHORT)

spring.webflux.format.date-time

ofLocalizedDateTime(FormatStyle.SHORT)

HTTP Codecs with HttpMessageReaders and HttpMessageWriters

Spring WebFlux uses the HttpMessageReader and HttpMessageWriter interfaces to convert HTTP requests and responses. They are configured with CodecConfigurer to have sensible defaults by looking at the libraries available in your classpath.

Spring Boot provides dedicated configuration properties for codecs, spring.codec.*. It also applies further customization by using CodecCustomizer instances. For example, spring.jackson.* configuration keys are applied to the Jackson codec.

If you need to add or customize codecs, you can create a custom CodecCustomizer component, as shown in the following example:

Java
import org.springframework.boot.web.codec.CodecCustomizer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.codec.ServerSentEventHttpMessageReader;

@Configuration(proxyBeanMethods = false)
public class MyCodecsConfiguration {

    @Bean
    public CodecCustomizer myCodecCustomizer() {
        return (configurer) -> {
            configurer.registerDefaults(false);
            configurer.customCodecs().register(new ServerSentEventHttpMessageReader());
            // ...
        };
    }

}
Kotlin
import org.springframework.boot.web.codec.CodecCustomizer
import org.springframework.context.annotation.Bean
import org.springframework.http.codec.CodecConfigurer
import org.springframework.http.codec.ServerSentEventHttpMessageReader

class MyCodecsConfiguration {

    @Bean
    fun myCodecCustomizer(): CodecCustomizer {
        return CodecCustomizer { configurer: CodecConfigurer ->
            configurer.registerDefaults(false)
            configurer.customCodecs().register(ServerSentEventHttpMessageReader())
        }
    }

}
Static Content

By default, Spring Boot serves static content from a directory called /static (or /public or /resources or /META-INF/resources) in the classpath. It uses the ResourceWebHandler from Spring WebFlux so that you can modify that behavior by adding your own WebFluxConfigurer and overriding the addResourceHandlers method.

By default, resources are mapped on /**, but you can tune that by setting the spring.webflux.static-path-pattern property. For instance, relocating all resources to /resources/** can be achieved as follows:

Properties
spring.webflux.static-path-pattern=/resources/**
Yaml
spring:
  webflux:
    static-path-pattern: "/resources/**"

You can also customize the static resource locations by using spring.web.resources.static-locations. Doing so replaces the default values with a list of directory locations. If you do so, the default welcome page detection switches to your custom locations. So, if there is an index.html in any of your locations on startup, it is the home page of the application.

In addition to the “standard” static resource locations listed earlier, a special case is made for Webjars content. Any resources with a path in /webjars/** are served from jar files if they are packaged in the Webjars format.

Spring WebFlux applications do not strictly depend on the servlet API, so they cannot be deployed as war files and do not use the src/main/webapp directory.
Welcome Page

Spring Boot supports both static and templated welcome pages. It first looks for an index.html file in the configured static content locations. If one is not found, it then looks for an index template. If either is found, it is automatically used as the welcome page of the application.

Template Engines

As well as REST web services, you can also use Spring WebFlux to serve dynamic HTML content. Spring WebFlux supports a variety of templating technologies, including Thymeleaf, FreeMarker, and Mustache.

Spring Boot includes auto-configuration support for the following templating engines:

When you use one of these templating engines with the default configuration, your templates are picked up automatically from src/main/resources/templates.

Error Handling

Spring Boot provides a WebExceptionHandler that handles all errors in a sensible way. Its position in the processing order is immediately before the handlers provided by WebFlux, which are considered last. For machine clients, it produces a JSON response with details of the error, the HTTP status, and the exception message. For browser clients, there is a “whitelabel” error handler that renders the same data in HTML format. You can also provide your own HTML templates to display errors (see the next section).

The first step to customizing this feature often involves using the existing mechanism but replacing or augmenting the error contents. For that, you can add a bean of type ErrorAttributes.

To change the error handling behavior, you can implement ErrorWebExceptionHandler and register a bean definition of that type. Because an ErrorWebExceptionHandler is quite low-level, Spring Boot also provides a convenient AbstractErrorWebExceptionHandler to let you handle errors in a WebFlux functional way, as shown in the following example:

Java
import reactor.core.publisher.Mono;

import org.springframework.boot.autoconfigure.web.WebProperties;
import org.springframework.boot.autoconfigure.web.reactive.error.AbstractErrorWebExceptionHandler;
import org.springframework.boot.web.reactive.error.ErrorAttributes;
import org.springframework.context.ApplicationContext;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.codec.ServerCodecConfigurer;
import org.springframework.stereotype.Component;
import org.springframework.web.reactive.function.server.RouterFunction;
import org.springframework.web.reactive.function.server.RouterFunctions;
import org.springframework.web.reactive.function.server.ServerRequest;
import org.springframework.web.reactive.function.server.ServerResponse;
import org.springframework.web.reactive.function.server.ServerResponse.BodyBuilder;

@Component
public class MyErrorWebExceptionHandler extends AbstractErrorWebExceptionHandler {

    public MyErrorWebExceptionHandler(ErrorAttributes errorAttributes, WebProperties webProperties,
            ApplicationContext applicationContext, ServerCodecConfigurer serverCodecConfigurer) {
        super(errorAttributes, webProperties.getResources(), applicationContext);
        setMessageReaders(serverCodecConfigurer.getReaders());
        setMessageWriters(serverCodecConfigurer.getWriters());
    }

    @Override
    protected RouterFunction<ServerResponse> getRoutingFunction(ErrorAttributes errorAttributes) {
        return RouterFunctions.route(this::acceptsXml, this::handleErrorAsXml);
    }

    private boolean acceptsXml(ServerRequest request) {
        return request.headers().accept().contains(MediaType.APPLICATION_XML);
    }

    public Mono<ServerResponse> handleErrorAsXml(ServerRequest request) {
        BodyBuilder builder = ServerResponse.status(HttpStatus.INTERNAL_SERVER_ERROR);
        // ... additional builder calls
        return builder.build();
    }

}
Kotlin
import org.springframework.boot.autoconfigure.web.WebProperties
import org.springframework.boot.autoconfigure.web.reactive.error.AbstractErrorWebExceptionHandler
import org.springframework.boot.web.reactive.error.ErrorAttributes
import org.springframework.context.ApplicationContext
import org.springframework.http.HttpStatus
import org.springframework.http.MediaType
import org.springframework.http.codec.ServerCodecConfigurer
import org.springframework.stereotype.Component
import org.springframework.web.reactive.function.server.RouterFunction
import org.springframework.web.reactive.function.server.RouterFunctions
import org.springframework.web.reactive.function.server.ServerRequest
import org.springframework.web.reactive.function.server.ServerResponse
import reactor.core.publisher.Mono

@Component
class MyErrorWebExceptionHandler(
        errorAttributes: ErrorAttributes, webProperties: WebProperties,
        applicationContext: ApplicationContext, serverCodecConfigurer: ServerCodecConfigurer
) : AbstractErrorWebExceptionHandler(errorAttributes, webProperties.resources, applicationContext) {

    init {
        setMessageReaders(serverCodecConfigurer.readers)
        setMessageWriters(serverCodecConfigurer.writers)
    }

    override fun getRoutingFunction(errorAttributes: ErrorAttributes): RouterFunction<ServerResponse> {
        return RouterFunctions.route(this::acceptsXml, this::handleErrorAsXml)
    }

    private fun acceptsXml(request: ServerRequest): Boolean {
        return request.headers().accept().contains(MediaType.APPLICATION_XML)
    }

    fun handleErrorAsXml(request: ServerRequest): Mono<ServerResponse> {
        val builder = ServerResponse.status(HttpStatus.INTERNAL_SERVER_ERROR)
        // ... additional builder calls
        return builder.build()
    }

}

For a more complete picture, you can also subclass DefaultErrorWebExceptionHandler directly and override specific methods.

In some cases, errors handled at the controller or handler function level are not recorded by the metrics infrastructure. Applications can ensure that such exceptions are recorded with the request metrics by setting the handled exception as a request attribute:

Java
import org.springframework.boot.web.reactive.error.ErrorAttributes;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.reactive.result.view.Rendering;
import org.springframework.web.server.ServerWebExchange;

@Controller
public class MyExceptionHandlingController {

    @GetMapping("/profile")
    public Rendering userProfile() {
        // ...
        throw new IllegalStateException();
    }

    @ExceptionHandler(IllegalStateException.class)
    public Rendering handleIllegalState(ServerWebExchange exchange, IllegalStateException exc) {
        exchange.getAttributes().putIfAbsent(ErrorAttributes.ERROR_ATTRIBUTE, exc);
        return Rendering.view("errorView").modelAttribute("message", exc.getMessage()).build();
    }

}
Kotlin
import org.springframework.boot.web.reactive.error.ErrorAttributes
import org.springframework.stereotype.Controller
import org.springframework.web.bind.annotation.ExceptionHandler
import org.springframework.web.bind.annotation.GetMapping
import org.springframework.web.reactive.result.view.Rendering
import org.springframework.web.server.ServerWebExchange

@Controller
class MyExceptionHandlingController {

    @GetMapping("/profile")
    fun userProfile(): Rendering {
        // ...
        throw IllegalStateException()
    }

    @ExceptionHandler(IllegalStateException::class)
    fun handleIllegalState(exchange: ServerWebExchange, exc: IllegalStateException): Rendering {
        exchange.attributes.putIfAbsent(ErrorAttributes.ERROR_ATTRIBUTE, exc)
        return Rendering.view("errorView").modelAttribute("message", exc.message ?: "").build()
    }

}
Custom Error Pages

If you want to display a custom HTML error page for a given status code, you can add views that resolve from error/*, for example by adding files to a /error directory. Error pages can either be static HTML (that is, added under any of the static resource directories) or built with templates. The name of the file should be the exact status code, a status code series mask, or error for a default if nothing else matches. Note that the path to the default error view is error/error, whereas with Spring MVC the default error view is error.

For example, to map 404 to a static HTML file, your directory structure would be as follows:

src/
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- public/
             +- error/
             |   +- 404.html
             +- <other public assets>

To map all 5xx errors by using a Mustache template, your directory structure would be as follows:

src/
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- templates/
             +- error/
             |   +- 5xx.mustache
             +- <other templates>
Web Filters

Spring WebFlux provides a WebFilter interface that can be implemented to filter HTTP request-response exchanges. WebFilter beans found in the application context will be automatically used to filter each exchange.

Where the order of the filters is important they can implement Ordered or be annotated with @Order. Spring Boot auto-configuration may configure web filters for you. When it does so, the orders shown in the following table will be used:

Web Filter Order

MetricsWebFilter

Ordered.HIGHEST_PRECEDENCE + 1

WebFilterChainProxy (Spring Security)

-100

HttpTraceWebFilter

Ordered.LOWEST_PRECEDENCE - 10

8.2.2. Embedded Reactive Server Support

Spring Boot includes support for the following embedded reactive web servers: Reactor Netty, Tomcat, Jetty, and Undertow. Most developers use the appropriate “Starter” to obtain a fully configured instance. By default, the embedded server listens for HTTP requests on port 8080.

Customizing Reactive Servers

Common reactive web server settings can be configured by using Spring Environment properties. Usually, you would define the properties in your application.properties or application.yaml file.

Common server settings include:

  • Network settings: Listen port for incoming HTTP requests (server.port), interface address to bind to server.address, and so on.

  • Error management: Location of the error page (server.error.path) and so on.

  • SSL

  • HTTP compression

Spring Boot tries as much as possible to expose common settings, but this is not always possible. For those cases, dedicated namespaces such as server.netty.* offer server-specific customizations.

See the ServerProperties class for a complete list.
Programmatic Customization

If you need to programmatically configure your reactive web server, you can register a Spring bean that implements the WebServerFactoryCustomizer interface. WebServerFactoryCustomizer provides access to the ConfigurableReactiveWebServerFactory, which includes numerous customization setter methods. The following example shows programmatically setting the port:

Java
import org.springframework.boot.web.reactive.server.ConfigurableReactiveWebServerFactory;
import org.springframework.boot.web.server.WebServerFactoryCustomizer;
import org.springframework.stereotype.Component;

@Component
public class MyWebServerFactoryCustomizer implements WebServerFactoryCustomizer<ConfigurableReactiveWebServerFactory> {

    @Override
    public void customize(ConfigurableReactiveWebServerFactory server) {
        server.setPort(9000);
    }

}
Kotlin
import org.springframework.boot.web.server.WebServerFactoryCustomizer
import org.springframework.boot.web.reactive.server.ConfigurableReactiveWebServerFactory
import org.springframework.stereotype.Component

@Component
class MyWebServerFactoryCustomizer : WebServerFactoryCustomizer<ConfigurableReactiveWebServerFactory> {

    override fun customize(server: ConfigurableReactiveWebServerFactory) {
        server.setPort(9000)
    }

}

JettyReactiveWebServerFactory, NettyReactiveWebServerFactory, TomcatReactiveWebServerFactory, and UndertowServletWebServerFactory are dedicated variants of ConfigurableReactiveWebServerFactory that have additional customization setter methods for Jetty, Reactor Netty, Tomcat, and Undertow respectively. The following example shows how to customize NettyReactiveWebServerFactory that provides access to Reactor Netty-specific configuration options:

Java
import java.time.Duration;

import org.springframework.boot.web.embedded.netty.NettyReactiveWebServerFactory;
import org.springframework.boot.web.server.WebServerFactoryCustomizer;
import org.springframework.stereotype.Component;

@Component
public class MyNettyWebServerFactoryCustomizer implements WebServerFactoryCustomizer<NettyReactiveWebServerFactory> {

    @Override
    public void customize(NettyReactiveWebServerFactory factory) {
        factory.addServerCustomizers((server) -> server.idleTimeout(Duration.ofSeconds(20)));
    }

}
Kotlin
import org.springframework.boot.web.embedded.netty.NettyReactiveWebServerFactory
import org.springframework.boot.web.server.WebServerFactoryCustomizer
import org.springframework.stereotype.Component
import java.time.Duration

@Component
class MyNettyWebServerFactoryCustomizer : WebServerFactoryCustomizer<NettyReactiveWebServerFactory> {

    override fun customize(factory: NettyReactiveWebServerFactory) {
        factory.addServerCustomizers({ server -> server.idleTimeout(Duration.ofSeconds(20)) })
    }

}
Customizing ConfigurableReactiveWebServerFactory Directly

For more advanced use cases that require you to extend from ReactiveWebServerFactory, you can expose a bean of such type yourself.

Setters are provided for many configuration options. Several protected method “hooks” are also provided should you need to do something more exotic. See the source code documentation for details.

Auto-configured customizers are still applied on your custom factory, so use that option carefully.

8.2.3. Reactive Server Resources Configuration

When auto-configuring a Reactor Netty or Jetty server, Spring Boot will create specific beans that will provide HTTP resources to the server instance: ReactorResourceFactory or JettyResourceFactory.

By default, those resources will be also shared with the Reactor Netty and Jetty clients for optimal performances, given:

  • the same technology is used for server and client

  • the client instance is built using the WebClient.Builder bean auto-configured by Spring Boot

Developers can override the resource configuration for Jetty and Reactor Netty by providing a custom ReactorResourceFactory or JettyResourceFactory bean - this will be applied to both clients and servers.

You can learn more about the resource configuration on the client side in the WebClient Runtime section.

8.3. Graceful Shutdown

Graceful shutdown is supported with all four embedded web servers (Jetty, Reactor Netty, Tomcat, and Undertow) and with both reactive and servlet-based web applications. It occurs as part of closing the application context and is performed in the earliest phase of stopping SmartLifecycle beans. This stop processing uses a timeout which provides a grace period during which existing requests will be allowed to complete but no new requests will be permitted. The exact way in which new requests are not permitted varies depending on the web server that is being used. Jetty, Reactor Netty, and Tomcat will stop accepting requests at the network layer. Undertow will accept requests but respond immediately with a service unavailable (503) response.

Graceful shutdown with Tomcat requires Tomcat 9.0.33 or later.

To enable graceful shutdown, configure the server.shutdown property, as shown in the following example:

Properties
server.shutdown=graceful
Yaml
server:
  shutdown: "graceful"

To configure the timeout period, configure the spring.lifecycle.timeout-per-shutdown-phase property, as shown in the following example:

Properties
spring.lifecycle.timeout-per-shutdown-phase=20s
Yaml
spring:
  lifecycle:
    timeout-per-shutdown-phase: "20s"
Using graceful shutdown with your IDE may not work properly if it does not send a proper SIGTERM signal. See the documentation of your IDE for more details.

8.4. Spring Security

If Spring Security is on the classpath, then web applications are secured by default. Spring Boot relies on Spring Security’s content-negotiation strategy to determine whether to use httpBasic or formLogin. To add method-level security to a web application, you can also add @EnableGlobalMethodSecurity with your desired settings. Additional information can be found in the Spring Security Reference Guide.

The default UserDetailsService has a single user. The user name is user, and the password is random and is printed at WARN level when the application starts, as shown in the following example:

Using generated security password: 78fa095d-3f4c-48b1-ad50-e24c31d5cf35

This generated password is for development use only. Your security configuration must be updated before running your application in production.
If you fine-tune your logging configuration, ensure that the org.springframework.boot.autoconfigure.security category is set to log WARN-level messages. Otherwise, the default password is not printed.

You can change the username and password by providing a spring.security.user.name and spring.security.user.password.

The basic features you get by default in a web application are:

  • A UserDetailsService (or ReactiveUserDetailsService in case of a WebFlux application) bean with in-memory store and a single user with a generated password (see SecurityProperties.User for the properties of the user).

  • Form-based login or HTTP Basic security (depending on the Accept header in the request) for the entire application (including actuator endpoints if actuator is on the classpath).

  • A DefaultAuthenticationEventPublisher for publishing authentication events.

You can provide a different AuthenticationEventPublisher by adding a bean for it.

8.4.1. MVC Security

The default security configuration is implemented in SecurityAutoConfiguration and UserDetailsServiceAutoConfiguration. SecurityAutoConfiguration imports SpringBootWebSecurityConfiguration for web security and UserDetailsServiceAutoConfiguration configures authentication, which is also relevant in non-web applications. To switch off the default web application security configuration completely or to combine multiple Spring Security components such as OAuth2 Client and Resource Server, add a bean of type SecurityFilterChain (doing so does not disable the UserDetailsService configuration or Actuator’s security).

To also switch off the UserDetailsService configuration, you can add a bean of type UserDetailsService, AuthenticationProvider, or AuthenticationManager.

Access rules can be overridden by adding a custom SecurityFilterChain or WebSecurityConfigurerAdapter bean. Spring Boot provides convenience methods that can be used to override access rules for actuator endpoints and static resources. EndpointRequest can be used to create a RequestMatcher that is based on the management.endpoints.web.base-path property. PathRequest can be used to create a RequestMatcher for resources in commonly used locations.

8.4.2. WebFlux Security

Similar to Spring MVC applications, you can secure your WebFlux applications by adding the spring-boot-starter-security dependency. The default security configuration is implemented in ReactiveSecurityAutoConfiguration and UserDetailsServiceAutoConfiguration. ReactiveSecurityAutoConfiguration imports WebFluxSecurityConfiguration for web security and UserDetailsServiceAutoConfiguration configures authentication, which is also relevant in non-web applications. To switch off the default web application security configuration completely, you can add a bean of type WebFilterChainProxy (doing so does not disable the UserDetailsService configuration or Actuator’s security).

To also switch off the UserDetailsService configuration, you can add a bean of type ReactiveUserDetailsService or ReactiveAuthenticationManager.

Access rules and the use of multiple Spring Security components such as OAuth 2 Client and Resource Server can be configured by adding a custom SecurityWebFilterChain bean. Spring Boot provides convenience methods that can be used to override access rules for actuator endpoints and static resources. EndpointRequest can be used to create a ServerWebExchangeMatcher that is based on the management.endpoints.web.base-path property.

PathRequest can be used to create a ServerWebExchangeMatcher for resources in commonly used locations.

For example, you can customize your security configuration by adding something like:

Java
import org.springframework.boot.autoconfigure.security.reactive.PathRequest;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.config.web.server.ServerHttpSecurity;
import org.springframework.security.web.server.SecurityWebFilterChain;

import static org.springframework.security.config.Customizer.withDefaults;

@Configuration(proxyBeanMethods = false)
public class MyWebFluxSecurityConfiguration {

    @Bean
    public SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
        http.authorizeExchange((exchange) -> {
            exchange.matchers(PathRequest.toStaticResources().atCommonLocations()).permitAll();
            exchange.pathMatchers("/foo", "/bar").authenticated();
        });
        http.formLogin(withDefaults());
        return http.build();
    }

}
Kotlin
import org.springframework.boot.autoconfigure.security.reactive.PathRequest
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import org.springframework.security.config.web.server.ServerHttpSecurity
import org.springframework.security.web.server.SecurityWebFilterChain

@Configuration(proxyBeanMethods = false)
class MyWebFluxSecurityConfiguration {

    @Bean
    fun springSecurityFilterChain(http: ServerHttpSecurity): SecurityWebFilterChain {
        http.authorizeExchange { spec ->
            spec.matchers(PathRequest.toStaticResources().atCommonLocations()).permitAll()
            spec.pathMatchers("/foo", "/bar").authenticated()
        }
        http.formLogin()
        return http.build()
    }

}

8.4.3. OAuth2

OAuth2 is a widely used authorization framework that is supported by Spring.

Client

If you have spring-security-oauth2-client on your classpath, you can take advantage of some auto-configuration to set up OAuth2/Open ID Connect clients. This configuration makes use of the properties under OAuth2ClientProperties. The same properties are applicable to both servlet and reactive applications.

You can register multiple OAuth2 clients and providers under the spring.security.oauth2.client prefix, as shown in the following example:

Properties
spring.security.oauth2.client.registration.my-client-1.client-id=abcd
spring.security.oauth2.client.registration.my-client-1.client-secret=password
spring.security.oauth2.client.registration.my-client-1.client-name=Client for user scope
spring.security.oauth2.client.registration.my-client-1.provider=my-oauth-provider
spring.security.oauth2.client.registration.my-client-1.scope=user
spring.security.oauth2.client.registration.my-client-1.redirect-uri=https://my-redirect-uri.com
spring.security.oauth2.client.registration.my-client-1.client-authentication-method=basic
spring.security.oauth2.client.registration.my-client-1.authorization-grant-type=authorization_code

spring.security.oauth2.client.registration.my-client-2.client-id=abcd
spring.security.oauth2.client.registration.my-client-2.client-secret=password
spring.security.oauth2.client.registration.my-client-2.client-name=Client for email scope
spring.security.oauth2.client.registration.my-client-2.provider=my-oauth-provider
spring.security.oauth2.client.registration.my-client-2.scope=email
spring.security.oauth2.client.registration.my-client-2.redirect-uri=https://my-redirect-uri.com
spring.security.oauth2.client.registration.my-client-2.client-authentication-method=basic
spring.security.oauth2.client.registration.my-client-2.authorization-grant-type=authorization_code

spring.security.oauth2.client.provider.my-oauth-provider.authorization-uri=https://my-auth-server/oauth/authorize
spring.security.oauth2.client.provider.my-oauth-provider.token-uri=https://my-auth-server/oauth/token
spring.security.oauth2.client.provider.my-oauth-provider.user-info-uri=https://my-auth-server/userinfo
spring.security.oauth2.client.provider.my-oauth-provider.user-info-authentication-method=header
spring.security.oauth2.client.provider.my-oauth-provider.jwk-set-uri=https://my-auth-server/token_keys
spring.security.oauth2.client.provider.my-oauth-provider.user-name-attribute=name
Yaml
spring:
  security:
    oauth2:
      client:
        registration:
          my-client-1:
            client-id: "abcd"
            client-secret: "password"
            client-name: "Client for user scope"
            provider: "my-oauth-provider"
            scope: "user"
            redirect-uri: "https://my-redirect-uri.com"
            client-authentication-method: "basic"
            authorization-grant-type: "authorization_code"

          my-client-2:
            client-id: "abcd"
            client-secret: "password"
            client-name: "Client for email scope"
            provider: "my-oauth-provider"
            scope: "email"
            redirect-uri: "https://my-redirect-uri.com"
            client-authentication-method: "basic"
            authorization-grant-type: "authorization_code"

        provider:
          my-oauth-provider:
            authorization-uri: "https://my-auth-server/oauth/authorize"
            token-uri: "https://my-auth-server/oauth/token"
            user-info-uri: "https://my-auth-server/userinfo"
            user-info-authentication-method: "header"
            jwk-set-uri: "https://my-auth-server/token_keys"
            user-name-attribute: "name"

For OpenID Connect providers that support OpenID Connect discovery, the configuration can be further simplified. The provider needs to be configured with an issuer-uri which is the URI that it asserts as its Issuer Identifier. For example, if the issuer-uri provided is "https://example.com", then an OpenID Provider Configuration Request will be made to "https://example.com/.well-known/openid-configuration". The result is expected to be an OpenID Provider Configuration Response. The following example shows how an OpenID Connect Provider can be configured with the issuer-uri:

Properties
spring.security.oauth2.client.provider.oidc-provider.issuer-uri=https://dev-123456.oktapreview.com/oauth2/default/
Yaml
spring:
  security:
    oauth2:
      client:
        provider:
          oidc-provider:
            issuer-uri: "https://dev-123456.oktapreview.com/oauth2/default/"

By default, Spring Security’s OAuth2LoginAuthenticationFilter only processes URLs matching /login/oauth2/code/*. If you want to customize the redirect-uri to use a different pattern, you need to provide configuration to process that custom pattern. For example, for servlet applications, you can add your own SecurityFilterChain that resembles the following:

Java
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.web.SecurityFilterChain;

@Configuration(proxyBeanMethods = false)
public class MyOAuthClientConfiguration {

    @Bean
    public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
        http.authorizeRequests((requests) -> requests.anyRequest().authenticated());
        http.oauth2Login((login) -> login.redirectionEndpoint().baseUri("custom-callback"));
        return http.build();
    }

}
Kotlin
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import org.springframework.security.config.annotation.web.builders.HttpSecurity
import org.springframework.security.web.SecurityFilterChain

@Configuration(proxyBeanMethods = false)
class MyOAuthClientConfiguration {

    @Bean
    fun securityFilterChain(http: HttpSecurity): SecurityFilterChain {
        http.authorizeRequests().anyRequest().authenticated()
        http.oauth2Login().redirectionEndpoint().baseUri("custom-callback")
        return http.build()
    }

}
Spring Boot auto-configures an InMemoryOAuth2AuthorizedClientService which is used by Spring Security for the management of client registrations. The InMemoryOAuth2AuthorizedClientService has limited capabilities and we recommend using it only for development environments. For production environments, consider using a JdbcOAuth2AuthorizedClientService or creating your own implementation of OAuth2AuthorizedClientService.
OAuth2 Client Registration for Common Providers

For common OAuth2 and OpenID providers, including Google, Github, Facebook, and Okta, we provide a set of provider defaults (google, github, facebook, and okta, respectively).

If you do not need to customize these providers, you can set the provider attribute to the one for which you need to infer defaults. Also, if the key for the client registration matches a default supported provider, Spring Boot infers that as well.

In other words, the two configurations in the following example use the Google provider:

Properties
spring.security.oauth2.client.registration.my-client.client-id=abcd
spring.security.oauth2.client.registration.my-client.client-secret=password
spring.security.oauth2.client.registration.my-client.provider=google
spring.security.oauth2.client.registration.google.client-id=abcd
spring.security.oauth2.client.registration.google.client-secret=password
Yaml
spring:
  security:
    oauth2:
      client:
        registration:
          my-client:
            client-id: "abcd"
            client-secret: "password"
            provider: "google"
          google:
            client-id: "abcd"
            client-secret: "password"
Resource Server

If you have spring-security-oauth2-resource-server on your classpath, Spring Boot can set up an OAuth2 Resource Server. For JWT configuration, a JWK Set URI or OIDC Issuer URI needs to be specified, as shown in the following examples:

Properties
spring.security.oauth2.resourceserver.jwt.jwk-set-uri=https://example.com/oauth2/default/v1/keys
Yaml
spring:
  security:
    oauth2:
      resourceserver:
        jwt:
          jwk-set-uri: "https://example.com/oauth2/default/v1/keys"
Properties
spring.security.oauth2.resourceserver.jwt.issuer-uri=https://dev-123456.oktapreview.com/oauth2/default/
Yaml
spring:
  security:
    oauth2:
      resourceserver:
        jwt:
          issuer-uri: "https://dev-123456.oktapreview.com/oauth2/default/"
If the authorization server does not support a JWK Set URI, you can configure the resource server with the Public Key used for verifying the signature of the JWT. This can be done using the spring.security.oauth2.resourceserver.jwt.public-key-location property, where the value needs to point to a file containing the public key in the PEM-encoded x509 format.

The spring.security.oauth2.resourceserver.jwt.audiences property can be used to specifify the expected values of the aud claim in JWTs. For example, to require JWTs to contain an aud claim with the value my-audience:

Properties
spring.security.oauth2.resourceserver.jwt.audiences[0]=my-audience
Yaml
spring:
  security:
    oauth2:
      resourceserver:
        jwt:
          audiences:
            - "my-audience"

The same properties are applicable for both servlet and reactive applications. Alternatively, you can define your own JwtDecoder bean for servlet applications or a ReactiveJwtDecoder for reactive applications.

In cases where opaque tokens are used instead of JWTs, you can configure the following properties to validate tokens through introspection:

Properties
spring.security.oauth2.resourceserver.opaquetoken.introspection-uri=https://example.com/check-token
spring.security.oauth2.resourceserver.opaquetoken.client-id=my-client-id
spring.security.oauth2.resourceserver.opaquetoken.client-secret=my-client-secret
Yaml
spring:
  security:
    oauth2:
      resourceserver:
        opaquetoken:
          introspection-uri: "https://example.com/check-token"
          client-id: "my-client-id"
          client-secret: "my-client-secret"

Again, the same properties are applicable for both servlet and reactive applications. Alternatively, you can define your own OpaqueTokenIntrospector bean for servlet applications or a ReactiveOpaqueTokenIntrospector for reactive applications.

Authorization Server

Currently, Spring Security does not provide support for implementing an OAuth 2.0 Authorization Server. However, this functionality is available from the Spring Security OAuth project, which will eventually be superseded by Spring Security completely. Until then, you can use the spring-security-oauth2-autoconfigure module to easily set up an OAuth 2.0 authorization server; see its documentation for instructions.

8.4.4. SAML 2.0

Relying Party

If you have spring-security-saml2-service-provider on your classpath, you can take advantage of some auto-configuration to set up a SAML 2.0 Relying Party. This configuration makes use of the properties under Saml2RelyingPartyProperties.

A relying party registration represents a paired configuration between an Identity Provider, IDP, and a Service Provider, SP. You can register multiple relying parties under the spring.security.saml2.relyingparty prefix, as shown in the following example:

Properties
spring.security.saml2.relyingparty.registration.my-relying-party1.signing.credentials[0].private-key-location=path-to-private-key
spring.security.saml2.relyingparty.registration.my-relying-party1.signing.credentials[0].certificate-location=path-to-certificate
spring.security.saml2.relyingparty.registration.my-relying-party1.decryption.credentials[0].private-key-location=path-to-private-key
spring.security.saml2.relyingparty.registration.my-relying-party1.decryption.credentials[0].certificate-location=path-to-certificate
spring.security.saml2.relyingparty.registration.my-relying-party1.singlelogout.url=https://myapp/logout/saml2/slo
spring.security.saml2.relyingparty.registration.my-relying-party1.singlelogout.response-url=https://remoteidp2.slo.url
spring.security.saml2.relyingparty.registration.my-relying-party1.singlelogout.binding=POST
spring.security.saml2.relyingparty.registration.my-relying-party1.assertingparty.verification.credentials[0].certificate-location=path-to-verification-cert
spring.security.saml2.relyingparty.registration.my-relying-party1.assertingparty.entity-id=remote-idp-entity-id1
spring.security.saml2.relyingparty.registration.my-relying-party1.assertingparty.sso-url=https://remoteidp1.sso.url

spring.security.saml2.relyingparty.registration.my-relying-party2.signing.credentials[0].private-key-location=path-to-private-key
spring.security.saml2.relyingparty.registration.my-relying-party2.signing.credentials[0].certificate-location=path-to-certificate
spring.security.saml2.relyingparty.registration.my-relying-party2.decryption.credentials[0].private-key-location=path-to-private-key
spring.security.saml2.relyingparty.registration.my-relying-party2.decryption.credentials[0].certificate-location=path-to-certificate
spring.security.saml2.relyingparty.registration.my-relying-party2.assertingparty.verification.credentials[0].certificate-location=path-to-other-verification-cert
spring.security.saml2.relyingparty.registration.my-relying-party2.assertingparty.entity-id=remote-idp-entity-id2
spring.security.saml2.relyingparty.registration.my-relying-party2.assertingparty.sso-url=https://remoteidp2.sso.url
spring.security.saml2.relyingparty.registration.my-relying-party2.assertingparty.singlelogout.url=https://remoteidp2.slo.url
spring.security.saml2.relyingparty.registration.my-relying-party2.assertingparty.singlelogout.reponse-url=https://myapp/logout/saml2/slo
spring.security.saml2.relyingparty.registration.my-relying-party2.assertingparty.singlelogout.binding=POST
Yaml
spring:
  security:
    saml2:
      relyingparty:
        registration:
          my-relying-party1:
            signing:
              credentials:
              - private-key-location: "path-to-private-key"
                certificate-location: "path-to-certificate"
            decryption:
              credentials:
              - private-key-location: "path-to-private-key"
                certificate-location: "path-to-certificate"
            singlelogout:
               url: "https://myapp/logout/saml2/slo"
               response-url: "https://remoteidp2.slo.url"
               binding: "POST"
            assertingparty:
              verification:
                credentials:
                - certificate-location: "path-to-verification-cert"
              entity-id: "remote-idp-entity-id1"
              sso-url: "https://remoteidp1.sso.url"

          my-relying-party2:
            signing:
              credentials:
              - private-key-location: "path-to-private-key"
                certificate-location: "path-to-certificate"
            decryption:
              credentials:
              - private-key-location: "path-to-private-key"
                certificate-location: "path-to-certificate"
            assertingparty:
              verification:
                credentials:
                - certificate-location: "path-to-other-verification-cert"
              entity-id: "remote-idp-entity-id2"
              sso-url: "https://remoteidp2.sso.url"
              singlelogout:
                url: "https://remoteidp2.slo.url"
                reponse-url: "https://myapp/logout/saml2/slo"
                binding: "POST"

For SAML2 logout, by default, Spring Security’s Saml2LogoutRequestFilter and Saml2LogoutResponseFilter only process URLs matching /logout/saml2/slo. If you want to customize the url to which AP-initiated logout requests get sent to or the response-url to which an AP sends logout responses to, to use a different pattern, you need to provide configuration to process that custom pattern. For example, for servlet applications, you can add your own SecurityFilterChain that resembles the following:

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.web.SecurityFilterChain;

@Configuration(proxyBeanMethods = false)
public class MySamlRelyingPartyConfiguration {

    @Bean
    public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
        http.authorizeRequests().anyRequest().authenticated();
        http.saml2Login();
        http.saml2Logout((saml2) -> saml2.logoutRequest((request) -> request.logoutUrl("/SLOService.saml2"))
            .logoutResponse((response) -> response.logoutUrl("/SLOService.saml2")));
        return http.build();
    }

}

8.5. Spring Session

Spring Boot provides Spring Session auto-configuration for a wide range of data stores. When building a servlet web application, the following stores can be auto-configured:

  • JDBC

  • Redis

  • Hazelcast

  • MongoDB

The servlet auto-configuration replaces the need to use @Enable*HttpSession.

When building a reactive web application, the following stores can be auto-configured:

  • Redis

  • MongoDB

The reactive auto-configuration replaces the need to use @Enable*WebSession.

If a single Spring Session module is present on the classpath, Spring Boot uses that store implementation automatically. If you have more than one implementation, you must choose the StoreType that you wish to use to store the sessions. For instance, to use JDBC as the back-end store, you can configure your application as follows:

Properties
spring.session.store-type=jdbc
Yaml
spring:
  session:
    store-type: "jdbc"
You can disable Spring Session by setting the store-type to none.

Each store has specific additional settings. For instance, it is possible to customize the name of the table for the JDBC store, as shown in the following example:

Properties
spring.session.jdbc.table-name=SESSIONS
Yaml
spring:
  session:
    jdbc:
      table-name: "SESSIONS"

For setting the timeout of the session you can use the spring.session.timeout property. If that property is not set with a servlet web application, the auto-configuration falls back to the value of server.servlet.session.timeout.

You can take control over Spring Session’s configuration using @Enable*HttpSession (servlet) or @Enable*WebSession (reactive). This will cause the auto-configuration to back off. Spring Session can then be configured using the annotation’s attributes rather than the previously described configuration properties.

8.6. Spring for GraphQL

If you want to build GraphQL applications, you can take advantage of Spring Boot’s auto-configuration for Spring for GraphQL. The Spring for GraphQL project is based on GraphQL Java. You’ll need the spring-boot-starter-graphql starter at a minimum. Because GraphQL is transport-agnostic, you’ll also need to have one or more additional starters in your application to expose your GraphQL API over the web:

Starter Transport Implementation

spring-boot-starter-web

HTTP

Spring MVC

spring-boot-starter-websocket

WebSocket

WebSocket for Servlet apps

spring-boot-starter-webflux

HTTP, WebSocket

Spring WebFlux

spring-boot-starter-rsocket

TCP, WebSocket

Spring WebFlux on Reactor Netty

8.6.1. GraphQL Schema

A Spring GraphQL application requires a defined schema at startup. By default, you can write ".graphqls" or ".gqls" schema files under src/main/resources/graphql/** and Spring Boot will pick them up automatically. You can customize the locations with spring.graphql.schema.locations and the file extensions with spring.graphql.schema.file-extensions.

If you want Spring Boot to detect schema files in all your application modules and dependencies for that location, you can set spring.graphql.schema.locations to "classpath*:graphql/**/" (note the classpath*: prefix).

In the following sections, we’ll consider this sample GraphQL schema, defining two types and two queries:

type Query {
    greeting(name: String! = "Spring"): String!
    project(slug: ID!): Project
}

""" A Project in the Spring portfolio """
type Project {
    """ Unique string id used in URLs """
    slug: ID!
    """ Project name """
    name: String!
    """ URL of the git repository """
    repositoryUrl: String!
    """ Current support status """
    status: ProjectStatus!
}

enum ProjectStatus {
    """ Actively supported by the Spring team """
    ACTIVE
    """ Supported by the community """
    COMMUNITY
    """ Prototype, not officially supported yet  """
    INCUBATING
    """ Project being retired, in maintenance mode """
    ATTIC
    """ End-Of-Lifed """
    EOL
}
By default, field introspection will be allowed on the schema as it is required for tools such as GraphiQL. If you wish to not expose information about the schema, you can disable introspection by setting spring.graphql.schema.introspection.enabled to false.

8.6.2. GraphQL RuntimeWiring

The GraphQL Java RuntimeWiring.Builder can be used to register custom scalar types, directives, type resolvers, DataFetchers, and more. You can declare RuntimeWiringConfigurer beans in your Spring config to get access to the RuntimeWiring.Builder. Spring Boot detects such beans and adds them to the GraphQlSource builder.

Typically, however, applications will not implement DataFetcher directly and will instead create annotated controllers. Spring Boot will automatically detect @Controller classes with annotated handler methods and register those as DataFetchers. Here’s a sample implementation for our greeting query with a @Controller class:

Java
import org.springframework.graphql.data.method.annotation.Argument;
import org.springframework.graphql.data.method.annotation.QueryMapping;
import org.springframework.stereotype.Controller;

@Controller
public class GreetingController {

    @QueryMapping
    public String greeting(@Argument String name) {
        return "Hello, " + name + "!";
    }

}
Kotlin
;

import org.springframework.graphql.data.method.annotation.Argument
import org.springframework.graphql.data.method.annotation.QueryMapping
import org.springframework.stereotype.Controller

@Controller
class GreetingController {

    @QueryMapping
    fun greeting(@Argument name: String): String {
        return "Hello, $name!"
    }

}

8.6.3. Querydsl and QueryByExample Repositories Support

Spring Data offers support for both Querydsl and QueryByExample repositories. Spring GraphQL can configure Querydsl and QueryByExample repositories as DataFetcher.

Spring Data repositories annotated with @GraphQlRepository and extending one of:

  • QuerydslPredicateExecutor

  • ReactiveQuerydslPredicateExecutor

  • QueryByExampleExecutor

  • ReactiveQueryByExampleExecutor

are detected by Spring Boot and considered as candidates for DataFetcher for matching top-level queries.

8.6.4. Transports

HTTP and WebSocket

The GraphQL HTTP endpoint is at HTTP POST /graphql by default. The path can be customized with spring.graphql.path.

The HTTP endpoint for both Spring MVC and Spring WebFlux is provided by a RouterFunction bean with an @Order of 0. If you define your own RouterFunction beans, you may want to add appropriate @Order annotations to ensure that they are sorted correctly.

The GraphQL WebSocket endpoint is off by default. To enable it:

  • For a Servlet application, add the WebSocket starter spring-boot-starter-websocket

  • For a WebFlux application, no additional dependency is required

  • For both, the spring.graphql.websocket.path application property must be set

Spring GraphQL provides a Web Interception model. This is quite useful for retrieving information from an HTTP request header and set it in the GraphQL context or fetching information from the same context and writing it to a response header. With Spring Boot, you can declare a WebInterceptor bean to have it registered with the web transport.

Spring MVC and Spring WebFlux support CORS (Cross-Origin Resource Sharing) requests. CORS is a critical part of the web config for GraphQL applications that are accessed from browsers using different domains.

Spring Boot supports many configuration properties under the spring.graphql.cors.* namespace; here’s a short configuration sample:

Properties
spring.graphql.cors.allowed-origins=https://example.org
spring.graphql.cors.allowed-methods=GET,POST
spring.graphql.cors.max-age=1800s
Yaml
spring:
  graphql:
    cors:
      allowed-origins: "https://example.org"
      allowed-methods: GET,POST
      max-age: 1800s
RSocket

RSocket is also supported as a transport, on top of WebSocket or TCP. Once the RSocket server is configured, we can configure our GraphQL handler on a particular route using spring.graphql.rsocket.mapping. For example, configuring that mapping as "graphql" means we can use that as a route when sending requests with the RSocketGraphQlClient.

Spring Boot auto-configures a RSocketGraphQlClient.Builder<?> bean that you can inject in your components:

Java
@Component
public class RSocketGraphQlClientExample {

    private final RSocketGraphQlClient graphQlClient;

    public RSocketGraphQlClientExample(RSocketGraphQlClient.Builder<?> builder) {
        this.graphQlClient = builder.tcp("example.spring.io", 8181).route("graphql").build();
    }
Kotlin
@Component
class RSocketGraphQlClientExample(private val builder: RSocketGraphQlClient.Builder<*>) {

And then send a request:

Java
Mono<Book> book = this.graphQlClient.document("{ bookById(id: \"book-1\"){ id name pageCount author } }")
    .retrieve("bookById")
    .toEntity(Book.class);
Kotlin
val book = graphQlClient.document(
    """
    {
        bookById(id: "book-1"){
            id
            name
            pageCount
            author
        }
    }               
    """
)
    .retrieve("bookById").toEntity(Book::class.java)

8.6.5. Exception Handling

Spring GraphQL enables applications to register one or more Spring DataFetcherExceptionResolver components that are invoked sequentially. The Exception must be resolved to a list of graphql.GraphQLError objects, see Spring GraphQL exception handling documentation. Spring Boot will automatically detect DataFetcherExceptionResolver beans and register them with the GraphQlSource.Builder.

8.6.6. GraphiQL and Schema printer

Spring GraphQL offers infrastructure for helping developers when consuming or developing a GraphQL API.

Spring GraphQL ships with a default GraphiQL page that is exposed at "/graphiql" by default. This page is disabled by default and can be turned on with the spring.graphql.graphiql.enabled property. Many applications exposing such a page will prefer a custom build. A default implementation is very useful during development, this is why it is exposed automatically with spring-boot-devtools during development.

You can also choose to expose the GraphQL schema in text format at /graphql/schema when the spring.graphql.schema.printer.enabled property is enabled.

8.7. Spring HATEOAS

If you develop a RESTful API that makes use of hypermedia, Spring Boot provides auto-configuration for Spring HATEOAS that works well with most applications. The auto-configuration replaces the need to use @EnableHypermediaSupport and registers a number of beans to ease building hypermedia-based applications, including a LinkDiscoverers (for client side support) and an ObjectMapper configured to correctly marshal responses into the desired representation. The ObjectMapper is customized by setting the various spring.jackson.* properties or, if one exists, by a Jackson2ObjectMapperBuilder bean.

You can take control of Spring HATEOAS’s configuration by using @EnableHypermediaSupport. Note that doing so disables the ObjectMapper customization described earlier.

spring-boot-starter-hateoas is specific to Spring MVC and should not be combined with Spring WebFlux. In order to use Spring HATEOAS with Spring WebFlux, you can add a direct dependency on org.springframework.hateoas:spring-hateoas along with spring-boot-starter-webflux.

By default, requests that accept application/json will receive an application/hal+json response. To disable this behavior set spring.hateoas.use-hal-as-default-json-media-type to false and define a HypermediaMappingInformation or HalConfiguration to configure Spring HATEOAS to meet the needs of your application and its clients.

8.8. What to Read Next

You should now have a good understanding of how to develop web applications with Spring Boot. The next few sections describe how Spring Boot integrates with various data technologies, messaging systems, and other IO capabilities. You can pick any of these based on your application’s needs.

9. Data

Spring Boot integrates with a number of data technologies, both SQL and NoSQL.

9.1. SQL Databases

The Spring Framework provides extensive support for working with SQL databases, from direct JDBC access using JdbcTemplate to complete “object relational mapping” technologies such as Hibernate. Spring Data provides an additional level of functionality: creating Repository implementations directly from interfaces and using conventions to generate queries from your method names.

9.1.1. Configure a DataSource

Java’s javax.sql.DataSource interface provides a standard method of working with database connections. Traditionally, a 'DataSource' uses a URL along with some credentials to establish a database connection.

See the “How-to” section for more advanced examples, typically to take full control over the configuration of the DataSource.
Embedded Database Support

It is often convenient to develop applications by using an in-memory embedded database. Obviously, in-memory databases do not provide persistent storage. You need to populate your database when your application starts and be prepared to throw away data when your application ends.

The “How-to” section includes a section on how to initialize a database.

Spring Boot can auto-configure embedded H2, HSQL, and Derby databases. You need not provide any connection URLs. You need only include a build dependency to the embedded database that you want to use. If there are multiple embedded databases on the classpath, set the spring.datasource.embedded-database-connection configuration property to control which one is used. Setting the property to none disables auto-configuration of an embedded database.

If you are using this feature in your tests, you may notice that the same database is reused by your whole test suite regardless of the number of application contexts that you use. If you want to make sure that each context has a separate embedded database, you should set spring.datasource.generate-unique-name to true.

For example, the typical POM dependencies would be as follows:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
    <groupId>org.hsqldb</groupId>
    <artifactId>hsqldb</artifactId>
    <scope>runtime</scope>
</dependency>
You need a dependency on spring-jdbc for an embedded database to be auto-configured. In this example, it is pulled in transitively through spring-boot-starter-data-jpa.
If, for whatever reason, you do configure the connection URL for an embedded database, take care to ensure that the database’s automatic shutdown is disabled. If you use H2, you should use DB_CLOSE_ON_EXIT=FALSE to do so. If you use HSQLDB, you should ensure that shutdown=true is not used. Disabling the database’s automatic shutdown lets Spring Boot control when the database is closed, thereby ensuring that it happens once access to the database is no longer needed.
Connection to a Production Database

Production database connections can also be auto-configured by using a pooling DataSource.

DataSource Configuration

DataSource configuration is controlled by external configuration properties in spring.datasource.*. For example, you might declare the following section in application.properties:

Properties
spring.datasource.url=jdbc:mysql://localhost/test
spring.datasource.username=dbuser
spring.datasource.password=dbpass
Yaml
spring:
  datasource:
    url: "jdbc:mysql://localhost/test"
    username: "dbuser"
    password: "dbpass"
You should at least specify the URL by setting the spring.datasource.url property. Otherwise, Spring Boot tries to auto-configure an embedded database.
Spring Boot can deduce the JDBC driver class for most databases from the URL. If you need to specify a specific class, you can use the spring.datasource.driver-class-name property.
For a pooling DataSource to be created, we need to be able to verify that a valid Driver class is available, so we check for that before doing anything. In other words, if you set spring.datasource.driver-class-name=com.mysql.jdbc.Driver, then that class has to be loadable.

See DataSourceProperties for more of the supported options. These are the standard options that work regardless of the actual implementation. It is also possible to fine-tune implementation-specific settings by using their respective prefix (spring.datasource.hikari.*, spring.datasource.tomcat.*, spring.datasource.dbcp2.*, and spring.datasource.oracleucp.*). See the documentation of the connection pool implementation you are using for more details.

For instance, if you use the Tomcat connection pool, you could customize many additional settings, as shown in the following example:

Properties
spring.datasource.tomcat.max-wait=10000
spring.datasource.tomcat.max-active=50
spring.datasource.tomcat.test-on-borrow=true
Yaml
spring:
  datasource:
    tomcat:
      max-wait: 10000
      max-active: 50
      test-on-borrow: true

This will set the pool to wait 10000ms before throwing an exception if no connection is available, limit the maximum number of connections to 50 and validate the connection before borrowing it from the pool.

Supported Connection Pools

Spring Boot uses the following algorithm for choosing a specific implementation:

  1. We prefer HikariCP for its performance and concurrency. If HikariCP is available, we always choose it.

  2. Otherwise, if the Tomcat pooling DataSource is available, we use it.

  3. Otherwise, if Commons DBCP2 is available, we use it.

  4. If none of HikariCP, Tomcat, and DBCP2 are available and if Oracle UCP is available, we use it.

If you use the spring-boot-starter-jdbc or spring-boot-starter-data-jpa “starters”, you automatically get a dependency to HikariCP.

You can bypass that algorithm completely and specify the connection pool to use by setting the spring.datasource.type property. This is especially important if you run your application in a Tomcat container, as tomcat-jdbc is provided by default.

Additional connection pools can always be configured manually, using DataSourceBuilder. If you define your own DataSource bean, auto-configuration does not occur. The following connection pools are supported by DataSourceBuilder:

  • HikariCP

  • Tomcat pooling Datasource

  • Commons DBCP2

  • Oracle UCP & OracleDataSource

  • Spring Framework’s SimpleDriverDataSource

  • H2 JdbcDataSource

  • PostgreSQL PGSimpleDataSource

  • C3P0

Connection to a JNDI DataSource

If you deploy your Spring Boot application to an Application Server, you might want to configure and manage your DataSource by using your Application Server’s built-in features and access it by using JNDI.

The spring.datasource.jndi-name property can be used as an alternative to the spring.datasource.url, spring.datasource.username, and spring.datasource.password properties to access the DataSource from a specific JNDI location. For example, the following section in application.properties shows how you can access a JBoss AS defined DataSource:

Properties
spring.datasource.jndi-name=java:jboss/datasources/customers
Yaml
spring:
  datasource:
    jndi-name: "java:jboss/datasources/customers"

9.1.2. Using JdbcTemplate

Spring’s JdbcTemplate and NamedParameterJdbcTemplate classes are auto-configured, and you can @Autowire them directly into your own beans, as shown in the following example:

Java
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

    private final JdbcTemplate jdbcTemplate;

    public MyBean(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    public void doSomething() {
        this.jdbcTemplate ...
    }

}
Kotlin
import org.springframework.jdbc.core.JdbcTemplate
import org.springframework.stereotype.Component

@Component
class MyBean(private val jdbcTemplate: JdbcTemplate) {

    fun doSomething() {
        jdbcTemplate.execute("delete from customer")
    }

}

You can customize some properties of the template by using the spring.jdbc.template.* properties, as shown in the following example:

Properties
spring.jdbc.template.max-rows=500
Yaml
spring:
  jdbc:
    template:
      max-rows: 500
The NamedParameterJdbcTemplate reuses the same JdbcTemplate instance behind the scenes. If more than one JdbcTemplate is defined and no primary candidate exists, the NamedParameterJdbcTemplate is not auto-configured.

9.1.3. JPA and Spring Data JPA

The Java Persistence API is a standard technology that lets you “map” objects to relational databases. The spring-boot-starter-data-jpa POM provides a quick way to get started. It provides the following key dependencies:

  • Hibernate: One of the most popular JPA implementations.

  • Spring Data JPA: Helps you to implement JPA-based repositories.

  • Spring ORM: Core ORM support from the Spring Framework.

We do not go into too many details of JPA or Spring Data here. You can follow the “Accessing Data with JPA” guide from spring.io and read the Spring Data JPA and Hibernate reference documentation.
Entity Classes

Traditionally, JPA “Entity” classes are specified in a persistence.xml file. With Spring Boot, this file is not necessary and “Entity Scanning” is used instead. By default the auto-configuration packages are scanned.

Any classes annotated with @Entity, @Embeddable, or @MappedSuperclass are considered. A typical entity class resembles the following example:

Java
import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

@Entity
public class City implements Serializable {

    @Id
    @GeneratedValue
    private Long id;

    @Column(nullable = false)
    private String name;

    @Column(nullable = false)
    private String state;

    // ... additional members, often include @OneToMany mappings

    protected City() {
        // no-args constructor required by JPA spec
        // this one is protected since it should not be used directly
    }

    public City(String name, String state) {
        this.name = name;
        this.state = state;
    }

    public String getName() {
        return this.name;
    }

    public String getState() {
        return this.state;
    }

    // ... etc

}
Kotlin
import java.io.Serializable
import javax.persistence.Column
import javax.persistence.Entity
import javax.persistence.GeneratedValue
import javax.persistence.Id

@Entity
class City : Serializable {

    @Id
    @GeneratedValue
    private val id: Long? = null

    @Column(nullable = false)
    var name: String? = null
        private set

    // ... etc
    @Column(nullable = false)
    var state: String? = null
        private set

    // ... additional members, often include @OneToMany mappings

    protected constructor() {
        // no-args constructor required by JPA spec
        // this one is protected since it should not be used directly
    }

    constructor(name: String?, state: String?) {
        this.name = name
        this.state = state
    }

}
You can customize entity scanning locations by using the @EntityScan annotation. See the “Separate @Entity Definitions from Spring Configuration” how-to.
Spring Data JPA Repositories

Spring Data JPA repositories are interfaces that you can define to access data. JPA queries are created automatically from your method names. For example, a CityRepository interface might declare a findAllByState(String state) method to find all the cities in a given state.

For more complex queries, you can annotate your method with Spring Data’s Query annotation.

Spring Data repositories usually extend from the Repository or CrudRepository interfaces. If you use auto-configuration, the auto-configuration packages are searched for repositories.

You can customize the locations to look for repositories using @EnableJpaRepositories.

The following example shows a typical Spring Data repository interface definition:

Java
import org.springframework.boot.docs.data.sql.jpaandspringdata.entityclasses.City;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.repository.Repository;

public interface CityRepository extends Repository<City, Long> {

    Page<City> findAll(Pageable pageable);

    City findByNameAndStateAllIgnoringCase(String name, String state);

}
Kotlin
import org.springframework.boot.docs.data.sql.jpaandspringdata.entityclasses.City
import org.springframework.data.domain.Page
import org.springframework.data.domain.Pageable
import org.springframework.data.repository.Repository

interface CityRepository : Repository<City?, Long?> {

    fun findAll(pageable: Pageable?): Page<City?>?

    fun findByNameAndStateAllIgnoringCase(name: String?, state: String?): City?

}

Spring Data JPA repositories support three different modes of bootstrapping: default, deferred, and lazy. To enable deferred or lazy bootstrapping, set the spring.data.jpa.repositories.bootstrap-mode property to deferred or lazy respectively. When using deferred or lazy bootstrapping, the auto-configured EntityManagerFactoryBuilder will use the context’s AsyncTaskExecutor, if any, as the bootstrap executor. If more than one exists, the one named applicationTaskExecutor will be used.

When using deferred or lazy bootstrapping, make sure to defer any access to the JPA infrastructure after the application context bootstrap phase. You can use SmartInitializingSingleton to invoke any initialization that requires the JPA infrastructure. For JPA components (such as converters) that are created as Spring beans, use ObjectProvider to delay the resolution of dependencies, if any.

We have barely scratched the surface of Spring Data JPA. For complete details, see the Spring Data JPA reference documentation.
Spring Data Envers Repositories

If Spring Data Envers is available, JPA repositories are auto-configured to support typical Envers queries.

To use Spring Data Envers, make sure your repository extends from RevisionRepository as shown in the following example:

Java
import org.springframework.boot.docs.data.sql.jpaandspringdata.entityclasses.Country;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.repository.Repository;
import org.springframework.data.repository.history.RevisionRepository;

public interface CountryRepository extends RevisionRepository<Country, Long, Integer>, Repository<Country, Long> {

    Page<Country> findAll(Pageable pageable);

}
Kotlin
import org.springframework.boot.docs.data.sql.jpaandspringdata.entityclasses.Country
import org.springframework.data.domain.Page
import org.springframework.data.domain.Pageable
import org.springframework.data.repository.Repository
import org.springframework.data.repository.history.RevisionRepository

interface CountryRepository :
        RevisionRepository<Country?, Long?, Int>,
        Repository<Country?, Long?> {

    fun findAll(pageable: Pageable?): Page<Country?>?

}
For more details, check the Spring Data Envers reference documentation.
Creating and Dropping JPA Databases

By default, JPA databases are automatically created only if you use an embedded database (H2, HSQL, or Derby). You can explicitly configure JPA settings by using spring.jpa.* properties. For example, to create and drop tables you can add the following line to your application.properties:

Properties
spring.jpa.hibernate.ddl-auto=create-drop
Yaml
spring:
  jpa:
    hibernate.ddl-auto: "create-drop"
Hibernate’s own internal property name for this (if you happen to remember it better) is hibernate.hbm2ddl.auto. You can set it, along with other Hibernate native properties, by using spring.jpa.properties.* (the prefix is stripped before adding them to the entity manager). The following line shows an example of setting JPA properties for Hibernate:
Properties
spring.jpa.properties.hibernate[globally_quoted_identifiers]=true
Yaml
spring:
  jpa:
    properties:
      hibernate:
        "globally_quoted_identifiers": "true"

The line in the preceding example passes a value of true for the hibernate.globally_quoted_identifiers property to the Hibernate entity manager.

By default, the DDL execution (or validation) is deferred until the ApplicationContext has started. There is also a spring.jpa.generate-ddl flag, but it is not used if Hibernate auto-configuration is active, because the ddl-auto settings are more fine-grained.

Open EntityManager in View

If you are running a web application, Spring Boot by default registers OpenEntityManagerInViewInterceptor to apply the “Open EntityManager in View” pattern, to allow for lazy loading in web views. If you do not want this behavior, you should set spring.jpa.open-in-view to false in your application.properties.

9.1.4. Spring Data JDBC

Spring Data includes repository support for JDBC and will automatically generate SQL for the methods on CrudRepository. For more advanced queries, a @Query annotation is provided.

Spring Boot will auto-configure Spring Data’s JDBC repositories when the necessary dependencies are on the classpath. They can be added to your project with a single dependency on spring-boot-starter-data-jdbc. If necessary, you can take control of Spring Data JDBC’s configuration by adding the @EnableJdbcRepositories annotation or an AbstractJdbcConfiguration subclass to your application.

For complete details of Spring Data JDBC, see the reference documentation.

9.1.5. Using H2’s Web Console

The H2 database provides a browser-based console that Spring Boot can auto-configure for you. The console is auto-configured when the following conditions are met:

If you are not using Spring Boot’s developer tools but would still like to make use of H2’s console, you can configure the spring.h2.console.enabled property with a value of true.
The H2 console is only intended for use during development, so you should take care to ensure that spring.h2.console.enabled is not set to true in production.
Changing the H2 Console’s Path

By default, the console is available at /h2-console. You can customize the console’s path by using the spring.h2.console.path property.

Accessing the H2 Console in a Secured Application

H2 Console uses frames and, as it is intended for development only, does not implement CSRF protection measures. If your application uses Spring Security, you need to configure it to

  • disable CSRF protection for requests against the console,

  • set the header X-Frame-Options to SAMEORIGIN on responses from the console.

More information on CSRF and the header X-Frame-Options can be found in the Spring Security Reference Guide.

In simple setups, a SecurityFilterChain like the following can be used:

Java
import org.springframework.boot.autoconfigure.security.servlet.PathRequest;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Profile;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.Order;
import org.springframework.security.config.Customizer;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.web.SecurityFilterChain;

@Profile("dev")
@Configuration(proxyBeanMethods = false)
public class DevProfileSecurityConfiguration {

    @Bean
    @Order(Ordered.HIGHEST_PRECEDENCE)
    SecurityFilterChain h2ConsoleSecurityFilterChain(HttpSecurity http) throws Exception {
        http.requestMatcher(PathRequest.toH2Console());
        http.authorizeRequests(yourCustomAuthorization());
        http.csrf((csrf) -> csrf.disable());
        http.headers((headers) -> headers.frameOptions().sameOrigin());
        return http.build();
    }


}
Kotlin
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import org.springframework.context.annotation.Profile
import org.springframework.core.Ordered
import org.springframework.core.annotation.Order
import org.springframework.security.config.Customizer
import org.springframework.security.config.annotation.web.builders.HttpSecurity
import org.springframework.security.web.SecurityFilterChain

@Profile("dev")
@Configuration(proxyBeanMethods = false)
class DevProfileSecurityConfiguration {

    @Bean
    @Order(Ordered.HIGHEST_PRECEDENCE)
    fun h2ConsoleSecurityFilterChain(http: HttpSecurity): SecurityFilterChain {
        return http.authorizeHttpRequests(yourCustomAuthorization())
            .csrf().disable()
            .headers().frameOptions().sameOrigin().and()
            .build()
    }


}
The H2 console is only intended for use during development. In production, disabling CSRF protection or allowing frames for a website may create severe security risks.
PathRequest.toH2Console() returns the correct request matcher also when the console’s path has been customized.

9.1.6. Using jOOQ

jOOQ Object Oriented Querying (jOOQ) is a popular product from Data Geekery which generates Java code from your database and lets you build type-safe SQL queries through its fluent API. Both the commercial and open source editions can be used with Spring Boot.

Code Generation

In order to use jOOQ type-safe queries, you need to generate Java classes from your database schema. You can follow the instructions in the jOOQ user manual. If you use the jooq-codegen-maven plugin and you also use the spring-boot-starter-parent “parent POM”, you can safely omit the plugin’s <version> tag. You can also use Spring Boot-defined version variables (such as h2.version) to declare the plugin’s database dependency. The following listing shows an example:

<plugin>
    <groupId>org.jooq</groupId>
    <artifactId>jooq-codegen-maven</artifactId>
    <executions>
        ...
    </executions>
    <dependencies>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <version>${h2.version}</version>
        </dependency>
    </dependencies>
    <configuration>
        <jdbc>
            <driver>org.h2.Driver</driver>
            <url>jdbc:h2:~/yourdatabase</url>
        </jdbc>
        <generator>
            ...
        </generator>
    </configuration>
</plugin>
Using DSLContext

The fluent API offered by jOOQ is initiated through the org.jooq.DSLContext interface. Spring Boot auto-configures a DSLContext as a Spring Bean and connects it to your application DataSource. To use the DSLContext, you can inject it, as shown in the following example:

Java
import java.util.GregorianCalendar;
import java.util.List;

import org.jooq.DSLContext;

import org.springframework.stereotype.Component;

import static org.springframework.boot.docs.data.sql.jooq.dslcontext.Tables.AUTHOR;

@Component
public class MyBean {

    private final DSLContext create;

    public MyBean(DSLContext dslContext) {
        this.create = dslContext;
    }


}
Kotlin
import org.jooq.DSLContext
import org.springframework.stereotype.Component
import java.util.GregorianCalendar

@Component
class MyBean(private val create: DSLContext) {


}
The jOOQ manual tends to use a variable named create to hold the DSLContext.

You can then use the DSLContext to construct your queries, as shown in the following example:

Java
public List<GregorianCalendar> authorsBornAfter1980() {
    return this.create.selectFrom(AUTHOR)
            .where(AUTHOR.DATE_OF_BIRTH.greaterThan(new GregorianCalendar(1980, 0, 1)))
            .fetch(AUTHOR.DATE_OF_BIRTH);
Kotlin
fun authorsBornAfter1980(): List<GregorianCalendar> {
    return create.selectFrom<Tables.TAuthorRecord>(Tables.AUTHOR)
        .where(Tables.AUTHOR?.DATE_OF_BIRTH?.greaterThan(GregorianCalendar(1980, 0, 1)))
        .fetch(Tables.AUTHOR?.DATE_OF_BIRTH)
}
jOOQ SQL Dialect

Unless the spring.jooq.sql-dialect property has been configured, Spring Boot determines the SQL dialect to use for your datasource. If Spring Boot could not detect the dialect, it uses DEFAULT.

Spring Boot can only auto-configure dialects supported by the open source version of jOOQ.
Customizing jOOQ

More advanced customizations can be achieved by defining your own DefaultConfigurationCustomizer bean that will be invoked prior to creating the org.jooq.Configuration @Bean. This takes precedence to anything that is applied by the auto-configuration.

You can also create your own org.jooq.Configuration @Bean if you want to take complete control of the jOOQ configuration.

9.1.7. Using R2DBC

The Reactive Relational Database Connectivity (R2DBC) project brings reactive programming APIs to relational databases. R2DBC’s io.r2dbc.spi.Connection provides a standard method of working with non-blocking database connections. Connections are provided by using a ConnectionFactory, similar to a DataSource with jdbc.

ConnectionFactory configuration is controlled by external configuration properties in spring.r2dbc.*. For example, you might declare the following section in application.properties:

Properties
spring.r2dbc.url=r2dbc:postgresql://localhost/test
spring.r2dbc.username=dbuser
spring.r2dbc.password=dbpass
Yaml
spring:
  r2dbc:
    url: "r2dbc:postgresql://localhost/test"
    username: "dbuser"
    password: "dbpass"
You do not need to specify a driver class name, since Spring Boot obtains the driver from R2DBC’s Connection Factory discovery.
At least the url should be provided. Information specified in the URL takes precedence over individual properties, that is name, username, password and pooling options.
The “How-to” section includes a section on how to initialize a database.

To customize the connections created by a ConnectionFactory, that is, set specific parameters that you do not want (or cannot) configure in your central database configuration, you can use a ConnectionFactoryOptionsBuilderCustomizer @Bean. The following example shows how to manually override the database port while the rest of the options are taken from the application configuration:

Java
import io.r2dbc.spi.ConnectionFactoryOptions;

import org.springframework.boot.autoconfigure.r2dbc.ConnectionFactoryOptionsBuilderCustomizer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration(proxyBeanMethods = false)
public class MyR2dbcConfiguration {

    @Bean
    public ConnectionFactoryOptionsBuilderCustomizer connectionFactoryPortCustomizer() {
        return (builder) -> builder.option(ConnectionFactoryOptions.PORT, 5432);
    }

}
Kotlin
import io.r2dbc.spi.ConnectionFactoryOptions
import org.springframework.boot.autoconfigure.r2dbc.ConnectionFactoryOptionsBuilderCustomizer
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration

@Configuration(proxyBeanMethods = false)
class MyR2dbcConfiguration {

    @Bean
    fun connectionFactoryPortCustomizer(): ConnectionFactoryOptionsBuilderCustomizer {
        return ConnectionFactoryOptionsBuilderCustomizer { builder ->
            builder.option(ConnectionFactoryOptions.PORT, 5432)
        }
    }

}

The following examples show how to set some PostgreSQL connection options:

Java
import java.util.HashMap;
import java.util.Map;

import io.r2dbc.postgresql.PostgresqlConnectionFactoryProvider;

import org.springframework.boot.autoconfigure.r2dbc.ConnectionFactoryOptionsBuilderCustomizer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration(proxyBeanMethods = false)
public class MyPostgresR2dbcConfiguration {

    @Bean
    public ConnectionFactoryOptionsBuilderCustomizer postgresCustomizer() {
        Map<String, String> options = new HashMap<>();
        options.put("lock_timeout", "30s");
        options.put("statement_timeout", "60s");
        return (builder) -> builder.option(PostgresqlConnectionFactoryProvider.OPTIONS, options);
    }

}
Kotlin
import io.r2dbc.postgresql.PostgresqlConnectionFactoryProvider
import org.springframework.boot.autoconfigure.r2dbc.ConnectionFactoryOptionsBuilderCustomizer
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration

@Configuration(proxyBeanMethods = false)
class MyPostgresR2dbcConfiguration {

    @Bean
    fun postgresCustomizer(): ConnectionFactoryOptionsBuilderCustomizer {
        val options: MutableMap<String, String> = HashMap()
        options["lock_timeout"] = "30s"
        options["statement_timeout"] = "60s"
        return ConnectionFactoryOptionsBuilderCustomizer { builder ->
            builder.option(PostgresqlConnectionFactoryProvider.OPTIONS, options)
        }
    }

}

When a ConnectionFactory bean is available, the regular JDBC DataSource auto-configuration backs off. If you want to retain the JDBC DataSource auto-configuration, and are comfortable with the risk of using the blocking JDBC API in a reactive application, add @Import(DataSourceAutoConfiguration.class) on a @Configuration class in your application to re-enable it.

Embedded Database Support

Similarly to the JDBC support, Spring Boot can automatically configure an embedded database for reactive usage. You need not provide any connection URLs. You need only include a build dependency to the embedded database that you want to use, as shown in the following example:

<dependency>
    <groupId>io.r2dbc</groupId>
    <artifactId>r2dbc-h2</artifactId>
    <scope>runtime</scope>
</dependency>

If you are using this feature in your tests, you may notice that the same database is reused by your whole test suite regardless of the number of application contexts that you use. If you want to make sure that each context has a separate embedded database, you should set spring.r2dbc.generate-unique-name to true.

Using DatabaseClient

A DatabaseClient bean is auto-configured, and you can @Autowire it directly into your own beans, as shown in the following example:

Java
import java.util.Map;

import reactor.core.publisher.Flux;

import org.springframework.r2dbc.core.DatabaseClient;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

    private final DatabaseClient databaseClient;

    public MyBean(DatabaseClient databaseClient) {
        this.databaseClient = databaseClient;
    }

    // ...

    public Flux<Map<String, Object>> someMethod() {
        return this.databaseClient.sql("select * from user").fetch().all();
    }

}
Kotlin
import org.springframework.r2dbc.core.DatabaseClient
import org.springframework.stereotype.Component
import reactor.core.publisher.Flux

@Component
class MyBean(private val databaseClient: DatabaseClient) {

    // ...

    fun someMethod(): Flux<Map<String, Any>> {
        return databaseClient.sql("select * from user").fetch().all()
    }

}
Spring Data R2DBC Repositories

Spring Data R2DBC repositories are interfaces that you can define to access data. Queries are created automatically from your method names. For example, a CityRepository interface might declare a findAllByState(String state) method to find all the cities in a given state.

For more complex queries, you can annotate your method with Spring Data’s Query annotation.

Spring Data repositories usually extend from the Repository or CrudRepository interfaces. If you use auto-configuration, the auto-configuration packages are searched for repositories.

The following example shows a typical Spring Data repository interface definition:

Java
import reactor.core.publisher.Mono;

import org.springframework.data.repository.Repository;

public interface CityRepository extends Repository<City, Long> {

    Mono<City> findByNameAndStateAllIgnoringCase(String name, String state);

}
Kotlin
import org.springframework.data.repository.Repository
import reactor.core.publisher.Mono

interface CityRepository : Repository<City?, Long?> {

    fun findByNameAndStateAllIgnoringCase(name: String?, state: String?): Mono<City?>?

}
We have barely scratched the surface of Spring Data R2DBC. For complete details, see the Spring Data R2DBC reference documentation.

9.2. Working with NoSQL Technologies

Spring Data provides additional projects that help you access a variety of NoSQL technologies, including:

Of these, Spring Boot provides auto-configuration for Cassandra, Couchbase, Elasticsearch, LDAP, MongoDB, Neo4J and Redis. Additionally, Spring Boot for Apache Geode provides auto-configuration for Apache Geode. You can make use of the other projects, but you must configure them yourself. See the appropriate reference documentation at spring.io/projects/spring-data.

Spring Boot also provides auto-configuration for InfluxDB and Solr clients.

9.2.1. Redis

Redis is a cache, message broker, and richly-featured key-value store. Spring Boot offers basic auto-configuration for the Lettuce and Jedis client libraries and the abstractions on top of them provided by Spring Data Redis.

There is a spring-boot-starter-data-redis “Starter” for collecting the dependencies in a convenient way. By default, it uses Lettuce. That starter handles both traditional and reactive applications.

We also provide a spring-boot-starter-data-redis-reactive “Starter” for consistency with the other stores with reactive support.
Connecting to Redis

You can inject an auto-configured RedisConnectionFactory, StringRedisTemplate, or vanilla RedisTemplate instance as you would any other Spring Bean. The following listing shows an example of such a bean:

Java
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

    private final StringRedisTemplate template;

    public MyBean(StringRedisTemplate template) {
        this.template = template;
    }

    // ...

    public Boolean someMethod() {
        return this.template.hasKey("spring");
    }

}
Kotlin
import org.springframework.data.redis.core.StringRedisTemplate
import org.springframework.stereotype.Component

@Component
class MyBean(private val template: StringRedisTemplate) {

    // ...

    fun someMethod(): Boolean {
        return template.hasKey("spring")
    }

}

By default, the instance tries to connect to a Redis server at localhost:6379. You can specify custom connection details using spring.redis.* properties, as shown in the following example:

Properties
spring.redis.host=localhost
spring.redis.port=6379
spring.redis.database=0
spring.redis.username=user
spring.redis.password=secret
Yaml
spring:
  redis:
    host: "localhost"
    port: 6379
    database: 0
    username: "user"
    password: "secret"
You can also register an arbitrary number of beans that implement LettuceClientConfigurationBuilderCustomizer for more advanced customizations. ClientResources can also be customized using ClientResourcesBuilderCustomizer. If you use Jedis, JedisClientConfigurationBuilderCustomizer is also available. Alternatively, you can register a bean of type RedisStandaloneConfiguration, RedisSentinelConfiguration, or RedisClusterConfiguration to take full control over the configuration.

If you add your own @Bean of any of the auto-configured types, it replaces the default (except in the case of RedisTemplate, when the exclusion is based on the bean name, redisTemplate, not its type).

By default, a pooled connection factory is auto-configured if commons-pool2 is on the classpath.

9.2.2. MongoDB

MongoDB is an open-source NoSQL document database that uses a JSON-like schema instead of traditional table-based relational data. Spring Boot offers several conveniences for working with MongoDB, including the spring-boot-starter-data-mongodb and spring-boot-starter-data-mongodb-reactive “Starters”.

Connecting to a MongoDB Database

To access MongoDB databases, you can inject an auto-configured org.springframework.data.mongodb.MongoDatabaseFactory. By default, the instance tries to connect to a MongoDB server at mongodb://localhost/test. The following example shows how to connect to a MongoDB database:

Java
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;

import org.springframework.data.mongodb.MongoDatabaseFactory;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

    private final MongoDatabaseFactory mongo;

    public MyBean(MongoDatabaseFactory mongo) {
        this.mongo = mongo;
    }

    // ...

    public MongoCollection<Document> someMethod() {
        MongoDatabase db = this.mongo.getMongoDatabase();
        return db.getCollection("users");
    }

}
Kotlin
import com.mongodb.client.MongoCollection
import org.bson.Document
import org.springframework.data.mongodb.MongoDatabaseFactory
import org.springframework.stereotype.Component

@Component
class MyBean(private val mongo: MongoDatabaseFactory) {

    // ...

    fun someMethod(): MongoCollection<Document> {
        val db = mongo.mongoDatabase
        return db.getCollection("users")
    }

}

If you have defined your own MongoClient, it will be used to auto-configure a suitable MongoDatabaseFactory.

The auto-configured MongoClient is created using a MongoClientSettings bean. If you have defined your own MongoClientSettings, it will be used without modification and the spring.data.mongodb properties will be ignored. Otherwise a MongoClientSettings will be auto-configured and will have the spring.data.mongodb properties applied to it. In either case, you can declare one or more MongoClientSettingsBuilderCustomizer beans to fine-tune the MongoClientSettings configuration. Each will be called in order with the MongoClientSetti