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).

9.1.1 Maven installation

Spring Boot is compatible with Apache Maven 3.0 or above. If you don’t already have Maven installed you can follow the instructions at http://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>1.0.2.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>

buildscript {
    repositories {
        mavenCentral()
        maven { url "http://repo.spring.io/snapshot" }
        maven { url "http://repo.spring.io/milestone" }
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:1.0.2.RELEASE")
    }
}

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

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

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

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

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 v1.0.2.RELEASE

$ gvm install springboot dev /path/to/spring-boot/spring-boot-cli/target/spring-boot-cli-1.0.2.RELEASE-bin/spring-1.0.2.RELEASE/
$ gvm use springboot dev
$ spring --version
Spring CLI v1.0.2.RELEASE

$ gvm ls springboot

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

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

9.2.3 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.

9.2.4 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.

9.2.5 Quick start Spring CLI example

Here’s a really simple web application that you can use to test you 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 http://localhost:8080 in your favorite web browser and you should see the following output:

Hello World!

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 you 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>1.0.2.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
[INFO] +- junit:junit:jar:4.11:test
[INFO] |  \- org.hamcrest:hamcrest-core:jar:1.3:test
[INFO] +- org.mockito:mockito-core:jar:1.9.5:test
[INFO] |  \- org.objenesis:objenesis:jar:1.0:test
[INFO] \- org.hamcrest:hamcrest-library:jar:1.3:test

The mvn dependency:tree command prints tree representation of your project dependencies. You can see that spring-boot-starter-parent has already provided some useful test dependencies. 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 though the important parts.

10.3.1 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 ::  (v1.0.2.RELEASE)
....... . . .
....... . . . (log output here)
....... . . .
........ Started Example in 2.222 seconds (JVM running for 6.514)

If you open a web browser to http://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>

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:1.0.2.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 ::  (v1.0.2.RELEASE)
....... . . .
....... . . . (log output here)
....... . . .
........ Started Example in 3.236 seconds (JVM running for 3.764)

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:

12.1.1 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>1.0.2.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-starter-parent</artifactId>
            <version>1.0.2.RELEASE</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

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

12.1.4 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
	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 { mavenCentral() }
dependencies {
    compile("org.springframework.boot:spring-boot-starter-web:1.0.2.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 { mavenCentral() }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:1.0.2.RELEASE")
    }
}

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

repositories { mavenCentral() }
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 65.3, “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 or @EntityScan 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.

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={EmbeddedDatabaseConfiguration.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 meta-data 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 Relauch 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

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

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.

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 21, 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.

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 profiles 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 55.3, “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.

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 {
}

21.6.2 @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

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 21.3, “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 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.

By default, log files are written to spring.log in your temp directory and rotate at 10 Mb. You can easily customize the output folder by setting the logging.path property (for example in your application.properties). It is also possible to change the filename using a logging.file property.

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

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.

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 http://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);
    }

}

24.1.3 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 ServeltContext. 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.

24.1.4 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 Thymeleaf templating engine. Thymeleaf is an XML/XHTML/HTML5 template engine that can work both in web and non-web environments. It allows you to create natural templates that can be correctly displayed by browsers and therefore work also as static prototypes. Thymeleaf 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.

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

24.2.2 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 or JettyEmbeddedServletContainerFactory 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.

26.1.1 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.

26.1.2 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 commons-dbcp is available we will use that, but we don’t recommend it in production.

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.driverClassName=com.mysql.jdbc.Driver

See AbstractDataSourceConfiguration for more of the supported options.

	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’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 http://spring.io and read the Spring Data JPA and Hibernate reference documentation.

26.3.1 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) 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 59.3, “Separate @Entity definitions from Spring configuration” how-to.

26.3.2 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) 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.

26.3.3 Creating and dropping JPA databases

By default JPA database 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). Alternatively, spring.jpa.generate-ddl=false switches off all DDL generation.

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”.

27.1.1 Connecting to a MongoDB database

You can inject an auto-configured com.mongodb.Mongo instance as you would any other Spring Bean. By default the instance will attempt to connect to a MongoDB server using the URL mongodb://localhost/test:

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

import com.mongodb.Mongo;

@Component
public class MyBean {

    private final Mongo mongo;

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

    // ...

}

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.

You can also declare your own Mongo @Bean 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;
    }

    // ...

}

27.1.3 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.

If you extend your Maven project from the spring-boot-starter-parent POM, or 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)
@WebApplication
@IntegrationTest
public class CityRepositoryIntegrationTests {

    @Autowired
    CityRepository repository;

    RestTemplate restTemplate = new TestRestTemplate();

    // ... interact with the running server

}

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").

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.

29.3.2 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.

The default information exposed by the health endpoint is a simple “OK” message. It is often useful to perform some additional health checks, for example you might check that a database connection works, or that a remote REST endpoint is functioning.

To provide custom health information you can register a Spring bean that implements the HealthIndicator interface.

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

@Component
public class MyHealth implements HealthIndicator<String> {

    @Override
    public String health() {
        // perform some specific health check
        return ...
    }

}

Spring Boot also provides a SimpleHealthIndicator implementation that attempts a simple database test.

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

If you are using Maven, you can automatically expand info properties from the Maven project using resource filtering. In your pom.xml you have (inside the <build/> element):

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

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

	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.

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

If you use “Spring Security” sensitive endpoints will be exposed over HTTP, but also 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 password for application endpoints”.

You can use Spring properties to change the username and passsword 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

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 manangement 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 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, 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 ::  (v1.0.2.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.

35.2.1 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

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.

Metric service implementations are usually bound to a MetricRepository. A MetricRepository is responsible for storing and retrieving metric information. Spring Boot provides an InMemoryMessageRespository 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.

User of the Coda Hale “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 com.codahale.metrics:metrics-core library; you can also register you own @Bean instance if you need customizations.

Users can create Coda Hale 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:

org.springframework.context.ApplicationListener=\
org.springframework.boot.actuate.system.ApplicationPidListener

You can also activate this listener by invoking SpringApplication.addListeners(...) method and passing ApplicationPidListener object. You can also customize file name and path through constructor.

By default, meta-data 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 project is a better fit for tasks such as configuring a DataSource; it also lets you use Spring Cloud with Heroku.

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:

@RestController
class WebApplication {

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

}

47.1.1 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.
@EnableJmsMessaging	JMS Application.
@Test	JUnit.
@EnableRabbitMessaging	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.

47.1.2 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.

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 test.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.

See the output of spring help jar for more information.

Spring Boot includes command-line completion scripts for BASH and zsh shells. If you don’t use either of these shells (perhaps you are a Windows user) then you can use the shell command to launch an integrated shell.

$ spring shell
Spring Boot (v1.0.2.RELEASE)
Hit TAB to complete. Type 'help' and hit RETURN for help, and 'exit' to quit.

From inside the embedded shell you can run other commands directly:

$ version
Spring CLI v1.0.2.RELEASE

The embedded shell supports ANSI color output as well as tab completion. If you need to run a native command you can use the $ prefix. Hitting ctrl-c will exit the embedded shell.

To use the Spring Boot Maven Plugin simply include the appropriate XML in the plugins section of your pom.xml

<?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>
    <!-- ... -->
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>1.0.2.RELEASE</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

This configuration will repackage a jar or war that is built during the package phase of the Maven lifecycle. The following example shows both the repackaged jar, as well as the original jar, in the target directory:

$ mvn package
$ ls target/*.jar
target/myproject-1.0.0.jar target/myproject-1.0.0.jar.original

If you don’t include the <execution/> configuration as above, you can run the plugin on its own (but only if the package goal is used as well). For example:

$ mvn package spring-boot:repackage
$ ls target/*.jar
target/myproject-1.0.0.jar target/myproject-1.0.0.jar.original

If you are using a milestone or snapshot release you will also need to add appropriate pluginRepository elements:

<pluginRepositories>
    <pluginRepository>
        <id>spring-snapshots</id>
        <url>http://repo.spring.io/snapshot</url>
    </pluginRepository>
    <pluginRepository>
        <id>spring-milestones</id>
        <url>http://repo.spring.io/milestone</url>
    </pluginRepository>
</pluginRepositories>

Once spring-boot-maven-plugin has been included in your pom.xml it will automatically attempt to rewrite archives to make them executable using the spring-boot:repackage goal. You should configure your project to build a jar or war (as appropriate) using the usual packaging element:

<?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">
    <!-- ... -->
    <packaging>jar</packaging>
    <!-- ... -->
</project>

Your existing archive will be enhanced by Spring Boot during the package phase. The main class that you want to launch can either be specified using a configuration option, or by adding a Main-Class attribute to the manifest in the usual way. If you don’t specify a main class the plugin will search for a class with a public static void main(String[] args) method.

To build and run a project artifact, you can type the following:

$ mvn package
$ java -jar target/mymodule-0.0.1-SNAPSHOT.jar

To build a war file that is both executable and deployable into an external container you need to mark the embedded container dependencies as “provided”, e.g:

<?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">
    <!-- ... -->
    <packaging>war</packaging>
    <!-- ... -->
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
            <scope>provided</scope>
        </dependency>
        <!-- ... -->
    </dependencies>
</project>

The following configuration options are available for the spring-boot:repackage goal:

50.3.2 Optional parameters

Name	Description
classifier	Classifier to add to the generated artifact. If given, the artifact will be attached. If this is not given, it will merely be written to the output directory according to the finalName. Attaching the artifact allows to deploy it alongside to the original one, see the maven documentation for more details
mainClass	The name of the main class. If not specified will search for a single compiled class that contains a main method.
layout	The type of archive (which corresponds to how the dependencies are laid out inside it). Defaults to a guess based on the archive type.

The plugin rewrites your manifest, and in particular it manages the Main-Class and Start-Class entries, so if the defaults don’t work you have to configure those there (not in the jar plugin). The Main-Class in the manifest is actually controlled by the layout property of the boot plugin, e.g.

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <version>1.0.2.RELEASE</version>
    <configuration>
        <mainClass>${start-class}</mainClass>
        <layout>ZIP</layout>
    </configuration>
    <executions>
        <execution>
            <goals>
                <goal>repackage</goal>
            </goals>
        </execution>
    </executions>
</plugin>

The layout property defaults to a guess based on the archive type (jar or war). For the PropertiesLauncher the layout is “ZIP” (even though the output might be a jar file).

	Tip
	The executable jar format is described in the appendix.

The Spring Boot Maven Plugin includes a run goal which can be used to launch your application from the command line. Type the following from the root of your Maven project:

$ mvn spring-boot:run

By default, any src/main/resources folder will be added to the application classpath when you run via the maven plugin. This allows hot refreshing of resources which can be very useful when developing web applications. For example, you can work on HTML, CSS or JavaScipt files and see your changes immediately without recompiling your application. It is also a helpful way of allowing your front end developers to work without needing to download and install a Java IDE.

The following configuration options are available for the spring-boot:run goal:

To use the Spring Boot Gradle Plugin simply include a buildscript dependency and apply the spring-boot plugin:

buildscript {
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:1.0.2.RELEASE")
    }
}
apply plugin: 'spring-boot'

If you are using a milestone or snapshot release you will also need to add appropriate repositories reference:

buildscript {
    repositories {
        maven.url "http://repo.spring.io/snapshot"
        maven.url "http://repo.spring.io/milestone"
    }
    // ...
}

The spring-boot plugin will register a custom Gradle ResolutionStrategy with your build that allows you to omit version numbers when declaring dependencies to “blessed” artifacts. All artifacts with a org.springframework.boot group ID, and any of the artifacts declared in the managementDependencies section of the spring-dependencies POM can have their version number resolved automatically.

Simply declare dependencies in the usual way, but leave the version number empty:

dependencies {
    compile("org.springframework.boot:spring-boot-starter-web")
    compile("org.thymeleaf:thymeleaf-spring4")
    compile("nz.net.ultraq.thymeleaf:thymeleaf-layout-dialect")
}

	Note
	The version of the spring-boot gradle plugin that you declare determines the actual versions of the “blessed” dependencies (this ensures that builds are always repeatable). You should always set the version of the spring-boot gradle plugin to the actual Spring Boot version that you wish to use.

Once the spring-boot plugin has been applied to your project it will automatically attempt to rewrite archives to make them executable using the bootRepackage task. You should configure your project to build a jar or war (as appropriate) in the usual way.

The main class that you want to launch can either be specified using a configuration option, or by adding a Main-Class attribute to the manifest. If you don’t specify a main class the plugin will search for a class with a public static void main(String[] args) method.

To build and run a project artifact, you can type the following:

$ gradle build
$ java -jar build/libs/mymodule-0.0.1-SNAPSHOT.jar

To build a war file that is both executable and deployable into an external container, you need to mark the embedded container dependencies as belonging to a configuration named "providedRuntime", e.g:

...
apply plugin: 'war'

war {
    baseName = 'myapp'
    version =  '0.5.0'
}

repositories {
    mavenCentral()
    maven { url "http://repo.spring.io/libs-snapshot" }
}

configurations {
    providedRuntime
}

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

To run a project in place without building a jar first you can use the "bootRun" task:

$ gradle bootRun

Running this way makes your static classpath resources (i.e. in src/main/resources by default) reloadable in the live application, which can be helpful at development time.

The gradle plugin automatically extends your build script DSL with a springBoot element for configuration. Simply set the appropriate properties as you would with any other Gradle extension (see below for a list of configuration options):

springBoot {
    backupSource = false
}

Sometimes it may be more appropriate to not package default dependencies resolved from compile, runtime and provided scopes. If the created executable jar file is intended to be run as it is, you need to have all dependencies nested inside it; however, if the plan is to explode a jar file and run the main class manually, you may already have some of the libraries available via CLASSPATH. This is a situation where you can repackage your jar with a different set of dependencies.

Using a custom configuration will automatically disable dependency resolving from compile, runtime and provided scopes. Custom configuration can be either defined globally (inside the springBoot section) or per task.

task clientJar(type: Jar) {
    appendix = 'client'
    from sourceSets.main.output
    exclude('**/*Something*')
}

task clientBoot(type: BootRepackage, dependsOn: clientJar) {
    withJarTask = clientJar
    customConfiguration = "mycustomconfiguration"
}

In above example, we created a new clientJar Jar task to package a customized file set from your compiled sources. Then we created a new clientBoot BootRepackage task and instructed it to work with only clientJar task and mycustomconfiguration.

configurations {
    mycustomconfiguration.exclude group: 'log4j'
}

dependencies {
    mycustomconfiguration configurations.runtime
}

The configuration that we are referring to in BootRepackage is a normal Gradle configuration. In the above example we created a new configuration named mycustomconfiguration instructing it to derive from a runtime and exclude the log4j group. If the clientBoot task is executed, the repackaged boot jar will have all dependencies from runtime but no log4j jars.

When spring-boot is applied to your Gradle project a default task named bootRepackage is created automatically. The bootRepackage task depends on Gradle assemble task, and when executed, it tries to find all jar artifacts whose qualifier is empty (i.e. tests and sources jars are automatically skipped).

Due to the fact that bootRepackage finds all created jar artifacts, the order of Gradle task execution is important. Most projects only create a single jar file, so usually this is not an issue; however, if you are planning to create a more complex project setup, with custom Jar and BootRepackage tasks, there are few tweaks to consider.

If you are just creating custom jar files from your project you can simply disables default jar and bootRepackage tasks:

jar.enabled = false
bootRepackage.enabled = false

Another option is to instruct the default bootRepackage task to only work with a default jar task.

bootRepackage.withJarTask = jar

If you have a default project setup where the main jar file is created and repackaged, and you still want to create additional custom jars, you can combine your custom repackage tasks together and use dependsOn so that the bootJars task will run after the default bootRepackage task is executed:

task bootJars
bootJars.dependsOn = [clientBoot1,clientBoot2,clientBoot3]
build.dependsOn(bootJars)

All the above tweaks are usually used to avoid situations where an already created boot jar is repackaged again. Repackaging an existing boot jar will not break anything, but you may find that it includes unnecessary dependencies.

To repackage an existing archive so that it becomes a self-contained executable archive use org.springframework.boot.loader.tools.Repackager. The Repackager class takes a single constructor argument that refers to an existing jar or war archive. Use one of the two available repackage() methods to either replace the original file or write to a new destination. Various settings can also be configured on the repackager before it is run.

When repackaging an archive you can include references to dependency files using the org.springframework.boot.loader.tools.Libraries interface. We don’t provide any concrete implementations of Libraries here as they are usually build system specific.

If your archive already includes libraries you can use Libraries.NONE.

If you don’t use Repackager.setMainClass() to specify a main class, the repackager will use ASM to read class files and attempt to find a suitable class with a public static void main(String[] args) method. An exception is thrown if more than one candidate is found.

Here is a typical example repackage:

Repackager repackager = new Repackager(sourceJarFile);
repackager.setBackupSource(false);
repackager.repackage(new Libraries() {
            @Override
            public void doWithLibraries(LibraryCallback callback) throws IOException {
                // Build system specific implementation, callback for each dependency
                // callback.library(nestedFile, LibraryScope.COMPILE);
            }
        });

The Spring Boot auto-configuration tries its best to “do the right thing”, but sometimes things fail and it can be hard to tell why.

There is a really useful AutoConfigurationReport available in any Spring Boot ApplicationContext. You will see it if you enable DEBUG logging output. If you use the spring-boot-actuator there is also an autoconfig endpoint that renders the report in JSON. Use that to debug the application and see what features have been added (and which not) by Spring Boot at runtime.

Many more questions can be answered by looking at the source code and the javadoc. Some rules of thumb:

A SpringApplication has ApplicationListeners and ApplicationContextInitializers that are used to apply customizations to the context or environment. Spring Boot loads a number of such customizations for use internally from META-INF/spring.factories. There is more than one way to register additional ones:

The SpringApplication sends some special ApplicationEvents to the listeners (even some before the context is created), and then registers the listeners for events published by the ApplicationContext as well. See Section 20.3, “Application events and listeners” in the “Spring Boot features” section for a complete list.

You can use the ApplicationBuilder class to create parent/child ApplicationContext hierarchies. See Section 20.2, “Fluent builder API” in the “Spring Boot features” section for more information.

Not all Spring applications have to be web applications (or web services). If you want to execute some code in a main method, but also bootstrap a Spring application to set up the infrastructure to use, then it’s easy with the SpringApplication features of Spring Boot. A SpringApplication changes its ApplicationContext class depending on whether it thinks it needs a web application or not. The first thing you can do to help it is to just leave the servlet API dependencies off the classpath. If you can’t do that (e.g. you are running 2 applications from the same code base) then you can explicitly call SpringApplication.setWebEnvironment(false), or set the applicationContextClass property (through the Java API or with external properties). Application code that you want to run as your business logic can be implemented as a CommandLineRunner and dropped into the context as a @Bean definition.

A SpringApplication has bean properties (mainly setters) so you can use its Java API as you create the application to modify its behavior. Or you can externalize the configuration using properties in spring.main.*. E.g. in application.properties you might have.

spring.main.web_environment=false
spring.main.show_banner=false

and then the Spring Boot banner will not be printed on startup, and the application will not be a web application.

	Note
	The example above also demonstrates how flexible binding allows the use of underscores (_) as well as dashes (-) in property names.

By default properties from different sources are added to the Spring Environment in a defined order (see Chapter 21, Externalized Configuration in the “Spring Boot features” section for the exact order).

A nice way to augment and modify this is to add @PropertySource annotations to your application sources. Classes passed to the SpringApplication static convenience methods, and those added using setSources() are inspected to see if they have @PropertySources, and if they do, those properties are added to the Environment early enough to be used in all phases of the ApplicationContext lifecycle. Properties added in this way have precedence over any added using the default locations, but have lower priority than system properties, environment variables or the command line.

You can also provide System properties (or environment variables) to change the behavior:

No matter what you set in the environment, Spring Boot will always load application.properties as described above. If YAML is used then files with the “.yml” extension are also added to the list by default.

See ConfigFileApplicationListener for more detail.

Some people like to use (for example) --port=9000 instead of --server.port=9000 to set configuration properties on the command line. You can easily enable this by using placeholders in application.properties, e.g.

server.port=${port:8080}

	Tip
	If you have enabled maven filtering for the application.properties you may want to avoid using ${*} for the tokens to filter as it conflicts with those placeholders. You can either use @*@ (i.e. @maven.token@ instead of ${maven.token}) or you can configure the maven-resources-plugin to use other delimiters.

	Note
	In this specific case the port binding will work in a PaaS environment like Heroku and Cloud Foundry, since in those two platforms the PORT environment variable is set automatically and Spring can bind to capitalized synonyms for Environment properties.

YAML is a superset of JSON and as such is a very convenient syntax for storing external properties in a hierarchical format. E.g.

spring:
    application:
        name: cruncher
    datasource:
        driverClassName: com.mysql.jdbc.Driver
        url: jdbc:mysql://localhost/test
server:
    port: 9000

Create a file called application.yml and stick it in the root of your classpath, and also add snakeyaml to your dependencies (Maven coordinates org.yaml:snakeyaml, already included if you use the spring-boot-starter). A YAML file is parsed to a Java Map<String,Object> (like a JSON object), and Spring Boot flattens the map so that it is 1-level deep and has period-separated keys, a lot like people are used to with Properties files in Java.

The example YAML above corresponds to an application.properties file

spring.application.name=cruncher
spring.datasource.driverClassName=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost/test
server.port=9000

See Section 21.5, “Using YAML instead of Properties” in the “Spring Boot features” section for more information about YAML.

The Spring Environment has an API for this, but normally you would set a System profile (spring.profiles.active) or an OS environment variable (SPRING_PROFILES_ACTIVE). E.g. launch your application with a -D argument (remember to put it before the main class or jar archive):

$ java -jar -Dspring.profiles.active=production demo-0.0.1-SNAPSHOT.jar

In Spring Boot you can also set the active profile in application.properties, e.g.

spring.profiles.active=production

A value set this way is replaced by the System property or environment variable setting, but not by the SpringApplicationBuilder.profiles() method. Thus the latter Java API can be used to augment the profiles without changing the defaults.

See Chapter 22, Profiles in the “Spring Boot features” section for more information.

A YAML file is actually a sequence of documents separated by --- lines, and each document is parsed separately to a flattened map.

If a YAML document contains a spring.profiles key, then the profiles value (comma-separated list of profiles) is fed into the Spring Environment.acceptsProfiles() and if any of those profiles is active that document is included in the final merge (otherwise not).

Example:

server:
    port: 9000
---

spring:
    profiles: development
server:
    port: 9001

---

spring:
    profiles: production
server:
    port: 0

In this example the default port is 9000, but if the Spring profile “development” is active then the port is 9001, and if “production” is active then it is 0.

The YAML documents are merged in the order they are encountered (so later values override earlier ones).

To do the same thing with properties files you can use application-${profile}.properties to specify profile-specific values.

Spring Boot binds external properties from application.properties (or .yml) (and other places) into an application at runtime. There is not (and technically cannot be) an exhaustive list of all supported properties in a single location because contributions can come from additional jar files on your classpath.

A running application with the Actuator features has a configprops endpoint that shows all the bound and bindable properties available through @ConfigurationProperties.

The appendix includes an application.properties example with a list of the most common properties supported by Spring Boot. The definitive list comes from searching the source code for @ConfigurationProperties and @Value annotations, as well as the occasional use of RelaxedEnvironment.

Servlet, Filter, ServletContextListener and the other listeners supported by the Servlet spec can be added to your application as @Bean definitions. Be very careful that they don’t cause eager initialization of too many other beans because they have to be installed in the container very early in the application lifecycle (e.g. it’s not a good idea to have them depend on your DataSource or JPA configuration). You can work around restrictions like that by initializing them lazily when first used instead of on initialization.

In the case of Filters and Servlets you can also add mappings and init parameters by adding a FilterRegistrationBean or ServletRegistrationBean instead of or as well as the underlying component.

In a standalone application the main HTTP port defaults to 8080, but can be set with server.port (e.g. in application.properties or as a System property). Thanks to relaxed binding of Environment values you can also use SERVER_PORT (e.g. as an OS environment variable).

To switch off the HTTP endpoints completely, but still create a WebApplicationContext, use server.port=-1 (this is sometimes useful for testing).

For more details look at Section 24.2.3, “Customizing embedded servlet containers” in the “Spring Boot features” section, or the ServerProperties source code.

To scan for a free port (using OS natives to prevent clashes) use server.port=0.

You can access the port the server is running on from log output or from the EmbeddedWebApplicationContext via its EmbeddedServletContainer. The best way to get that and be sure that it has initialized is to add a @Bean of type ApplicationListener<EmbeddedServletContainerInitializedEvent> and pull the container out of the event when it is published.

A really useful thing to do in is to use @IntegrationTest to set server.port=0 and then inject the actual (“local”) port as a @Value. For example:

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = SampleDataJpaApplication.class)
@WebApplication
@IntegrationTest("server.port:0")
public class CityRepositoryIntegrationTests {

    @Autowired
    EmbeddedWebApplicationContext server;

    @Value("${local.server.port}")
    int port;

    // ...

}

Generally you can follow the advice from Section 55.7, “Discover built-in options for external properties” about @ConfigurationProperties (ServerProperties is the main one here), but also look at EmbeddedServletContainerCustomizer and various Tomcat specific *Customizers that you can add in one of those. The Tomcat APIs are quite rich so once you have access to the TomcatEmbeddedServletContainerFactory you can modify it in a number of ways. Or the nuclear option is to add your own TomcatEmbeddedServletContainerFactory.

Use an EmbeddedServletContainerCustomizer and in that add a TomcatConnectorCustomizer that sets up the connector to be secure:

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

// ...

private static class MyCustomizer implements EmbeddedServletContainerCustomizer {

    @Override
    public void customize(ConfigurableEmbeddedServletContainer factory) {
        if(factory instanceof TomcatEmbeddedServletContainerFactory) {
            customizeTomcat((TomcatEmbeddedServletContainerFactory) factory));
        }
    }

    public void customizeTomcat(TomcatEmbeddedServletContainerFactory factory) {
        factory.addConnectorCustomizers(new TomcatConnectorCustomizer() {
            @Override
            public void customize(Connector connector) {
                connector.setPort(serverPort);
                connector.setSecure(true);
                connector.setScheme("https");
                connector.setAttribute("keyAlias", "tomcat");
                connector.setAttribute("keystorePass", "password");
                try {
                    connector.setAttribute("keystoreFile",
                        ResourceUtils.getFile("src/ssl/tomcat.keystore").getAbsolutePath());
                } catch (FileNotFoundException e) {
                    throw new IllegalStateException("Cannot load keystore", e);
                }
                connector.setAttribute("clientAuth", "false");
                connector.setAttribute("sslProtocol", "TLS");
                connector.setAttribute("SSLEnabled", true);
            }
        });
    }

}

Add a org.apache.catalina.connector.Connector to the TomcatEmbeddedServletContainerFactory which can allow multiple connectors eg a HTTP and HTTPS connector:

@Bean
public EmbeddedServletContainerFactory servletContainer() {
    TomcatEmbeddedServletContainerFactory tomcat = new TomcatEmbeddedServletContainerFactory();
    tomcat.addAdditionalTomcatConnectors(createSslConnector());
    return tomcat;
}

private Connector createSslConnector() {
    Connector connector = new Connector("org.apache.coyote.http11.Http11NioProtocol");
    Http11NioProtocol protocol = (Http11NioProtocol) connector.getProtocolHandler();
    try {
        File keystore = new ClassPathResource("keystore").getFile();
        File truststore = new ClassPathResource("keystore").getFile();
        connector.setScheme("https");
        connector.setSecure(true);
        connector.setPort(8443);
        protocol.setSSLEnabled(true);
        protocol.setKeystoreFile(keystore.getAbsolutePath());
        protocol.setKeystorePass("changeit");
        protocol.setTruststoreFile(truststore.getAbsolutePath());
        protocol.setTruststorePass("changeit");
        protocol.setKeyAlias("apitester");
        return connector;
    }
    catch (IOException ex) {
        throw new IllegalStateException("can't access keystore: [" + "keystore"
                + "] or truststore: [" + "keystore" + "]", ex);
    }
}

Spring Boot will automatically configure Tomcat’s RemoteIpValve if it detects some environment settings. This allows you to transparently use the standard x-forwarded-for and x-forwarded-proto headers that most front-end proxy servers add.

You can switch on the valve by adding some entries to application.properties, e.g.

server.tomcat.remote_ip_header=x-forwarded-for
server.tomcat.protocol_header=x-forwarded-proto

Alternatively, you can add the RemoteIpValve yourself by adding a TomcatEmbeddedServletContainerFactory bean.

The Spring Boot starters (spring-boot-starter-web in particular) use Tomcat as an embedded container by default. You need to exclude those dependencies and include the Jetty one instead. Spring Boot provides Tomcat and Jetty dependencies bundled together as separate starters to help make this process as easy as possible.

Example in Maven:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jetty</artifactId>
</dependency>

Example in Gradle:

configurations {
    compile.exclude module: "spring-boot-starter-tomcat"
}

dependencies {
    compile("org.springframework.boot:spring-boot-starter-web:1.0.0.RC3")
    compile("org.springframework.boot:spring-boot-starter-jetty:1.0.0.RC3")
    // ...
}

Generally you can follow the advice from Section 55.7, “Discover built-in options for external properties” about @ConfigurationProperties (ServerProperties is the main one here), but also look at EmbeddedServletContainerCustomizer. The Jetty APIs are quite rich so once you have access to the JettyEmbeddedServletContainerFactory you can modify it in a number of ways. Or the nuclear option is to add your own JettyEmbeddedServletContainerFactory.

Tomcat 8 works with Spring Boot, but the default is to use Tomcat 7 (so we can support Java 1.6 out of the box). You should only need to change the classpath to use Tomcat 8 for it to work. For example, using the starter poms in Maven:

<properties>
    <tomcat.version>8.0.3</tomcat.version>
</properties>
<dependencies>
    ...
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    ...
</dependencies>

change the classpath to use Tomcat 8 for it to work.

Jetty 9 works with Spring Boot, but the default is to use Jetty 8 (so we can support Java 1.6 out of the box). You should only need to change the classpath to use Jetty 9 for it to work.

If you are using the starter poms and parent you can just add the Jetty starter and change the version properties, e.g. for a simple webapp or service:

<properties>
    <java.version>1.7</java.version>
    <jetty.version>9.1.0.v20131115</jetty.version>
    <servlet-api.version>3.1.0</servlet-api.version>
</properties>
<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
        <exclusions>
            <exclusion>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-tomcat</artifactId>
            </exclusion>
        </exclusions>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-jetty</artifactId>
    </dependency>
</dependencies>

Any Spring @RestController in a Spring Boot application should render JSON response by default as long as Jackson2 is on the classpath. For example:

@RestController
public class MyController {

    @RequestMapping("/thing")
    public MyThing thing() {
            return new MyThing();
    }

}

As long as MyThing can be serialized by Jackson2 (e.g. a normal POJO or Groovy object) then http://localhost:8080/thing will serve a JSON representation of it by default. Sometimes in a browser you might see XML responses (but by default only if MyThing was a JAXB object) because browsers tend to send accept headers that prefer XML.

Since JAXB is in the JDK the same example as we used for JSON would work, as long as the MyThing was annotated as @XmlRootElement:

@XmlRootElement
public class MyThing {
    private String name;
    // .. getters and setters
}

To get the server to render XML instead of JSON you might have to send an Accept: text/xml header (or use a browser).

Spring MVC (client and server side) uses HttpMessageConverters to negotiate content conversion in an HTTP exchange. If Jackson is on the classpath you already get a default converter with a vanilla ObjectMapper. Spring Boot has some features to make it easier to customize this behavior.

The smallest change that might work is to just add beans of type com.fasterxml.jackson.databind.Module to your context. They will be registered with the default ObjectMapper and then injected into the default message converter. To replace the default ObjectMapper completely, define a @Bean of that type and mark it as @Primary.

In addition, if your context contains any beans of type ObjectMapper then all of the Module beans will be registered with all of the mappers. So there is a global mechanism for contributing custom modules when you add new features to your application.

Finally, if you provide any @Beans of type MappingJackson2HttpMessageConverter then they will replace the default value in the MVC configuration. Also, a convenience bean is provided of type HttpMessageConverters (always available if you use the default MVC configuration) which has some useful methods to access the default and user-enhanced message converters.

See also the Section 57.4, “Customize the @ResponseBody rendering” section and the WebMvcAutoConfiguration source code for more details.

Spring uses HttpMessageConverters to render @ResponseBody (or responses from @RestController). You can contribute additional converters by simply adding beans of that type in a Spring Boot context. If a bean you add is of a type that would have been included by default anyway (like MappingJackson2HttpMessageConverter for JSON conversions) then it will replace the default value. A convenience bean is provided of type HttpMessageConverters (always available if you use the default MVC configuration) which has some useful methods to access the default and user-enhanced message converters (useful, for example if you want to manually inject them into a custom RestTemplate).

As in normal MVC usage, any WebMvcConfigurerAdapter beans that you provide can also contribute converters by overriding the configureMessageConverters method, but unlike with normal MVC, you can supply only additional converters that you need (because Spring Boot uses the same mechanism to contribute its defaults). Finally, if you opt-out of the Spring Boot default MVC configuration by providing your own @EnableWebMvc configuration, then you can take control completely and do everything manually using getMessageConverters from WebMvcConfigurationSupport.

See the WebMvcAutoConfiguration source code for more details.

Spring Boot wants to serve all content from the root of your application / down. If you would rather map your own servlet to that URL you can do it, but of course you may lose some of the other Boot MVC features. To add your own servlet and map it to the root resource just declare a @Bean of type Servlet and give it the special bean name dispatcherServlet (You can also create a bean of a different type with that name if you want to switch it off and not replace it).

The easiest way to take complete control over MVC configuration is to provide your own @Configuration with the @EnableWebMvc annotation. This will leave all MVC configuration in your hands.

A ViewResolver is a core component of Spring MVC, translating view names in @Controller to actual View implementations. Note that ViewResolvers are mainly used in UI applications, rather than REST-style services (a View is not used to render a @ResponseBody). There are many implementations of ViewResolver to choose from, and Spring on its own is not opinionated about which ones you should use. Spring Boot, on the other hand, installs one or two for you depending on what it finds on the classpath and in the application context. The DispatcherServlet uses all the resolvers it finds in the application context, trying each one in turn until it gets a result, so if you are adding your own you have to be aware of the order and in which position your resolver is added.

WebMvcAutoConfiguration adds the following ViewResolvers to your context:

Checkout WebMvcAutoConfiguration and ThymeleafAutoConfiguration

Spring Boot has no mandatory logging dependence, except for the commons-logging API, of which there are many implementations to choose from. To use Logback you need to include it, and some bindings for commons-logging on the classpath. The simplest way to do that is through the starter poms which all depend on spring-boot-starter-logging. For a web application you only need spring-boot-starter-web since it depends transitively on the logging starter. For example, using Maven:

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

Spring Boot has a LoggingSystem abstraction that attempts to configure logging based on the content of the classpath. If Logback is available it is the first choice. So if you put a logback.xml in the root of your classpath it will be picked up from there. Spring Boot provides a default base configuration that you can include if you just want to set levels, e.g.

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <include resource="org/springframework/boot/logging/logback/base.xml"/>
    <logger name="org.springframework.web" level="DEBUG"/>
</configuration>

If you look at the default logback.xml in the spring-boot jar you will see that it uses some useful System properties which the LoggingSystem takes care of creating for you. These are:

Spring Boot also provides some nice ANSI colour terminal output on a console (but not in a log file) using a custom Logback converter. See the default base.xml configuration for details.

If Groovy is on the classpath you should be able to configure Logback with logback.groovy as well (it will be given preference if present).

Spring Boot supports Log4j for logging configuration, but it has to be on the classpath. If you are using the starter poms for assembling dependencies that means you have to exclude logback and then include log4j instead. If you aren’t using the starter poms then you need to provide commons-logging (at least) in addition to Log4j.

The simplest path to using Log4j is probably through the starter poms, even though it requires some jiggling with excludes, e.g. in Maven:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter</artifactId>
    <exclusions>
            <exclusion>
                    <groupId>${project.groupId}</groupId>
                    <artifactId>spring-boot-starter-logging</artifactId>
            </exclusion>
    </exclusions>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-log4j</artifactId>
</dependency>

	Note
	The use of the log4j starter gathers together the dependencies for common logging requirements (e.g. including having Tomcat use java.util.logging but configure the output using Log4j). See the Actuator Log4j Sample for more detail and to see it in action.

To override the default settings just define a @Bean of your own of type DataSource. See Section 26.1, “Configure a DataSource” in the “Spring Boot features” section and the DataSourceAutoConfiguration class for more details.

Spring Data can create implementations for you of @Repository interfaces of various flavours. Spring Boot will handle all of that for you as long as those @Repositories are included in the same package (or a sub-package) of your @EnableAutoConfiguration class.

For many applications all you will need is to put the right Spring Data dependencies on your classpath (there is a spring-boot-starter-data-jpa for JPA and a spring-boot-starter-data-mongodb for Mongodb), create some repository interfaces to handle your @Entity objects. Examples are in the JPA sample or the Mongodb sample.

Spring Boot tries to guess the location of your @Repository definitions, based on the @EnableAutoConfiguration it finds. To get more control, use the @EnableJpaRepositories annotation (from Spring Data JPA).

Spring Boot tries to guess the location of your @Entity definitions, based on the @EnableAutoConfiguration it finds. To get more control, you can use the @EntityScan annotation, e.g.

@Configuration
@EnableAutoConfiguration
@EntityScan(basePackageClasses=City.class)
public class Application {

    //...

}

Spring Data JPA already provides some vendor-independent configuration options (e.g. for SQL logging) and Spring Boot exposes those, and a few more for hibernate as external configuration properties. The most common options to set are:

spring.jpa.hibernate.ddl-auto: create-drop
spring.jpa.hibernate.naming_strategy: org.hibernate.cfg.ImprovedNamingStrategy
spring.jpa.database: H2
spring.jpa.show-sql: true

(Because of relaxed data binding hyphens or underscores should work equally well as property keys.) The ddl-auto setting is a special case in that it has different defaults depending on whether you are using an embedded database (create-drop) or not (none). In addition all properties in spring.jpa.properties.* are passed through as normal JPA properties (with the prefix stripped) when the local EntityManagerFactory is created.

See HibernateJpaAutoConfiguration and JpaBaseConfiguration for more details.

To take full control of the configuration of the EntityManagerFactory, you need to add a @Bean named "entityManagerFactory". To avoid eager initialization of JPA infrastructure, Spring Boot auto-configuration does not switch on its entity manager based on the presence of a bean of that type. Instead it has to do it by name.

Spring doesn’t require the use of XML to configure the JPA provider, and Spring Boot assumes you want to take advantage of that feature. If you prefer to use persistence.xml then you need to define your own @Bean of type LocalEntityManagerFactoryBean (with id "entityManagerFactory", and set the persistence unit name there.

See JpaBaseConfiguration for the default settings.

JPA has features for DDL generation, and these can be set up to run on startup against the database. This is controlled through two external properties:

You can set spring.jpa.hibernate.ddl-auto explicitly and the standard Hibernate property values are none, validate, update, create-drop. Spring Boot chooses a default value for you based on whether it thinks your database is embedded (default create-drop) or not (default none). An embedded database is detected by looking at the Connection type: hsqldb, h2 and derby are embedded, the rest are not. Be careful when switching from in-memory to a “real” database that you don’t make assumptions about the existence of the tables and data in the new platform. You either have to set ddl-auto explicitly, or use one of the other mechanisms to initialize the database.

In addition, a file named import.sql in the root of the classpath will be executed on startup. This can be useful for demos and for testing if you are careful, but probably not something you want to be on the classpath in production. It is a Hibernate feature (nothing to do with Spring).

Spring JDBC has a DataSource initializer feature. Spring Boot enables it by default and loads SQL from the standard locations schema.sql and data.sql (in the root of the classpath). In addition Spring Boot will load a file schema-${platform}.sql where platform is the value of spring.datasource.platform, e.g. you might choose to set it to the vendor name of the database (hsqldb, h2, oracle, mysql, postgresql etc.). Spring Boot enables the failfast feature of the Spring JDBC initializer by default, so if the scripts cause exceptions the application will fail to start.

To disable the failfast you can set spring.datasource.continueOnError=true. This can be useful once an application has matured and been deployed a few times, since the scripts can act as “poor man’s migrations” — inserts that fail mean that the data is already there, so there would be no need to prevent the application from running, for instance.

If you are using Spring Batch then it comes pre-packaged with SQL initialization scripts for most popular database platforms. Spring Boot will detect your database type, and execute those scripts by default, and in this case will switch the fail fast setting to false (errors are logged but do not prevent the application from starting). This is because the scripts are known to be reliable and generally do not contain bugs, so errors are ignorable, and ignoring them makes the scripts idempotent. You can switch off the initialization explicitly using spring.batch.initializer.enabled=false.

Spring Boot works fine with higher level migration tools Flyway (SQL-based) and Liquibase (XML). In general we prefer Flyway because it is easier on the eyes, and it isn’t very common to need platform independence: usually only one or at most couple of platforms is needed.

Spring Batch auto configuration is enabled by adding @EnableBatchProcessing (from Spring Batch) somewhere in your context.

By default it executes all Jobs in the application context on startup (see JobLauncherCommandLineRunner for details). You can narrow down to a specific job or jobs by specifying spring.batch.job.names (comma separated job name patterns).

If the application context includes a JobRegistry then the jobs in spring.batch.job.names are looked up in the registry instead of being autowired from the context. This is a common pattern with more complex systems where multiple jobs are defined in child contexts and registered centrally.

See BatchAutoConfiguration and @EnableBatchProcessing for more details.

In a standalone application the Actuator HTTP port defaults to the same as the main HTTP port. To make the application listen on a different port set the external property management.port. To listen on a completely different network address (e.g. if you have an internal network for management and an external one for user applications) you can also set management.address to a valid IP address that the server is able to bind to.

For more detail look at the ManagementServerProperties source code and Section 33.3, “Customizing the management server port” in the “Production-ready features” section.

The Actuator installs a “whitelabel” error page that you will see in browser client if you encounter a server error (machine clients consuming JSON and other media types should see a sensible response with the right error code). To switch it off you can set error.whitelabel.enabled=false, but normally in addition or alternatively to that you will want to add your own error page replacing the whitelabel one. If you are using Thymeleaf you can do this by adding an error.html template. In general what you need is a View that resolves with a name of error, and/or a @Controller that handles the /error path. Unless you replaced some of the default configuration you should find a BeanNameViewResolver in your ApplicationContext so a @Bean with id error would be a simple way of doing that. Look at ErrorMvcAutoConfiguration for more options.

If you define a @Configuration with @EnableWebSecurity anywhere in your application it will switch off the default webapp security settings in Spring Boot. To tweak the defaults try setting properties in security.* (see SecurityProperties for details of available settings) and SECURITY section of Common application properties.

If you provide a @Bean of type AuthenticationManager the default one will not be created, so you have the full feature set of Spring Security available (e.g. various authentication options).

Spring Security also provides a convenient AuthenticationManagerBuilder which can be used to build an AuthenticationManager with common options. The recommended way to use this in a webapp is to inject it into a void method in a WebSecurityConfigurerAdapter, e.g.

@Configuration
public class SecurityConfiguration extends WebSecurityConfigurerAdapter {

    @Autowired
    public void configureGlobal(AuthenticationManagerBuilder auth) throws Exception {
            auth.inMemoryAuthentication()
                .withUser("barry").password("password").roles("USER"); // ...  etc.
    }

    // ... other stuff for application security

}

You will get the best results if you put this in a nested class, or a standalone class (i.e. not mixed in with a lot of other @Beans that might be allowed to influence the order of instantiation). The secure web sample is a useful template to follow.

Ensuring that all your main endpoints are only available over HTTPS is an important chore for any application. If you are using Tomcat as a servlet container, then Spring Boot will add Tomcat’s own RemoteIpValve automatically if it detects some environment settings, and you should be able to rely on the HttpServletRequest to report whether it is secure or not (even downstream of a proxy server that handles the real SSL termination). The standard behavior is determined by the presence or absence of certain request headers (x-forwarded-for and x-forwarded-proto), whose names are conventional, so it should work with most front end proxies. You can switch on the valve by adding some entries to application.properties, e.g.

server.tomcat.remote_ip_header=x-forwarded-for
server.tomcat.protocol_header=x-forwarded-proto

(The presence of either of those properties will switch on the valve. Or you can add the RemoteIpValve yourself by adding a TomcatEmbeddedServletContainerFactory bean.)

Spring Security can also be configured to require a secure channel for all (or some requests). To switch that on in a Spring Boot application you just need to set security.require_https to true in application.properties.

There are several options for hot reloading. Running in an IDE (especially with debugging on) is a good way to do development (all modern IDEs allow reloading of static resources and usually also hot-swapping of Java class changes). The Maven and Gradle plugins also support running from the command line with reloading of static files. You can use that with an external css/js compiler process if you are writing that code with higher level tools.

If you are using Thymeleaf, then set spring.thymeleaf.cache to false. See ThymeleafAutoConfiguration for other template customization options.

Modern IDEs (Eclipse, IDEA, etc.) all support hot swapping of bytecode, so if you make a change that doesn’t affect class or method signatures it should reload cleanly with no side effects.

Spring Loaded goes a little further in that it can reload class definitions with changes in the method signatures. With some customization it can force an ApplicationContext to refresh itself (but there is no general mechanism to ensure that would be safe for a running application anyway, so it would only ever be a development time trick probably).

If you use a Maven build that inherits from spring-boot-starter-parent but you want to override a specific third-party dependency you can add appropriate <properties> elements. Browse the spring-dependencies POM for a complete list of properties. For example, to pick a different slf4j version you would add the following:

<properties>
    <slf4j.version>1.7.5<slf4j.version>
</properties>

	Warning
	Each Spring Boot release is designed and tested against a specific set of third-party dependencies. Overriding versions may cause compatibilty issues.