The following embedded servlet containers are supported out of the box:

You can also deploy Spring Boot applications to any Servlet 3.0+ compatible container.

You can use Spring Boot in the same way as any standard Java library. Simply 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; and there is nothing special about a Spring Boot application, so you can run and debug as you would any other Java program.

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

10.1.1 Maven installation

Spring Boot is compatible with Apache Maven 3.2 or above. If you don’t already have Maven installed you can follow the instructions at maven.apache.org.

	Tip
	On many operating systems Maven can be installed via a package manager. If you’re an OSX Homebrew user try brew install maven. Ubuntu users can run sudo apt-get install maven.

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

Here is a typical pom.xml file:

<?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 http://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>

    <!-- Inherit defaults from Spring Boot -->
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.2.0.RELEASE</version>
    </parent>

    <!-- Add typical dependencies for a web application -->
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>

    <!-- Package as an executable jar -->
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

	Tip
	The spring-boot-starter-parent is a great way to use Spring Boot, but it might not be suitable all of the time. Sometimes you may need to inherit from a different parent POM, or you might just not like our default settings. See Section 13.1.2, “Using Spring Boot without the parent POM” for an alternative solution that uses an import scope.

buildscript {
    repositories {
        jcenter()
        maven { url "http://repo.spring.io/snapshot" }
        maven { url "http://repo.spring.io/milestone" }
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:1.2.0.RELEASE")
    }
}

apply plugin: 'java'
apply plugin: 'spring-boot'

jar {
    baseName = 'myproject'
    version =  '0.0.1-SNAPSHOT'
}

repositories {
    jcenter()
    maven { url "http://repo.spring.io/snapshot" }
    maven { url "http://repo.spring.io/milestone" }
}

dependencies {
    compile("org.springframework.boot:spring-boot-starter-web")
    testCompile("org.springframework.boot:spring-boot-starter-test")
}

The Spring Boot CLI is a command line tool that can be used if you want to quickly prototype with Spring. It allows you to run Groovy scripts, which means that you have a familiar Java-like syntax, without so much boilerplate code.

You don’t need to use the CLI to work with Spring Boot but it’s definitely the quickest way to get a Spring application off the ground.

$ gvm install springboot
$ spring --version
Spring Boot v1.2.0.RELEASE

$ gvm install springboot dev /path/to/spring-boot/spring-boot-cli/target/spring-boot-cli-1.2.0.RELEASE-bin/spring-1.2.0.RELEASE/
$ gvm use springboot dev
$ spring --version
Spring CLI v1.2.0.RELEASE

$ gvm ls springboot

================================================================================
Available Springboot Versions
================================================================================
> + dev
* 1.2.0.RELEASE

================================================================================
+ - local version
* - installed
> - currently in use
================================================================================

10.2.3 OSX Homebrew installation

If you are on a Mac and using Homebrew, all you need to do to install the Spring Boot CLI is:

$ brew tap pivotal/tap
$ brew install springboot

Homebrew will install spring to /usr/local/bin.

	Note
	If you don’t see the formula, your installation of brew might be out-of-date. Just execute brew update and try again.

10.2.4 Command-line completion

Spring Boot CLI ships with scripts that provide command completion for 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. To run the script manually, e.g. if you have installed using GVM

$ . ~/.gvm/springboot/current/shell-completion/bash/spring
$ spring <HIT TAB HERE>
  grab  help  jar  run  test  version

	Note
	If you install Spring Boot CLI using Homebrew, the command-line completion scripts are automatically registered with your shell.

10.2.5 Quick start Spring CLI example

Here’s a really simple web application that you can use to test your installation. Create a file called app.groovy:

@RestController
class ThisWillActuallyRun {

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

}

Then simply run it from a shell:

$ spring run app.groovy

	Note
	It will take some time when you first run the application as dependencies are downloaded. Subsequent runs will be much quicker.

Open localhost:8080 in your favorite web browser and you should see the following output:

Hello World!

If you are upgrading from an earlier release of Spring Boot check the “release notes” hosted on the project wiki. You’ll find upgrade instructions along with a list of “new and noteworthy” features for each release.

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

We need to start by creating a Maven pom.xml file. The pom.xml is the recipe that will be 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 http://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>1.2.0.RELEASE</version>
    </parent>

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

</project>

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

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

Spring Boot provides a number of “Starter POMs” that make easy to add jars to your classpath. Our sample application has already used 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 “Starter POMs” simply provide dependencies that you are likely to need when developing a specific type of application. Since we are developing a web application, we will add a spring-boot-starter-web dependency — but before that, let’s look at what we currently have.

$ 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. Let’s edit our pom.xml and add the spring-boot-starter-web dependency just 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 will see that there are now a number of additional dependencies, including the Tomcat web server and Spring Boot itself.

To finish our application we need to create a single Java file. Maven will compile sources from src/main/java by default so you need to create that folder structure, then add a file named src/main/java/Example.java:

import org.springframework.boot.*;
import org.springframework.boot.autoconfigure.*;
import org.springframework.stereotype.*;
import org.springframework.web.bind.annotation.*;

@RestController
@EnableAutoConfiguration
public class Example {

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

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

}

Although there isn’t much code here, quite a lot is going on. Let’s step through the important parts.

11.3.1 The @RestController and @RequestMapping annotations

The first annotation on our Example 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 will consider it when handling incoming web requests.

The @RequestMapping annotation provides “routing” information. It is telling 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.

	Tip
	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.

At this point our application should work. Since we have used the spring-boot-starter-parent POM we have a useful run goal that we can use to start the application. Type mvn spring-boot:run from the root project directory to start the application:

$ mvn spring-boot:run

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::  (v1.2.0.RELEASE)
....... . . .
....... . . . (log output here)
....... . . .
........ Started Example 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 hit ctrl-c.

Let’s 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.

To create an executable jar we need to add the spring-boot-maven-plugin to our pom.xml. 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>

	Note
	The spring-boot-starter-parent POM includes <executions> configuration to bind the repackage goal. If you are not using the parent POM you will need to declare this configuration yourself. See the plugin documentation for details.

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

$ 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:1.2.0.RELEASE: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 10 Mb in size. If you want to peek inside, you can use jar tvf:

$ 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:

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

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::  (v1.2.0.RELEASE)
....... . . .
....... . . . (log output here)
....... . . .
........ Started Example in 2.536 seconds (JVM running for 2.864)

As before, to gracefully exit the application hit ctrl-c.

Maven users can inherit from the spring-boot-starter-parent project to obtain sensible defaults. The parent project provides the following features:

On the last point: since the default config files files accept Spring style placeholders (${…​}) the Maven filtering is changed to use @..@ placeholders (you can override that with a Maven property resource.delimiter).

13.1.1 Inheriting the starter parent

To configure your project to inherit from the spring-boot-starter-parent simply set the parent:

<!-- Inherit defaults from Spring Boot -->
<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>1.2.0.RELEASE</version>
</parent>

	Note
	You should only need to specify the Spring Boot version number on this dependency. If you import additional starters, you can safely omit the version number.

<dependencyManagement>
     <dependencies>
        <dependency>
            <!-- Import dependency management from Spring Boot -->
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-dependencies</artifactId>
            <version>1.2.0.RELEASE</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

<properties>
    <java.version>1.8</java.version>
</properties>

13.1.4 Using the Spring Boot Maven plugin

Spring Boot includes a Maven plugin that can package the project as an executable jar. Add the plugin to your <plugins> section if you want to use it:

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

	Note
	If you use the Spring Boot starter parent pom, you only need to add the plugin, there is no need for to configure it unless you want to change the settings defined in the parent.

Gradle users can directly import “starter POMs” in their dependencies section. Unlike Maven, there is no “super parent” to import to share some configuration.

apply plugin: 'java'

repositories { jcenter() }
dependencies {
    compile("org.springframework.boot:spring-boot-starter-web:1.2.0.RELEASE")
}

The spring-boot-gradle-plugin is also available and provides tasks to create executable jars and run projects from source. It also adds a ResolutionStrategy that enables you to omit the version number for “blessed” dependencies:

buildscript {
    repositories { jcenter() }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:1.2.0.RELEASE")
    }
}

apply plugin: 'java'
apply plugin: 'spring-boot'

repositories { jcenter() }
dependencies {
    compile("org.springframework.boot:spring-boot-starter-web")
    testCompile("org.springframework.boot:spring-boot-starter-test")
}

It is possible to build a Spring Boot project using Apache Ant, however, no special support or plugins are provided. Ant scripts can use the Ivy dependency system to import starter POMs.

See the Section 73.8, “Build an executable archive with Ant” “How-to” for more complete instructions.

Starter POMs 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 technology 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, just include the spring-boot-starter-data-jpa dependency in your project, and you are good to go.

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.

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

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

Finally, Spring Boot includes some starters that can be used if you want to exclude or swap specific technical facets.

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

When a class doesn’t 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 @ComponentScan, @EntityScan or @SpringBootApplication annotations, since every class from every jar, will be read.

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

We generally recommend that you locate your main application class in a root package above other classes. The @EnableAutoConfiguration 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 @EnableAutoConfiguration annotated class will be used to search for @Entity items.

Using a root package also allows the @ComponentScan annotation to be used without needing to specify a basePackage attribute. You can also use the @SpringBootApplication annotation if your main class is in the root package.

Here is a typical layout:

com
 +- example
     +- myproject
         +- Application.java
         |
         +- domain
         |   +- Customer.java
         |   +- CustomerRepository.java
         |
         +- service
         |   +- CustomerService.java
         |
         +- web
             +- CustomerController.java

The Application.java file would declare the main method, along with the basic @Configuration.

package com.example.myproject;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

@Configuration
@EnableAutoConfiguration
@ComponentScan
public class Application {

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

}

You don’t need to 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 pickup all Spring components, including @Configuration classes.

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

Auto-configuration is noninvasive, 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 will back away.

If you need to find out what auto-configuration is currently being applied, and why, starting your application with the --debug switch. This will log an auto-configuration report to the console.

If you find that specific auto-configure classes are being applied that you don’t want, you can use the exclude attribute of @EnableAutoConfiguration to disable them.

import org.springframework.boot.autoconfigure.*;
import org.springframework.boot.autoconfigure.jdbc.*;
import org.springframework.context.annotation.*;

@Configuration
@EnableAutoConfiguration(exclude={DataSourceAutoConfiguration.class})
public class MyConfiguration {
}

You can run a Spring Boot application from your IDE as a simple Java application, however, first you will need to import your project. Import steps will 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 can’t directly import your project into your IDE, you may be able to generate IDE metadata using a build plugin. Maven includes plugins for Eclipse and IDEA; Gradle offers plugins for various IDEs.

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

If you use the Spring Boot Maven or Gradle plugins to create an executable jar you can run your application using java -jar. For example:

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

It is also possible to run a packaged application with remote debugging support enabled. This allows you to attach a debugger to your packaged application:

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

The Spring Boot Maven plugin includes a run goal which can be used to quickly compile and run your application. Applications run in an exploded form, and you can edit resources for instant “hot” reload.

$ mvn spring-boot:run

You might also want to use the useful operating system environment variable:

$ export MAVEN_OPTS=-Xmx1024m -XX:MaxPermSize=128M -Djava.security.egd=file:/dev/./urandom

(The “egd” setting is to speed up Tomcat startup by giving it a faster source of entropy for session keys.)

The Spring Boot Gradle plugin also includes a run goal which can be used to run your application in an exploded form. The bootRun task is added whenever you import the spring-boot-plugin

$ gradle bootRun

You might also want to use this useful operating system environment variable:

$ export JAVA_OPTS=-Xmx1024m -XX:MaxPermSize=128M -Djava.security.egd=file:/dev/./urandom

Since Spring Boot applications are just 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 the Spring Loaded project, or JRebel can be used.

See the Hot swapping “How-to” section for details.

The banner that is printed on start up can be changed by adding a banner.txt file to your classpath, or by setting banner.location to the location of such a file. If the file has an unusual encoding you can set banner.encoding (default is UTF-8).

You can use the following variables inside your banner.txt file:

	Tip
	The SpringBootApplication.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.

If the SpringApplication defaults aren’t to your taste you can instead create a local instance and customize it. For example, to turn off the banner you would write:

public static void main(String[] args) {
    SpringApplication app = new SpringApplication(MySpringConfiguration.class);
    app.setShowBanner(false);
    app.run(args);
}

	Note
	The constructor arguments passed to SpringApplication are configuration sources for spring beans. In most cases these will be references to @Configuration classes, but they could also be references to XML configuration or to packages that should be scanned.

It is also possible to configure the SpringApplication using an application.properties file. See Chapter 23, Externalized Configuration for details.

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

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

The SpringApplicationBuilder allows you to chain together multiple method calls, and includes parent and child methods that allow you to create a hierarchy.

For example:

new SpringApplicationBuilder()
    .showBanner(false)
    .sources(Parent.class)
    .child(Application.class)
    .run(args);

	Note
	There are some restrictions when creating an ApplicationContext hierarchy, e.g. Web components must be contained within the child context, and the same Environment will be used for both parent and child contexts. See the SpringApplicationBuilder javadoc for full details.

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.

You can register event listeners in a number of ways, the most common being SpringApplication.addListeners(…​) method.

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

	Tip
	You often won’t need to use application events, but it can be handy to know that they exist. Internally, Spring Boot uses events to handle a variety of tasks.

A SpringApplication will attempt to create the right type of ApplicationContext on your behalf. By default, an AnnotationConfigApplicationContext or AnnotationConfigEmbeddedWebApplicationContext will be used, depending on whether you are developing a web application or not.

The algorithm used to determine a ‘web environment’ is fairly simplistic (based on the presence of a few classes). You can use setWebEnvironment(boolean webEnvironment) if you need to override the default.

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

	Tip
	It is often desirable to call setWebEnvironment(false) when using SpringApplication within a JUnit test.

If you want access to the raw command line arguments, or you need to run some specific code once the SpringApplication has started you can implement the CommandLineRunner interface. The run(String…​ args) method will be called on all Spring beans implementing this interface.

import org.springframework.boot.*
import org.springframework.stereotype.*

@Component
public class MyBean implements CommandLineRunner {

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

}

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

Each SpringApplication will register a shutdown hook with the JVM to ensure that the ApplicationContext is closed 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 the application ends.

By default SpringApplication will convert any command line option arguments (starting with ‘--’, e.g. --server.port=9000) to a property and add it to the Spring Environment. As mentioned above, command line properties always take precedence over other property sources.

If you don’t want command line properties to be added to the Environment you can disable them using SpringApplication.setAddCommandLineProperties(false).

SpringApplication will load properties from application.properties files in the following locations and add them to the Spring Environment:

The list is ordered by precedence (locations higher in the list override lower items).

	Note
	You can also use YAML ('.yml') files as an alternative to '.properties'.

If you don’t like application.properties as the configuration file name you can switch to another by specifying a spring.config.name environment property. You can also refer to an explicit location using the spring.config.location environment property (comma-separated list of directory locations, or file paths).

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

or

$ java -jar myproject.jar --spring.config.location=classpath:/default.properties,classpath:/override.properties

If spring.config.location contains directories (as opposed to files) they should end in / (and will be appended with the names generated from spring.config.name before being loaded). The default search path classpath:,classpath:/config,file:,file:config/ is always used, irrespective of the value of spring.config.location. In that way you can set up default values for your application in application.properties (or whatever other basename you choose with spring.config.name) and override it at runtime with a different file, keeping the defaults.

	Note
	If you use environment variables rather than system properties, most operating systems disallow period-separated key names, but you can use underscores instead (e.g. SPRING_CONFIG_NAME instead of spring.config.name).

	Note
	If you are running in a container 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.

In addition to application.properties files, profile specific properties can also be defined using the naming convention application-{profile}.properties.

Profile specific properties are loaded from the same locations as standard application.properties, with profile specific files overriding the default ones.

The values in application.properties are filtered through the existing Environment when they are used so you can refer back to previously defined values (e.g. from System properties).

app.name=MyApp
app.description=${app.name} is a Spring Boot application

	Tip
	You can also use this technique to create ‘short’ variants of existing Spring Boot properties. See the Section 63.3, “Use ‘short’ command line arguments” how-to for details.

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

	Note
	If you use ‘starter POMs’ SnakeYAML will be automatically provided via spring-boot-starter.

environments:
    dev:
        url: http://dev.bar.com
        name: Developer Setup
    prod:
        url: http://foo.bar.com
        name: My Cool App

environments.dev.url=http://dev.bar.com
environments.dev.name=Developer Setup
environments.prod.url=http://foo.bar.com
environments.prod.name=My Cool App

my:
   servers:
       - dev.bar.com
       - foo.bar.com

my.servers[0]=dev.bar.com
my.servers[1]=foo.bar.com

@ConfigurationProperties(prefix="my")
public class Config {

    private List<String> servers = new ArrayList<String>();

    public List<String> getServers() {
        return this.servers;
    }
}

server:
    address: 192.168.1.100
---
spring:
    profiles: development
server:
    address: 127.0.0.1
---
spring:
    profiles: production
server:
    address: 192.168.1.120

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 allows strongly typed beans to govern and validate the configuration of your application. For example:

@Component
@ConfigurationProperties(prefix="connection")
public class ConnectionSettings {

    private String username;

    private InetAddress remoteAddress;

    // ... getters and setters

}

When the @EnableConfigurationProperties annotation is applied to your @Configuration, any beans annotated with @ConfigurationProperties will be automatically configured from the Environment properties. This style of configuration works particularly well with the SpringApplication external YAML configuration:

# application.yml

connection:
    username: admin
    remoteAddress: 192.168.1.1

# additional configuration as required

To work with @ConfigurationProperties beans you can just inject them in the same way as any other bean.

@Service
public class MyService {

    @Autowired
    private ConnectionSettings connection;

     //...

    @PostConstruct
    public void openConnection() {
        Server server = new Server();
        this.connection.configure(server);
    }

}

It is also possible to shortcut the registration of @ConfigurationProperties bean definitions by simply listing the properties classes directly in the @EnableConfigurationProperties annotation:

@Configuration
@EnableConfigurationProperties(ConnectionSettings.class)
public class MyConfiguration {
}

	Tip
	Using @ConfigurationProperties also allows you to generate meta-data files that can be used by IDEs. See the Appendix B, Configuration meta-data appendix for details.

23.6.2 @ConfigurationProperties Validation

Spring Boot will attempt to validate external configuration, by default using JSR-303 (if it is on the classpath). You can simply add JSR-303 javax.validation constraint annotations to your @ConfigurationProperties class:

@Component
@ConfigurationProperties(prefix="connection")
public class ConnectionSettings {

    @NotNull
    private InetAddress remoteAddress;

    // ... getters and setters

}

You can also add a custom Spring Validator by creating a bean definition called configurationPropertiesValidator.

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

The spring.profiles.active property follows the same ordering rules as other properties, the highest PropertySource will win. This means that you can specify active profiles in application.properties then replace them using the command line switch.

Sometimes it is useful to have profile specific properties that add to the active profiles rather than replace them. The spring.profiles.include property can be used to unconditionally add active profiles. The SpringApplication entry point also has a Java API for setting additional profiles (i.e. on top of those activated by the spring.profiles.active property): see the setAdditionalProfiles() method.

For example, when an application with following properties is run using the switch --spring.profiles.active=prod the proddb and prodmq profiles will also be activated:

---
my.property: fromyamlfile
---
spring.profiles: prod
spring.profiles.include: proddb,prodmq

	Note
	Remember that the spring.profiles property can be defined in a YAML document to determine when this particular document is included in the configuration. See Section 63.6, “Change configuration depending on the environment” for more details.

You can programmatically set active profiles by calling SpringApplication.setAdditionalProfiles(…​) before your application runs. It is also possible to activate profiles using Spring’s ConfigurableEnvironment interface.

Profile specific variants of both application.properties (or application.yml) and files referenced via @ConfigurationProperties are considered as files are loaded. See Section 23.3, “Profile specific properties” for details.

The default log output from Spring Boot looks like this:

2014-03-05 10:57:51.112  INFO 45469 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/7.0.52
2014-03-05 10:57:51.253  INFO 45469 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2014-03-05 10:57:51.253  INFO 45469 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1358 ms
2014-03-05 10:57:51.698  INFO 45469 --- [ost-startStop-1] o.s.b.c.e.ServletRegistrationBean        : Mapping servlet: 'dispatcherServlet' to [/]
2014-03-05 10:57:51.702  INFO 45469 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]

The following items are output:

The default log configuration will echo messages to the console as they are written. By default ERROR, WARN and INFO level messages are logged. To also log DEBUG level messages to the console you can start your application with a --debug flag.

$ java -jar myapp.jar --debug

If your terminal supports ANSI, color output will be used to aid readability. You can set spring.output.ansi.enabled to a supported value to override the auto detection.

By default, Spring Boot will only log to the console and will not write log files. If you want to write log files in addition to the console output you need to set the logging.file and/or logging.path properties (for example in your application.properties). Log files will rotate when they reach 10 Mb.

As with console output, ERROR, WARN and INFO level messages are logged by default.

The following table shows how the logging.* properties can be used together:

All the supported logging systems can have the logger levels set in the Spring Environment (so for example in application.properties) using ‘logging.level.*=LEVEL’ where ‘LEVEL’ is one of TRACE, DEBUG, INFO, WARN, ERROR, FATAL, OFF. Example application.properties:

logging.level.org.springframework.web: DEBUG
logging.level.org.hibernate: ERROR

The various logging systems can be activated by including the appropriate libraries on the classpath, and further customized by providing a suitable configuration file in the root of the classpath, or in a location specified by the Spring Environment property logging.config. (Note however that since logging is initialized before the ApplicationContext is created, it isn’t possible to control logging from @PropertySources in Spring @Configuration files. System properties and the conventional Spring Boot external configuration files work just fine.)

Depending on your logging system, the following files will be loaded:

To help with the customization some other properties are transferred from the Spring Environment to System properties:

All the logging systems supported can consult System properties when parsing their configuration files. See the default configurations in spring-boot.jar for examples.

	Warning
	There are know classloading issues with Java Util Logging that cause problems when running from an ‘executable jar’. We recommend that you avoid it if at all possible.

The Spring Web MVC framework (often referred to as simply ‘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 using @RequestMapping annotations.

Here is a typical example @RestController to serve JSON data:

@RestController
@RequestMapping(value="/users")
public class MyRestController {

    @RequestMapping(value="/{user}", method=RequestMethod.GET)
    public User getUser(@PathVariable Long user) {
        // ...
    }

    @RequestMapping(value="/{user}/customers", method=RequestMethod.GET)
    List<Customer> getUserCustomers(@PathVariable Long user) {
        // ...
    }

    @RequestMapping(value="/{user}", method=RequestMethod.DELETE)
    public User deleteUser(@PathVariable Long user) {
        // ...
    }

}

Spring MVC is part of the core Spring Framework and detailed information is available in the reference documentation. There are also several guides available at spring.io/guides that cover Spring MVC.

import org.springframework.boot.autoconfigure.web.HttpMessageConverters;
import org.springframework.context.annotation.*;
import org.springframework.http.converter.*;

@Configuration
public class MyConfiguration {

    @Bean
    public HttpMessageConverters customConverters() {
        HttpMessageConverter<?> additional = ...
        HttpMessageConverter<?> another = ...
        return new HttpMessageConverters(additional, another);
    }

}

26.1.4 Static Content

By default Spring Boot will serve static content from a folder 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 you can modify that behavior by adding your own WebMvcConfigurerAdapter and overriding the addResourceHandlers method.

In a stand-alone web application the default servlet from the container is also enabled, and acts as a fallback, serving content from the root of the ServletContext if Spring decides not to handle it. Most of the time this will not happen (unless you modify the default MVC configuration) because Spring will always be able to handle requests through the DispatcherServlet.

In addition to the ‘standard’ static resource locations above, a special case is made for Webjars content. Any resources with a path in /webjars/** will be served from jar files if they are packaged in the Webjars format.

	Tip
	Do not use the src/main/webapp folder if your application will be packaged as a jar. Although this folder is a common standard, it will only work with war packaging and it will be silently ignored by most build tools if you generate a jar.

26.1.5 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 Velocity, FreeMarker and JSPs. Many other templating engines also ship their own Spring MVC integrations.

Spring Boot includes auto-configuration support for the following templating engines:

• FreeMarker
• Groovy
• Thymeleaf
• Velocity

When you’re using one of these templating engines with the default configuration, your templates will be picked up automatically from src/main/resources/templates.

	Tip
	JSPs should be avoided if possible, there are several known limitations when using them with embedded servlet containers.

@Bean
public EmbeddedServletContainerCustomizer containerCustomizer(){
    return new MyCustomizer();
}

// ...

private static class MyCustomizer implements EmbeddedServletContainerCustomizer {

    @Override
    public void customize(ConfigurableEmbeddedServletContainer container) {
        container.addErrorPages(new ErrorPage(HttpStatus.BAD_REQUEST, "/400"));
    }

}

@Bean
public FilterRegistrationBean myFilter() {
    FilterRegistrationBean registration = new FilterRegistrationBean();
    registration.setFilter(new MyFilter());
    ...
    registration.setDispatcherTypes(EnumSet.allOf(DispatcherType.class));
    return registration;
}

If you prefer the JAX-RS programming model for REST endpoints you can use one of the available implementations instead of Spring MVC. Jersey 1.x and Apache Celtix work quite well out of the box if you just register their Servlet or Filter as a @Bean in your application context. Jersey 2.x 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 2.x just 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:

@Component
public class JerseyConfig extends ResourceConfig {

    public JerseyConfig() {
        register(Endpoint.class);
    }

}

All the registered endpoints should be @Components with HTTP resource annotations (@GET etc.), e.g.

@Component
@Path("/hello")
public class Endpoint {

    @GET
    public String message() {
        return "Hello";
    }

}

Since the Endpoint is a Spring @Component its lifecycle is managed by Spring and you can @Autowired dependencies and inject external configuration with @Value. The Jersey servlet will be registered and mapped to /* by default. You can change the mapping by adding @ApplicationPath to your ResourceConfig.

By default Jersey will be set up as a Servlet in a @Bean of type ServletRegistrationBean named jerseyServletRegistration. 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 servlet has an @Order which you can set with spring.jersey.filter.order. Both the Servlet and the Filter registrations can be given init parameters using spring.jersey.init.* to specify a map of properties.

There is a Jersey sample so you can see how to set things up. There is also a Jersey 1.x sample. Note that in the Jersey 1.x sample that the spring-boot maven plugin has been configured to unpack some Jersey jars so they can be scanned by the JAX-RS implementation (because the sample asks for them to be scanned in its Filter registration). You may need to do the same if any of your JAX-RS resources are packages as nested jars.

Spring Boot includes support for embedded Tomcat, Jetty, and Undertow servers. Most developers will simply use the appropriate ‘Starter POM’ to obtain a fully configured instance. By default the embedded server will listen for HTTP requests on port 8080.

26.3.2 The EmbeddedWebApplicationContext

Under the hood Spring Boot uses a new type of ApplicationContext for embedded servlet container support. The EmbeddedWebApplicationContext is a special type of WebApplicationContext that bootstraps itself by searching for a single EmbeddedServletContainerFactory bean. Usually a TomcatEmbeddedServletContainerFactory, JettyEmbeddedServletContainerFactory, or UndertowEmbeddedServletContainerFactory will have been auto-configured.

	Note
	You usually won’t need to be aware of these implementation classes. Most applications will be auto-configured and the appropriate ApplicationContext and EmbeddedServletContainerFactory will be created on your behalf.

import org.springframework.boot.context.embedded.*;
import org.springframework.stereotype.Component;

@Component
public class CustomizationBean implements EmbeddedServletContainerCustomizer {

    @Override
    public void customize(ConfigurableEmbeddedServletContainer container) {
        container.setPort(9000);
    }

}

@Bean
public EmbeddedServletContainerFactory servletContainer() {
    TomcatEmbeddedServletContainerFactory factory = new TomcatEmbeddedServletContainerFactory();
    factory.setPort(9000);
    factory.setSessionTimeout(10, TimeUnit.MINUTES);
    factory.addErrorPages(new ErrorPage(HttpStatus.404, "/notfound.html");
    return factory;
}

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.

28.1.1 Embedded Database Support

It’s often convenient to develop applications using an in-memory embedded database. Obviously, in-memory databases do not provide persistent storage; you will need to populate your database when your application starts and be prepared to throw away data when your application ends.

	Tip
	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 don’t need to provide any connection URLs, simply include a build dependency to the embedded database that you want to use.

For example, typical POM dependencies would be:

<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>

	Note
	You need a dependency on spring-jdbc for an embedded database to be auto-configured. In this example it’s pulled in transitively via spring-boot-starter-data-jpa.

28.1.2 Connection to a production database

Production database connections can also be auto-configured using a pooling DataSource. Here’s the algorithm for choosing a specific implementation:

• We prefer the Tomcat pooling DataSource for its performance and concurrency, so if that is available we always choose it.
• If HikariCP is available we will use it
• If Commons DBCP is available we will use it, but we don’t recommend it in production.
• Lastly, if Commons DBCP2 is available we will use it

If you use the spring-boot-starter-jdbc or spring-boot-starter-data-jpa ‘starter POMs’ you will automcatically get a dependency to tomcat-jdbc.

	Note
	Additional connection pools can always be configured manually. If you define your own DataSource bean, auto-configuration will not occur.

DataSource configuration is controlled by external configuration properties in spring.datasource.*. For example, you might declare the following section in application.properties:

spring.datasource.url=jdbc:mysql://localhost/test
spring.datasource.username=dbuser
spring.datasource.password=dbpass
spring.datasource.driver-class-name=com.mysql.jdbc.Driver

See DataSourceProperties for more of the supported options.

	Tip
	You often won’t need to specify the driver-class-name since Spring boot can deduce it for most databases from the url.

	Note
	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. I.e. if you set spring.datasource.driverClassName=com.mysql.jdbc.Driver then that class has to be loadable.

spring.datasource.jndi-name=java:jboss/datasources/customers

Spring’s JdbcTemplate and NamedParameterJdbcTemplate classes are auto-configured and you can @Autowire them directly into your own beans:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

    private final JdbcTemplate jdbcTemplate;

    @Autowired
    public MyBean(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    // ...

}

The Java Persistence API is a standard technology that allows you to ‘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:

	Tip
	We won’t 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.

28.3.1 Entity Classes

Traditionally, JPA ‘Entity’ classes are specified in a persistence.xml file. With Spring Boot this file is not necessary and instead ‘Entity Scanning’ is used. By default all packages below your main configuration class (the one annotated with @EnableAutoConfiguration or @SpringBootApplication) will be searched.

Any classes annotated with @Entity, @Embeddable or @MappedSuperclass will be considered. A typical entity class would look something like this:

package com.example.myapp.domain;

import java.io.Serializable;
import javax.persistence.*;

@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 shouldn't be used directly
    }

    public City(String name, String state) {
        this.name = name;
        this.country = country;
    }

    public String getName() {
        return this.name;
    }

    public String getState() {
        return this.state;
    }

    // ... etc

}

	Tip
	You can customize entity scanning locations using the @EntityScan annotation. See the Section 67.4, “Separate @Entity definitions from Spring configuration” how-to.

28.3.2 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 cities in a given state.

For more complex queries you can annotate your method using Spring Data’s Query annotation.

Spring Data repositories usually extend from the Repository or CrudRepository interfaces. If you are using auto-configuration, repositories will be searched from the package containing your main configuration class (the one annotated with @EnableAutoConfiguration or @SpringBootApplication) down.

Here is a typical Spring Data repository:

package com.example.myapp.domain;

import org.springframework.data.domain.*;
import org.springframework.data.repository.*;

public interface CityRepository extends Repository<City, Long> {

    Page<City> findAll(Pageable pageable);

    City findByNameAndCountryAllIgnoringCase(String name, String country);

}

	Tip
	We have barely scratched the surface of Spring Data JPA. For complete details check their reference documentation.

28.3.3 Creating and dropping JPA databases

By default, JPA databases will be automatically created only if you use an embedded database (H2, HSQL or Derby). You can explicitly configure JPA settings using spring.jpa.* properties. For example, to create and drop tables you can add the following to your application.properties.

spring.jpa.hibernate.ddl-auto=create-drop

	Note
	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, using spring.jpa.properties.* (the prefix is stripped before adding them to the entity manager). Example:

spring.jpa.properties.hibernate.globally_quoted_identifiers=true

passes hibernate.globally_quoted_identifiers 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 autoconfig is active because the ddl-auto settings are more fine-grained.

Redis is a cache, message broker and richly-featured key-value store. Spring Boot offers basic auto-configuration for the Jedis client library and abstractions on top of it provided by Spring Data Redis. There is a spring-boot-starter-redis ‘Starter POM’ for collecting the dependencies in a convenient way.

@Component
public class MyBean {

    private StringRedisTemplate template;

    @Autowired
    public MyBean(StringRedisTemplate template) {
        this.template = template;
    }

    // ...

}

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 The spring-boot-starter-data-mongodb ‘Starter POM’.

29.2.1 Connecting to a MongoDB database

You can inject an auto-configured org.springframework.data.mongodb.MongoDbFactory to access Mono databases. By default the instance will attempt to connect to a MongoDB server using the URL mongodb://localhost/test:

import org.springframework.data.mongodb.MongoDbFactory;
import import com.mongodb.DB;

@Component
public class MyBean {

    private final MongoDbFactory mongo;

    @Autowired
    public MyBean(MongoDbFactory mongo) {
        this.mongo = mongo;
    }

    // ...

    public void example() {
        DB db = mongo.getDb();
        // ...
    }

}

You can set spring.data.mongodb.uri property to change the url, or alternatively specify a host/port. For example, you might declare the following in your application.properties:

spring.data.mongodb.host=mongoserver
spring.data.mongodb.port=27017

	Tip
	If spring.data.mongodb.port is not specified the default of 27017 is used. You could simply delete this line from the sample above.

	Tip
	If you aren’t using Spring Data Mongo you can inject com.mongodb.Mongo beans instead of using MongoDbFactory.

You can also declare your own MongoDbFactory or Mongo @Beans if you want to take complete control of establishing the MongoDB connection.

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

    private final MongoTemplate mongoTemplate;

    @Autowired
    public MyBean(MongoTemplate mongoTemplate) {
        this.mongoTemplate = mongoTemplate;
    }

    // ...

}

29.2.3 Spring Data MongoDB repositories

Spring Data includes repository support for MongoDB. As with the JPA repositories discussed earlier, the basic principle is that queries are constructed for you automatically based on method names.

In fact, both Spring Data JPA and Spring Data MongoDB share the same common infrastructure; so you could take the JPA example from earlier and, assuming that City is now a Mongo data class rather than a JPA @Entity, it will work in the same way.

package com.example.myapp.domain;

import org.springframework.data.domain.*;
import org.springframework.data.repository.*;

public interface CityRepository extends Repository<City, Long> {

    Page<City> findAll(Pageable pageable);

    City findByNameAndCountryAllIgnoringCase(String name, String country);

}

	Tip
	For complete details of Spring Data MongoDB, including its rich object mapping technologies, refer to their reference documentation.

Spring Data Gemfire provides convenient Spring-friendly tools for accessing the Pivotal Gemfire data management platform. There is a spring-boot-starter-data-gemfire ‘Starter POM’ for collecting the dependencies in a convenient way. There is currently no auto=config support for Gemfire, but you can enable Spring Data Repositories with a single annotation.

Apache Solr is a search engine. Spring Boot offers basic auto-configuration for the solr client library and abstractions on top of it provided by Spring Data Solr. There is a spring-boot-starter-data-solr ‘Starter POM’ for collecting the dependencies in a convenient way.

@Component
public class MyBean {

    private SolrServer solr;

    @Autowired
    public MyBean(SolrServer solr) {
        this.solr = solr;
    }

    // ...

}

29.4.2 Spring Data Solr repositories

Spring Data includes repository support for Apache Solr. As with the JPA repositories discussed earlier, the basic principle is that queries are constructed for you automatically based on method names.

In fact, both Spring Data JPA and Spring Data Solr share the same common infrastructure; so you could take the JPA example from earlier and, assuming that City is now a @SolrDocument class rather than a JPA @Entity, it will work in the same way.

	Tip
	For complete details of Spring Data Solr, refer to their reference documentation.

Elastic Search is an open source, distributed, real-time search and analytics engine. Spring Boot offers basic auto-configuration for the Elasticsearch and abstractions on top of it provided by Spring Data Elasticsearch. There is a spring-boot-starter-data-elasticsearch ‘Starter POM’ for collecting the dependencies in a convenient way.

@Component
public class MyBean {

    private ElasticsearchTemplate template;

    @Autowired
    public MyBean(ElasticsearchTemplate template) {
        this.template = template;
    }

    // ...

}

29.5.2 Spring Data Elasticsearch repositories

Spring Data includes repository support for Elasticsearch. As with the JPA repositories discussed earlier, the basic principle is that queries are constructed for you automatically based on method names.

In fact, both Spring Data JPA and Spring Data Elasticsearch share the same common infrastructure; so you could take the JPA example from earlier and, assuming that City is now an Elasticsearch @Document class rather than a JPA @Entity, it will work in the same way.

	Tip
	For complete details of Spring Data Elasticsearch, refer to their reference documentation.

The javax.jms.ConnectionFactory interface provides a standard method of creating a javax.jms.Connection for interacting with a JMS broker. Although Spring needs a ConnectionFactory to work with JMS, you generally won’t need to use it directly yourself and you can instead rely on higher level messaging abstractions (see the relevant section of the Spring Framework reference documentation for details). Spring Boot also auto configures the necessary infrastructure to send and receive messages.

30.1.1 HornetQ support

Spring Boot can auto-configure a ConnectionFactory when it detects that HornetQ is available on the classpath. If the broker is present, an embedded broker is started and configured automatically (unless the mode property has been explicitly set). The supported modes are: embedded (to make explicit that an embedded broker is required and should lead to an error if the broker is not available in the classpath), and native to connect to a broker using the the netty transport protocol. When the latter is configured, Spring Boot configures a ConnectionFactory connecting to a broker running on the local machine with the default settings.

	Note
	If you are using spring-boot-starter-hornetq the necessary dependencies to connect to an existing HornetQ instance are provided, as well as the Spring infrastructure to integrate with JMS. Adding org.hornetq:hornetq-jms-server to your application allows you to use the embedded mode.

HornetQ configuration is controlled by external configuration properties in spring.hornetq.*. For example, you might declare the following section in application.properties:

spring.hornetq.mode=native
spring.hornetq.host=192.168.1.210
spring.hornetq.port=9876

When embedding the broker, you can chose if you want to enable persistence, and the list of destinations that should be made available. These can be specified as a comma-separated list to create them with the default options; or you can define bean(s) of type org.hornetq.jms.server.config.JMSQueueConfiguration or org.hornetq.jms.server.config.TopicConfiguration, for advanced queue and topic configurations respectively.

See HornetQProperties for more of the supported options.

No JNDI lookup is involved at all and destinations are resolved against their names, either using the ‘name’ attribute in the HornetQ configuration or the names provided through configuration.

spring.activemq.broker-url=tcp://192.168.1.210:9876
spring.activemq.user=admin
spring.activemq.password=secret

spring.jms.jndi-name=java:/MyConnectionFactory

30.1.4 Sending a message

Spring’s JmsTemplate is auto-configured and you can autowire it directly into your own beans:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jms.core.JmsTemplate;
import org.springframework.stereotype.Component;

@Component
public class MyBean {

    private final JmsTemplate jmsTemplate;

    @Autowired
    public MyBean(JmsTemplate jmsTemplate) {
        this.jmsTemplate = jmsTemplate;
    }

    // ...

}

	Note
	JmsMessagingTemplate (new in Spring 4.1) can be injected in a similar manner.

@Component
public class MyBean {

    @JmsListener(destination = "someQueue")
    public void processMessage(String content) {
        // ...
    }

}

Atomikos is a popular open source transaction manager which can be embedded into your Spring Boot application. You can use the spring-boot-starter-jta-atomikos Starter POM to pull in the appropriate Atomikos libraries. Spring Boot will auto-configure Atomikos and ensure that appropriate depends-on settings are applied to your Spring Beans for correct startup and shutdown ordering.

By default Atomikos transaction logs will be written to a transaction-logs folder in your application home directory (the directory in which your application jar file resides). You can customize this directory by setting a spring.jta.log-dir property in your application.properties file. Properties starting spring.jta. can also be used to customize the Atomikos UserTransactionServiceIml. See the AtomikosProperties javadoc for complete details.

Note

To ensure that multiple transaction managers can safely coordinate the same resource managers, each Atomikos instance must be configured with a unique ID. By default this ID is the IP address of the machine on which Atomikos is running. To ensure uniqueness in production, you should configure the spring.jta.transaction-manager-id property with a different value for each instance of your application.

Bitronix is another popular open source JTA transaction manager implementation. You can use the spring-boot-starter-jta-bitronix starter POM to add the appropriate Birtronix dependencies to your project. As with Atomikos, Spring Boot will automatically configure Bitronix and post-process your beans to ensure that startup and shutdown ordering is correct.

By default Bitronix transaction log files (part1.btm and part2.btm) will be written to a transaction-logs folder in your application home directory. You can customize this directory by using the spring.jta.log-dir property. Properties starting spring.jta. are also bound to the bitronix.tm.Configuration bean, allowing for complete customization. See the Bitronix documentation for details.

Note

To ensure that multiple transaction managers can safely coordinate the same resource managers, each Bitronix instance must be configured with a unique ID. By default this ID is the IP address of the machine on which Bitronix is running. To ensure uniqueness in production, you should configure the spring.jta.transaction-manager-id property with a different value for each instance of your application.

If you are packaging your Spring Boot application as a war or ear file and deploying it to a Java EE application server, you can use your application servers built-in transaction manager. Spring Boot will attempt to auto-configure a transaction manager by looking at common JNDI locations (java:comp/UserTransaction, java:comp/TransactionManager etc). If you are using a transaction service provided by your application server, you will generally also want to ensure that all resources are managed by the server and exposed over JNDI. Spring Boot will attempt to auto-configure JMS by looking for a ConnectionFactory at the JNDI path java:/JmsXA or java:/XAConnectionFactory and you can use the spring.datasource.jndi-name property to configure your DataSource.

When using JTA, the primary JMS ConnectionFactory bean will be XA aware and participate in distributed transactions. In some situations you might want to process certain JMS messages using a non-XA ConnectionFactory. For example, your JMS processing logic might take longer than the XA timeout.

If you want to use a non-XA ConnectionFactory you can inject the nonXaJmsConnectionFactory bean rather than the @Primary jmsConnectionFactory bean. For consistency the jmsConnectionFactory bean is also provided using the bean alias xaJmsConnectionFactory.

For example:

// Inject the primary (XA aware) ConnectionFactory
@Autowired
private ConnectionFactory defaultConnectionFactory;

// Inject the XA aware ConnectionFactory (uses the alias and injects the same as above)
@Autowired
@Qualifier("xaJmsConnectionFactory")
private ConnectionFactory xaConnectionFactory;

// Inject the non-XA aware ConnectionFactory
@Autowired
@Qualifier("nonXaJmsConnectionFactory")
private ConnectionFactory nonXaConnectionFactory;

The XAConnectionFactoryWrapper and XADataSourceWrapper interfaces can be used to support alternative embedded transaction managers. The interfaces are responsible for wrapping XAConnectionFactory and XADataSource beans and exposing them as regular ConnectionFactory and DataSource beans which will transparently enroll in the distributed transaction. DataSource and JMS auto-configuration will use JTA variants as long as you have a JtaTransactionManager bean and appropriate XA wrapper beans registered within your ApplicationContext

The BitronixXAConnectionFactoryWrapper and BitronixXADataSourceWrapper provide good examples of how to write XA wrappers.

If you use the spring-boot-starter-test ‘Starter POM’ (in the test scope), you will find the following provided libraries:

These are common libraries that we generally find useful when writing tests. You are free to add additional test dependencies of your own if these don’t suit your needs.

One of the major advantages of dependency injection is that it should make your code easier to unit test. You can simply instantiate objects 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 actually involved in the process). It’s 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 just such integration testing. You can declare a dependency directly to org.springframework:spring-test or use the spring-boot-starter-test ‘Starter POM’ 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.

A Spring Boot application is just 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. One thing to watch out for though is that the external properties, logging and other features of Spring Boot are only installed in the context by default if you use SpringApplication to create it.

Spring Boot provides a @SpringApplicationConfiguration annotation as an alternative to the standard spring-test @ContextConfiguration annotation. If you use @SpringApplicationConfiguration to configure the ApplicationContext used in your tests, it will be created via SpringApplication and you will get the additional Spring Boot features.

For example:

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = SampleDataJpaApplication.class)
public class CityRepositoryIntegrationTests {

    @Autowired
    CityRepository repository;

    // ...

}

	Tip
	The context loader guesses whether you want to test a web application or not (e.g. with MockMVC) by looking for the @WebAppConfiguration annotation. (MockMVC and @WebAppConfiguration are part of spring-test).

If you want a web application to start up and listen on its normal port, so you can test it with HTTP (e.g. using RestTemplate), annotate your test class (or one of its superclasses) with @IntegrationTest. This can be very useful because it means you can test the full stack of your application, but also inject its components into the test class and use them to assert the internal state of the application after an HTTP interaction. For example:

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = SampleDataJpaApplication.class)
@WebAppConfiguration
@IntegrationTest
public class CityRepositoryIntegrationTests {

    @Autowired
    CityRepository repository;

    RestTemplate restTemplate = new TestRestTemplate();

    // ... interact with the running server

}

	Note
	Spring’s test framework will cache application contexts between tests. Therefore, as long as your tests share the same configuration, the time consuming process of starting and stopping the server will only happen once, regardless of the number of tests that actually run.

To change the port you can add environment properties to @IntegrationTest as colon- or equals-separated name-value pairs, e.g. @IntegrationTest("server.port:9000"). Additionally you can set the server.port and management.port properties to 0 in order to run your integration tests using random ports. For example:

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = MyApplication.class)
@WebAppConfiguration
@IntegrationTest({"server.port=0", "management.port=0"})
public class SomeIntegrationTests {

    // ...

}

See Section 64.4, “Discover the HTTP port at runtime” for a description of how you can discover the actual port that was allocated for the duration of the tests.

35.3.1 Using Spock to test Spring Boot applications

If you wish to use Spock to test a Spring Boot application you should add a dependency on Spock’s spock-spring module to your application’s build. spock-spring integrates Spring’s test framework into Spock.

Please note that you cannot use the @SpringApplicationConfiguration annotation that was described above as Spock does not find the @ContextConfiguration meta-annotation. To work around this limitation, you should use the @ContextConfiguration annotation directly and configure it to use the Spring Boot specific context loader:

@ContextConfiguration(loader = SpringApplicationContextLoader.class)
class ExampleSpec extends Specification {

    // ...

}

	Note
	The annotations described above can be used with Spock, i.e. you can annotate your Specification with @IntegrationTest and @WebAppConfiguration to suit the needs of your tests.

A few test utility classes are packaged as part of spring-boot that are generally useful when testing your application.

@ContextConfiguration(classes = Config.class,
    initializers = ConfigFileApplicationContextInitializer.class)

EnvironmentTestUtils.addEnvironment(env, "org=Spring", "name=Boot");

import org.junit.Rule;
import org.junit.Test;
import org.springframework.boot.test.OutputCapture;

import static org.hamcrest.Matchers.*;
import static org.junit.Assert.*;

public class MyTest {

	@Rule
	public OutputCapture capture = new OutputCapture();

	@Test
	public void testName() throws Exception {
		System.out.println("Hello World!");
		assertThat(capture.toString(), containsString("World"));
	}

}

public class MyTest {

	RestTemplate template = new TestRestTemplate();

	@Test
	public void testRequest() throws Exception {
		HttpHeaders headers = template.getForEntity("http://myhost.com", String.class).getHeaders();
		assertThat(headers.getLocation().toString(), containsString("myotherhost"));
	}

}

Under the hood, auto-configuration is implemented with 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 only applies 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 @Configuration classes that we provide (see the META-INF/spring.factories file).

Spring Boot checks for the presence of a META-INF/spring.factories file within your published jar. The file should list your configuration classes under the EnableAutoConfiguration key.

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.mycorp.libx.autoconfigure.LibXAutoConfiguration,\
com.mycorp.libx.autoconfigure.LibXWebAutoConfiguration

You can use the @AutoConfigureAfter or @AutoConfigureBefore annotations if your configuration needs to be applied in a specific order. For example, if you provide web-specific configuration, your class may need to be applied after WebMvcAutoConfiguration.

You almost always want to include one or more @Condition annotations on your auto-configuration class. The @ConditionalOnMissingBean 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.

36.3.2 Bean conditions

The @ConditionalOnBean and @ConditionalOnMissingBean annotations allow configurations to be skipped 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 allows you to limit the ApplicationContext hierarchy that should be considered when searching for beans.

	Note
	@Conditional annotations are processed when @Configuration classes are parsed. Auto-configure @Configuration is always parsed last (after any user defined beans), however, if you are using these annotations on regular @Configuration classes, care must be taken not to refer to bean definitions that have not yet been created.

Endpoints can be customized using Spring properties. You can change if an endpoint is enabled, if it is considered sensitive and even its id.

For example, here is an application.properties that changes the sensitivity and id of the beans endpoint and also enables shutdown.

endpoints.beans.id=springbeans
endpoints.beans.sensitive=false
endpoints.shutdown.enabled=true

	Note
	The prefix ‟endpoints + . + name” is used to uniquely identify the endpoint that is being configured.

By default, all endpoints except for shutdown are enabled. If you prefer to specifically “opt-in” endpoint enablement you can use the endpoints.enabled property. For example, the following will disable all endpoints except for info:

endpoints.enabled=false
endpoints.info.enabled=true

Health information can be used to check the status of your running application. It is often used by monitoring software to alert someone if a production system goes down. The default information exposed by the health endpoint depends on how it is accessed. For an insecure unauthenticated connection a simple ‘status’ message is returned, for a secure or authenticated connection additional details are also displayed (see Section 41.6, “HTTP Health endpoint access restrictions” for HTTP details).

Health information is collected from all HealthIndicator beans defined in your ApplicationContext. Spring Boot includes a number of auto-configured HealthIndicators and you can also write your own.

Information returned by HealthIndicators is often somewhat sensitive in nature. For example, you probably don’t want to publish details of your database server to the world. For this reason, by default, only the health status is exposed over an unauthenticated HTTP connection. If you are happy for complete health information to always be exposed you can set endpoints.health.sensitive to false.

Health responses are also cached to prevent “denial of service” attacks. Use the endpoints.health.time-to-live property if you want to change the default cache period of 1000 milliseconds.

import org.springframework.boot.actuate.health.HealthIndicator;
import org.springframework.stereotype.Component;

@Component
public class MyHealth implements HealthIndicator {

    @Override
    public Health health() {
        int errorCode = check(); // perform some specific health check
        if (errorCode != 0) {
            return Health.down().withDetail("Error Code", errorCode);
        }
        return Health.up();
    }

}

management.health.status.order: DOWN, OUT_OF_SERVICE, UNKNOWN, UP

You can customize the data exposed by the info endpoint by setting info.* Spring properties. All Environment properties under the info key will be automatically exposed. For example, you could add the following to your application.properties:

info.app.name=MyService
info.app.description=My awesome service
info.app.version=1.0.0

40.4.1 Automatically expand info properties at build time

Rather than hardcoding some properties that are also specified in your project’s build configuration, you can automatically expand info properties using the existing build configuration instead. This is possible in both Maven and Gradle.

Automatic property expansion using Maven

You can automatically expand info properties from the Maven project using resource filtering. If you use the spring-boot-starter-parent you can then refer to your Maven ‘project properties’ via @..@ placeholders, e.g.

project.artifactId=myproject
project.name=Demo
project.version=X.X.X.X
project.description=Demo project for info endpoint
info.build.artifact[email protected]@
info.build.name[email protected]@
info.build.description[email protected]@
info.build.version[email protected]@

	Note
	In the above example we used project.* to set some values to be used as fallbacks if the Maven resource filtering has not been switched on for some reason.

	Note
	If you don’t use the starter parent, in your pom.xml you need (inside the <build/> element):

<resources>
    <resource>
        <directory>src/main/resources</directory>
        <filtering>true</filtering>
    </resource>
</resources>

and (inside <plugins/>):

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-resources-plugin</artifactId>
    <version>2.6</version>
    <configuration>
        <delimiters>
            <delimiter>@</delimiter>
        </delimiters>
    </configuration>
</plugin>

Automatic property expansion using Gradle

You can automatically expand info properties from the Gradle project by configuring the Java plugin’s processResources task to do so:

processResources {
    expand(project.properties)
}

You can then refer to your Gradle project’s properties via placeholders, e.g.

info.build.name=${name}
info.build.description=${description}
info.build.version=${version}

<build>
    <plugins>
        <plugin>
            <groupId>pl.project13.maven</groupId>
            <artifactId>git-commit-id-plugin</artifactId>
        </plugin>
    </plugins>
</build>

If you add ‘Spring Security’ to your project, all sensitive endpoints exposed over HTTP will be protected. By default ‘basic’ authentication will be used with the username user and a generated password (which is printed on the console when the application starts).

	Tip
	Generated passwords are logged as the application starts. Search for ‘Using default security password’.

You can use Spring properties to change the username and password and to change the security role required to access the endpoints. For example, you might set the following in your application.properties:

security.user.name=admin
security.user.password=secret
management.security.role=SUPERUSER

	Tip
	If you don’t use Spring Security and your HTTP endpoints are exposed publicly, you should carefully consider which endpoints you enable. See Section 40.1, “Customizing endpoints” for details of how you can set endpoints.enabled to false then “opt-in” only specific endpoints.

Sometimes it is useful to group all management endpoints under a single path. For example, your application might already use /info for another purpose. You can use the management.contextPath property to set a prefix for your management endpoint:

management.context-path=/manage

The application.properties example above will change the endpoint from /{id} to /manage/{id} (e.g. /manage/info).

Exposing management endpoints using the default HTTP port is a sensible choice for cloud based deployments. If, however, your application runs inside your own data center you may prefer to expose endpoints using a different HTTP port.

The management.port property can be used to change the HTTP port.

management.port=8081

Since your management port is often protected by a firewall, and not exposed to the public you might not need security on the management endpoints, even if your main application is secure. In that case you will have Spring Security on the classpath, and you can disable management security like this:

management.security.enabled=false

(If you don’t have Spring Security on the classpath then there is no need to explicitly disable the management security in this way, and it might even break the application.)

You can customize the address that the management endpoints are available on by setting the management.address property. This can be useful if you want to listen only on an internal or ops-facing network, or to only listen for connections from localhost.

	Note
	You can only listen on a different address if the port is different to the main server port.

Here is an example application.properties that will not allow remote management connections:

management.port=8081
management.address=127.0.0.1

If you don’t want to expose endpoints over HTTP you can set the management port to -1:

management.port=-1

The information exposed by the health endpoint varies depending on whether or not it’s accessed anonymously. By default, when accessed anonymously, any details about the server’s health are hidden and the endpoint will simply indicate whether or not the server is up or down. Furthermore, when accessed anonymously, the response is cached for a configurable period to prevent the endpoint being used in a denial of service attack. The endpoints.health.time-to-live property is used to configure the caching period in milliseconds. It defaults to 1000, i.e. one second.

The above-described restrictions can be disabled, thereby allowing anonymous users full access to the health endpoint. To do so, set endpoints.health.sensitive to false.

The name of the MBean is usually generated from the id of the endpoint. For example the health endpoint is exposed as org.springframework.boot/Endpoint/HealthEndpoint.

If your application contains more than one Spring ApplicationContext you may find that names clash. To solve this problem you can set the endpoints.jmx.uniqueNames property to true so that MBean names are always unique.

You can also customize the JMX domain under which endpoints are exposed. Here is an example application.properties:

endpoints.jmx.domain=myapp
endpoints.jmx.uniqueNames=true

If you don’t want to expose endpoints over JMX you can set the spring.jmx.enabled property to false:

spring.jmx.enabled=false

Jolokia is a JMX-HTTP bridge giving an alternative method of accessing JMX beans. To use Jolokia, simply include a dependency to org.jolokia:jolokia-core. For example, using Maven you would add the following:

<dependency>
    <groupId>org.jolokia</groupId>
    <artifactId>jolokia-core</artifactId>
 </dependency>

Jolokia can then be accessed using /jolokia on your management HTTP server.

jolokia.config.debug=true

endpoints.jolokia.enabled=false

By default the remote shell will listen for connections on port 2000. The default user is user and the default password will be randomly generated and displayed in the log output. If your application is using Spring Security, the shell will use the same configuration by default. If not, a simple authentication will be applied and you should see a message like this:

Using default password for shell access: ec03e16c-4cf4-49ee-b745-7c8255c1dd7e

Linux and OSX users can use ssh to connect to the remote shell, Windows users can download and install PuTTY.

$ ssh -p 2000 user@localhost

user@localhost's password:
  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::  (v1.2.0.RELEASE) on myhost

Type help for a list of commands. Spring boot provides metrics, beans, autoconfig and endpoint commands.

The remote shell can be extended in a number of interesting ways.

43.2.1 Remote shell commands

You can write additional shell commands using Groovy or Java (see the CRaSH documentation for details). By default Spring Boot will search for commands in the following locations:

• classpath*:/commands/**
• classpath*:/crash/commands/**

	Tip
	You can change the search path by settings a shell.commandPathPatterns property.

Here is a simple ‘hello world’ command that could be loaded from src/main/resources/commands/hello.groovy

package commands

import org.crsh.cli.Usage
import org.crsh.cli.Command

class hello {

    @Usage("Say Hello")
    @Command
    def main(InvocationContext context) {
        return "Hello"
    }

}

Spring Boot adds some additional attributes to InvocationContext that you can access from your command:

Attribute Name	Description
spring.boot.version	The version of Spring Boot
spring.version	The version of the core Spring Framework
spring.beanfactory	Access to the Spring BeanFactory
spring.environment	Access to the Spring Environment

The following system metrics are exposed by Spring Boot:

The following metrics are exposed for each supported DataSource defined in your application:

All data source metrics share the datasource. prefix. The prefix is further qualified for each data source:

It is possible to override part or all of those defaults by registering a bean with a customized version of DataSourcePublicMetrics. By default, Spring Boot provides metadata for all supported datasources; you can add additional DataSourcePoolMetadataProvider beans if your favorite data source isn’t supported out of the box. See DataSourcePoolMetadataProvidersConfiguration for examples.

If you are using Tomcat as your embedded servlet container, session metrics will automatically be exposed. The httpsessions.active and httpsessions.max keys provide the number of active and maximum sessions.

To record your own metrics inject a CounterService and/or GaugeService into your bean. The CounterService exposes increment, decrement and reset methods; the GaugeService provides a submit method.

Here is a simple example that counts the number of times that a method is invoked:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.actuate.metrics.CounterService;
import org.springframework.stereotype.Service;

@Service
public class MyService {

    private final CounterService counterService;

    @Autowired
    public MyService(CounterService counterService) {
        this.counterService = counterService;
    }

    public void exampleMethod() {
        this.counterService.increment("services.system.myservice.invoked");
    }

}

	Tip
	You can use any string as a metric name but you should follow guidelines of your chosen store/graphing technology. Some good guidelines for Graphite are available on Matt Aimonetti’s Blog.

To add additional metrics that are computed every time the metrics endpoint is invoked, simply register additional PublicMetrics implementation bean(s). By default, all such beans are gathered by the endpoint. You can easily change that by defining your own MetricsEndpoint.

Metric service implementations are usually bound to a MetricRepository. A MetricRepository is responsible for storing and retrieving metric information. Spring Boot provides an InMemoryMetricRepository and a RedisMetricRepository out of the box (the in-memory repository is the default) but you can also write your own. The MetricRepository interface is actually composed of higher level MetricReader and MetricWriter interfaces. For full details refer to the Javadoc.

There’s nothing to stop you hooking a MetricRepository with back-end storage directly into your app, but we recommend using the default InMemoryMetricRepository (possibly with a custom Map instance if you are worried about heap usage) and populating a back-end repository through a scheduled export job. In that way you get some buffering in memory of the metric values and you can reduce the network chatter by exporting less frequently or in batches. Spring Boot provides an Exporter interface and a few basic implementations for you to get started with that.

User of the Dropwizard ‘Metrics’ library will automatically find that Spring Boot metrics are published to com.codahale.metrics.MetricRegistry. A default com.codahale.metrics.MetricRegistry Spring bean will be created when you declare a dependency to the io.dropwizard.metrics:metrics-core library; you can also register you own @Bean instance if you need customizations. Metrics from the MetricRegistry are also automatically exposed via the /metrics endpoint

Users can create Dropwizard metrics by prefixing their metric names with the appropriate type (e.g. histogram.*, meter.*).

If the ‘Spring Messaging’ jar is on your classpath a MessageChannel called metricsChannel is automatically created (unless one already exists). All metric update events are additionally published as ‘messages’ on that channel. Additional analysis or actions can be taken by clients subscribing to that channel.

If you need to trace additional events you can inject a TraceRepository into your Spring Beans. The add method accepts a single Map structure that will be converted to JSON and logged.

By default an InMemoryTraceRepository will be used that stores the last 100 events. You can define your own instance of the InMemoryTraceRepository bean if you need to expand the capacity. You can also create your own alternative TraceRepository implementation if needed.

In META-INF/spring.factories file you have to activate the listener(s):

org.springframework.context.ApplicationListener=\
org.springframework.boot.actuate.system.ApplicationPidFileWriter,
org.springframework.boot.actuate.system.EmbeddedServerPortFileWriter

You can also activate a listener by invoking the SpringApplication.addListeners(…​) method and passing the appropriate Writer object. This method also allows you to customize the file name and path via the Writer constructor.

By default, metadata about the running application as well as service connection information is exposed to the application as environment variables (for example: $VCAP_SERVICES). This architecture decision is due to Cloud Foundry’s polyglot (any language and platform can be supported as a buildpack) nature; process-scoped environment variables are language agnostic.

Environment variables don’t always make for the easiest API so Spring Boot automatically extracts them and flattens the data into properties that can be accessed through Spring’s Environment abstraction:

@Component
class MyBean implements EnvironmentAware {

    private String instanceId;

    @Override
    public void setEnvironment(Environment environment) {
        this.instanceId = environment.getProperty("vcap.application.instance_id");
    }

    // ...

}

All Cloud Foundry properties are prefixed with vcap. You can use vcap properties to access application information (such as the public URL of the application) and service information (such as database credentials). See VcapApplicationListener Javdoc for complete details.

	Tip
	The Spring Cloud Connectors project is a better fit for tasks such as configuring a DataSource. Spring Boot includes auto-configuration support and a spring-boot-starter-cloud-connectors starter POM.

You can compile and run Groovy source code using the run command. The Spring Boot CLI is completely self-contained so you don’t need any external Groovy installation.

Here is an example “hello world” web application written in Groovy:

hello.groovy. 

@RestController
class WebApplication {

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

}

To compile and run the application type:

$ spring run hello.groovy

To pass command line arguments to the application, you need to use a -- to separate them from the “spring” command arguments, e.g.

$ spring run hello.groovy -- --server.port=9000

To set JVM command line arguments you can use the JAVA_OPTS environment variable, e.g.

$ JAVA_OPTS=-Xmx1024m spring run hello.groovy

55.1.1 Deduced “grab” dependencies

Standard Groovy includes a @Grab annotation which allows you to declare dependencies on a third-party libraries. This useful technique allows Groovy to download jars in the same way as Maven or Gradle would, but without requiring you to use a build tool.

Spring Boot extends this technique further, and will attempt to deduce which libraries to “grab” based on your code. For example, since the WebApplication code above uses @RestController annotations, “Tomcat” and “Spring MVC” will be grabbed.

The following items are used as “grab hints”:

Items	Grabs
JdbcTemplate, NamedParameterJdbcTemplate, DataSource	JDBC Application.
@EnableJms	JMS Application.
@EnableCaching	Caching abstraction.
@Test	JUnit.
@EnableRabbit	RabbitMQ.
@EnableReactor	Project Reactor.
extends Specification	Spock test.
@EnableBatchProcessing	Spring Batch.
@MessageEndpoint @EnableIntegrationPatterns	Spring Integration.
@EnableDeviceResolver	Spring Mobile.
@Controller @RestController @EnableWebMvc	Spring MVC + Embedded Tomcat.
@EnableWebSecurity	Spring Security.
@EnableTransactionManagement	Spring Transaction Management.

	Tip
	See subclasses of CompilerAutoConfiguration in the Spring Boot CLI source code to understand exactly how customizations are applied.

55.1.3 Default import statements

To help reduce the size of your Groovy code, several import statements are automatically included. Notice how the example above refers to @Component, @RestController and @RequestMapping without needing to use fully-qualified names or import statements.

	Tip
	Many Spring annotations will work without using import statements. Try running your application to see what fails before adding imports.

`@GrabMetadata("com.example.custom-versions:1.0.0")`

`@GrabMetadata(["com.example.custom-versions:1.0.0",
        "com.example.more-versions:1.0.0"])`

The test command allows you to compile and run tests for your application. Typical usage looks like this:

$ spring test app.groovy tests.groovy
Total: 1, Success: 1, : Failures: 0
Passed? true

In this example, tests.groovy contains JUnit @Test methods or Spock Specification classes. All the common framework annotations and static methods should be available to you without having to import them.

Here is the tests.groovy file that we used above (with a JUnit test):

class ApplicationTests {

    @Test
    void homeSaysHello() {
        assertEquals("Hello World!", new WebApplication().home())
    }

}

	Tip
	If you have more than one test source files, you might prefer to organize them into a test directory.

You can use “shell globbing” with all commands that accept file input. This allows you to easily use multiple files from a single directory, e.g.

$ spring run *.groovy

This technique can also be useful if you want to segregate your “test” or “spec” code from the main application code:

$ spring test app/*.groovy test/*.groovy

You can use the jar command to package your application into a self-contained executable jar file. For example:

$ spring jar my-app.jar *.groovy

The resulting jar will contain the classes produced by compiling the application and all of the application’s dependencies so that it can then be run using java -jar. The jar file will also contain entries from the application’s classpath. You can add explicit paths to the jar using --include and --exclude (both are comma-separated, and both accept prefixes to the values “+” and “-” to signify that they should be removed from the defaults). The default includes are

public/**, resources/**, static/**, templates/**, META-INF/**, *

and the default excludes are

.*, repository/**, build/**, target/**, **/*.jar, **/*.groovy