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

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

Spring Boot dependencies use the org.springframework.boot groupId. Typically your Maven POM file will inherit from the spring-boot-starter-parent project and declare dependencies to one or more “Starters”. 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>2.0.0.BUILD-SNAPSHOT</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>

    <!-- Add Spring repositories -->
    <!-- (you don't need this if you are using a .RELEASE version) -->
    <repositories>
        <repository>
            <id>spring-snapshots</id>
            <url>http://repo.spring.io/snapshot</url>
            <snapshots><enabled>true</enabled></snapshots>
        </repository>
        <repository>
            <id>spring-milestones</id>
            <url>http://repo.spring.io/milestone</url>
        </repository>
    </repositories>
    <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>
</project>

	Tip
	The spring-boot-starter-parent is a great way to use Spring Boot, but it might not be suitable all of the time. Sometimes you may need to inherit from a different parent POM, or you might just not like our default settings. See Section 13.2.2, “Using Spring Boot without the parent POM” for an alternative solution that uses an import scope.

Spring Boot is compatible with Gradle 1.12 or 2.x. 2.14.1 is recommended. Gradle 3 is not supported. If you don’t already have Gradle installed you can follow the instructions at www.gradle.org/.

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

Here is a typical build.gradle file:

buildscript {
    repositories {
        jcenter()
        maven { url "http://repo.spring.io/snapshot" }
        maven { url "http://repo.spring.io/milestone" }
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:2.0.0.BUILD-SNAPSHOT")
    }
}

apply plugin: 'java'
apply plugin: 'org.springframework.boot'

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

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

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

You can download the Spring CLI distribution from the Spring software repository:

Cutting edge snapshot distributions are also available.

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

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

$ sdk install springboot
$ spring --version
Spring Boot v2.0.0.BUILD-SNAPSHOT

If you are developing features for the CLI and want easy access to the version you just built, follow these extra instructions.

$ sdk install springboot dev /path/to/spring-boot/spring-boot-cli/target/spring-boot-cli-2.0.0.BUILD-SNAPSHOT-bin/spring-2.0.0.BUILD-SNAPSHOT/
$ sdk default springboot dev
$ spring --version
Spring CLI v2.0.0.BUILD-SNAPSHOT

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

You can see it by doing this:

$ sdk ls springboot

================================================================================
Available Springboot Versions
================================================================================
> + dev
* 2.0.0.BUILD-SNAPSHOT

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

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.

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

$ sudo port install spring-boot-cli

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 SDKMAN!

$ . ~/.sdkman/candidates/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 or MacPorts, the command-line completion scripts are automatically registered with your shell.

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

@RestController
class ThisWillActuallyRun {

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

}

Then simply run it from a shell:

$ spring run app.groovy

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

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

Hello World!

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.

The second class-level annotation is @EnableAutoConfiguration. This annotation tells Spring Boot to “guess” how you will want to configure Spring, based on the jar dependencies that you have added. Since spring-boot-starter-web added Tomcat and Spring MVC, the auto-configuration will assume that you are developing a web application and setup Spring accordingly.

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

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>2.0.0.BUILD-SNAPSHOT</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.

With that setup, you can also override individual dependencies by overriding a property in your own project. For instance, to upgrade to another Spring Data release train you’d add the following to your pom.xml.

<properties>
    <spring-data-releasetrain.version>Fowler-SR2</spring-data-releasetrain.version>
</properties>

	Tip
	Check the spring-boot-dependencies pom for a list of supported properties.

Not everyone likes inheriting from the spring-boot-starter-parent POM. You may have your own corporate standard parent that you need to use, or you may just prefer to explicitly declare all your Maven configuration.

If you don’t want to use the spring-boot-starter-parent, you can still keep the benefit of the dependency management (but not the plugin management) by using a scope=import dependency:

<dependencyManagement>
     <dependencies>
        <dependency>
            <!-- Import dependency management from Spring Boot -->
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-dependencies</artifactId>
            <version>2.0.0.BUILD-SNAPSHOT</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

That setup does not allow you to override individual dependencies using a property as explained above. To achieve the same result, you’d need to add an entry in the dependencyManagement of your project before the spring-boot-dependencies entry. For instance, to upgrade to another Spring Data release train you’d add the following to your pom.xml.

<dependencyManagement>
    <dependencies>
        <!-- Override Spring Data release train provided by Spring Boot -->
        <dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-releasetrain</artifactId>
            <version>Fowler-SR2</version>
            <scope>import</scope>
            <type>pom</type>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-dependencies</artifactId>
            <version>2.0.0.BUILD-SNAPSHOT</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

	Note
	In the example above, we specify a BOM but any dependency type can be overridden that way.

The spring-boot-starter-parent chooses fairly conservative Java compatibility. If you want to follow our recommendation and use a later Java version you can add a java.version property:

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

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

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

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

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

spring.devtools.restart.exclude=static/**,public/**

	Tip
	if you want to keep those defaults and add additional exclusions, use the spring.devtools.restart.additional-exclude property instead.

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

If you don’t want to use the restart feature you can disable it using the spring.devtools.restart.enabled property. In most cases you can set this in your application.properties (this will still initialize the restart classloader but it won’t watch for file changes).

If you need to completely disable restart support, for example, because it doesn’t work with a specific library, you need to set a System property before calling SpringApplication.run(…​). For example:

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

If you work with an IDE that continuously compiles changed files, you might prefer to trigger restarts only at specific times. To do this you can use a “trigger file”, which is a special file that must be modified when you want to actually trigger a restart check. Changing the file only triggers the check and the restart will only occur if Devtools has detected it has to do something. The trigger file could be updated manually, or via an IDE plugin.

To use a trigger file use the spring.devtools.restart.trigger-file property.

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

As described in the Restart vs Reload section above, restart functionality is implemented by using two classloaders. For most applications this approach works well, however, sometimes it can cause classloading issues.

By default, any open project in your IDE will be loaded using the “restart” classloader, and any regular .jar file will be loaded using the “base” classloader. If you work on a multi-module project, and not each module is imported into your IDE, you may need to customize things. To do this you can create a META-INF/spring-devtools.properties file.

The spring-devtools.properties file can contain restart.exclude. and restart.include. prefixed properties. The include elements are items that should be pulled up into the “restart” classloader, and the exclude elements are items that should be pushed down into the “base” classloader. The value of the property is a regex pattern that will be applied to the classpath.

For example:

restart.exclude.companycommonlibs=/mycorp-common-[\\w-]+\.jar
restart.include.projectcommon=/mycorp-myproj-[\\w-]+\.jar

	Note
	All property keys must be unique. As long as a property starts with restart.include. or restart.exclude. it will be considered.

	Tip
	All META-INF/spring-devtools.properties from the classpath will be loaded. You can package files inside your project, or in the libraries that the project consumes.

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

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

The remote client application is designed to be run from within you IDE. You need to run org.springframework.boot.devtools.RemoteSpringApplication using the same classpath as the remote project that you’re connecting to. The non-option argument passed to the application should be the remote URL that you are connecting to.

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

A running remote client will look like this:

  .   ____          _                                              __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _          ___               _      \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` |        | _ \___ _ __  ___| |_ ___ \ \ \ \
 \\/  ___)| |_)| | | | | || (_| []::::::[]   / -_) '  \/ _ \  _/ -_) ) ) ) )
  '  |____| .__|_| |_|_| |_\__, |        |_|_\___|_|_|_\___/\__\___|/ / / /
 =========|_|==============|___/===================================/_/_/_/
 :: Spring Boot Remote :: 2.0.0.BUILD-SNAPSHOT

2015-06-10 18:25:06.632  INFO 14938 --- [           main] o.s.b.devtools.RemoteSpringApplication   : Starting RemoteSpringApplication on pwmbp with PID 14938 (/Users/pwebb/projects/spring-boot/code/spring-boot-devtools/target/classes started by pwebb in /Users/pwebb/projects/spring-boot/code/spring-boot-samples/spring-boot-sample-devtools)
2015-06-10 18:25:06.671  INFO 14938 --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@2a17b7b6: startup date [Wed Jun 10 18:25:06 PDT 2015]; root of context hierarchy
2015-06-10 18:25:07.043  WARN 14938 --- [           main] o.s.b.d.r.c.RemoteClientConfiguration    : The connection to http://localhost:8080 is insecure. You should use a URL starting with 'https://'.
2015-06-10 18:25:07.074  INFO 14938 --- [           main] o.s.b.d.a.OptionalLiveReloadServer       : LiveReload server is running on port 35729
2015-06-10 18:25:07.130  INFO 14938 --- [           main] o.s.b.devtools.RemoteSpringApplication   : Started RemoteSpringApplication in 0.74 seconds (JVM running for 1.105)

	Note
	Because the remote client is using the same classpath as the real application it can directly read application properties. This is how the spring.devtools.remote.secret property is read and passed to the server for authentication.

	Tip
	It’s always advisable to use https:// as the connection protocol so that traffic is encrypted and passwords cannot be intercepted.

	Tip
	If you need to use a proxy to access the remote application, configure the spring.devtools.remote.proxy.host and spring.devtools.remote.proxy.port properties.

The remote client will monitor your application classpath for changes in the same way as the local restart. Any updated resource will be pushed to the remote application and (if required) trigger a restart. This can be quite helpful if you are iterating on a feature that uses a cloud service that you don’t have locally. Generally remote updates and restarts are much quicker than a full rebuild and deploy cycle.

	Note
	Files are only monitored when the remote client is running. If you change a file before starting the remote client, it won’t be pushed to the remote server.

Java remote debugging is useful when diagnosing issues on a remote application. Unfortunately, it’s not always possible to enable remote debugging when your application is deployed outside of your data center. Remote debugging can also be tricky to setup if you are using a container based technology such as Docker.

To help work around these limitations, devtools supports tunneling of remote debug traffic over HTTP. The remote client provides a local server on port 8000 that you can attach a remote debugger to. Once a connection is established, debug traffic is sent over HTTP to the remote application. You can use the spring.devtools.remote.debug.local-port property if you want to use a different port.

You’ll need to ensure that your remote application is started with remote debugging enabled. Often this can be achieved by configuring JAVA_OPTS. For example, with Cloud Foundry you can add the following to your manifest.yml:

---
  env:
    JAVA_OPTS: "-Xdebug -Xrunjdwp:server=y,transport=dt_socket,suspend=n"

	Tip
	Notice that you don’t need to pass an address=NNNN option to -Xrunjdwp. If omitted Java will simply pick a random free port.

	Note
	Debugging a remote service over the Internet can be slow and you might need to increase timeouts in your IDE. For example, in Eclipse you can select Java → Debug from Preferences…​ and change the Debugger timeout (ms) to a more suitable value (60000 works well in most situations).

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

For example, the following YAML document:

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

Would be transformed into these properties:

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

YAML lists are represented as property keys with [index] dereferencers, for example this YAML:

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

Would be transformed into these properties:

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

To bind to properties like that using the Spring DataBinder utilities (which is what @ConfigurationProperties does) you need to have a property in the target bean of type java.util.List (or Set) and you either need to provide a setter, or initialize it with a mutable value, e.g. this will bind to the properties above

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

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

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

The YamlPropertySourceLoader class can be used to expose YAML as a PropertySource in the Spring Environment. This allows you to use the familiar @Value annotation with placeholders syntax to access YAML properties.

You can specify multiple profile-specific YAML documents in a single file by using a spring.profiles key to indicate when the document applies. For example:

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

In the example above, the server.address property will be 127.0.0.1 if the development profile is active. If the development and production profiles are not enabled, then the value for the property will be 192.168.1.100.

The default profiles are activated if none are explicitly active when the application context starts. So in this YAML we set a value for security.user.password that is only available in the "default" profile:

server:
  port: 8000
---
spring:
  profiles: default
security:
  user:
    password: weak

whereas in this example, the password is always set because it isn’t attached to any profile, and it would have to be explicitly reset in all other profiles as necessary:

server:
  port: 8000
security:
  user:
    password: weak

Spring profiles designated using the "spring.profiles" element may optionally be negated using the ! character. If both negated and non-negated profiles are specified for a single document, at least one non-negated profile must match and no negated profiles may match.

YAML files can’t be loaded via the @PropertySource annotation. So in the case that you need to load values that way, you need to use a properties file.

As we have seen above, any YAML content is ultimately transformed to properties. That process may be counter intuitive when overriding “list” properties via a profile.

For example, assume a MyPojo object with name and description attributes that are null by default. Let’s expose a list of MyPojo from FooProperties:

@ConfigurationProperties("foo")
public class FooProperties {

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

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

}

Consider the following configuration:

foo:
  list:
    - name: my name
      description: my description
---
spring:
  profiles: dev
foo:
  list:
    - name: my another name

If the dev profile isn’t active, FooProperties.list will contain one MyPojo entry as defined above. If the dev profile is enabled however, the list will still only contain one entry (with name “my another name” and description null). This configuration will not add a second MyPojo instance to the list, and it won’t merge the items.

When a collection is specified in multiple profiles, the one with highest priority is used (and only that one):

foo:
  list:
    - name: my name
      description: my description
    - name: another name
      description: another description
---
spring:
  profiles: dev
foo:
  list:
     - name: my another name

In the example above, considering that the dev profile is active, FooProperties.list will contain one MyPojo entry (with name “my another name” and description null).

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

To configure a bean from the Environment properties, add @ConfigurationProperties to its bean registration:

@ConfigurationProperties(prefix = "foo")
@Bean
public FooComponent fooComponent() {
    ...
}

Any property defined with the foo prefix will be mapped onto that FooComponent bean in a similar manner as the ConnectionProperties example above.

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

For example, given the following @ConfigurationProperties class:

@ConfigurationProperties(prefix="person")
public class OwnerProperties {

    private String firstName;

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

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

}

The following properties names can all be used:

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

Note

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

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:

@ConfigurationProperties(prefix="connection")
public class ConnectionProperties {

    @NotNull
    private InetAddress remoteAddress;

    // ... getters and setters

}

In order to validate values of nested properties, you must annotate the associated field as @Valid to trigger its validation. For example, building upon the above ConnectionProperties example:

@ConfigurationProperties(prefix="connection")
public class ConnectionProperties {

    @NotNull
    @Valid
    private RemoteAddress remoteAddress;

    // ... getters and setters

    public static class RemoteAddress {

        @NotEmpty
        public String hostname;

        // ... getters and setters

    }

}

You can also add a custom Spring Validator by creating a bean definition called configurationPropertiesValidator. The @Bean method should be declared static. The configuration properties validator is created very early in the application’s lifecycle and declaring the @Bean method as static allows the bean to be created without having to instantiate the @Configuration class. This avoids any problems that may be caused by early instantiation. There is a property validation sample so you can see how to set things up.

	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.

@Value is a core container feature and it does not provide the same features as type-safe Configuration Properties. The table below summarizes the features that are supported by @ConfigurationProperties and @Value:

If you define a set of configuration keys for your own components, we recommend you to group them in a POJO annotated with @ConfigurationProperties. Please also be aware that since @Value does not support relaxed binding, it isn’t a great candidate if you need to provide the value using environment variables.

Finally, while you can write a SpEL expression in @Value, such expressions are not processed from Application property files.

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

Color coding is configured using the %clr conversion word. In its simplest form the converter will color the output according to the log level, for example:

%clr(%5p)

The mapping of log level to a color is as follows:

Alternatively, you can specify the color or style that should be used by providing it as an option to the conversion. For example, to make the text yellow:

%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){yellow}

The following colors and styles are supported:

The <springProfile> tag allows you to optionally include or exclude sections of configuration based on the active Spring profiles. Profile sections are supported anywhere within the <configuration> element. Use the name attribute to specify which profile accepts the configuration. Multiple profiles can be specified using a comma-separated list.

<springProfile name="staging">
    <!-- configuration to be enabled when the "staging" profile is active -->
</springProfile>

<springProfile name="dev, staging">
    <!-- configuration to be enabled when the "dev" or "staging" profiles are active -->
</springProfile>

<springProfile name="!production">
    <!-- configuration to be enabled when the "production" profile is not active -->
</springProfile>

The <springProperty> tag allows you to surface properties from the Spring Environment for use within Logback. This can be useful if you want to access values from your application.properties file in your logback configuration. The tag works in a similar way to Logback’s standard <property> tag, but rather than specifying a direct value you specify the source of the property (from the Environment). You can use the scope attribute if you need to store the property somewhere other than in local scope. If you need a fallback value in case the property is not set in the Environment, you can use the defaultValue attribute.

<springProperty scope="context" name="fluentHost" source="myapp.fluentd.host"
        defaultValue="localhost"/>
<appender name="FLUENT" class="ch.qos.logback.more.appenders.DataFluentAppender">
    <remoteHost>${fluentHost}</remoteHost>
    ...
</appender>

	Tip
	The RelaxedPropertyResolver is used to access Environment properties. If specify the source in dashed notation (my-property-name) all the relaxed variations will be tried (myPropertyName, MY_PROPERTY_NAME etc).

Spring Boot provides auto-configuration for Spring MVC that works well with most applications.

The auto-configuration adds the following features on top of Spring’s defaults:

If you want to keep Spring Boot MVC features, and you just want to add additional MVC configuration (interceptors, formatters, view controllers etc.) you can add your own @Configuration class of type WebMvcConfigurerAdapter, but without @EnableWebMvc. If you wish to provide custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter or ExceptionHandlerExceptionResolver you can declare a WebMvcRegistrationsAdapter instance providing such components.

If you want to take complete control of Spring MVC, you can add your own @Configuration annotated with @EnableWebMvc.

Spring MVC uses the HttpMessageConverter interface to convert HTTP requests and responses. Sensible defaults are included out of the box, for example Objects can be automatically converted to JSON (using the Jackson library) or XML (using the Jackson XML extension if available, else using JAXB). Strings are encoded using UTF-8 by default.

If you need to add or customize converters you can use Spring Boot’s HttpMessageConverters class:

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);
    }

}

Any HttpMessageConverter bean that is present in the context will be added to the list of converters. You can also override default converters that way.

If you’re using Jackson to serialize and deserialize JSON data, you might want to write your own JsonSerializer and JsonDeserializer classes. Custom serializers are usually registered with Jackson via a Module, but Spring Boot provides an alternative @JsonComponent annotation which makes it easier to directly register Spring Beans.

You can use @JsonComponent directly on JsonSerializer or JsonDeserializer implementations. You can also use it on classes that contains serializers/deserializers as inner-classes. For example:

import java.io.*;
import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.databind.*;
import org.springframework.boot.jackson.*;

@JsonComponent
public class Example {

    public static class Serializer extends JsonSerializer<SomeObject> {
        // ...
    }

    public static class Deserializer extends JsonDeserializer<SomeObject> {
        // ...
    }

}

All @JsonComponent beans in the ApplicationContext will be automatically registered with Jackson, and since @JsonComponent is meta-annotated with @Component, the usual component-scanning rules apply.

Spring Boot also provides JsonObjectSerializer and JsonObjectDeserializer base classes which provide useful alternatives to the standard Jackson versions when serializing Objects. See the Javadoc for details.

Spring MVC has a strategy for generating error codes for rendering error messages from binding errors: MessageCodesResolver. Spring Boot will create one for you if you set the spring.mvc.message-codes-resolver.format property PREFIX_ERROR_CODE or POSTFIX_ERROR_CODE (see the enumeration in DefaultMessageCodesResolver.Format).

By default Spring Boot will serve static content from a directory called /static (or /public or /resources or /META-INF/resources) in the classpath or from the root of the ServletContext. It uses the ResourceHttpRequestHandler from Spring MVC so 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.

You can customize the static resource locations using spring.resources.staticLocations (replacing the default values with a list of directory locations). If you do this the default welcome page detection will switch to your custom locations, so if there is an index.html in any of your locations on startup, it will be the home page of the application.

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 directory if your application will be packaged as a jar. Although this directory 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.

Spring Boot also supports advanced resource handling features provided by Spring MVC, allowing use cases such as cache busting static resources or using version agnostic URLs for Webjars.

To use version agnostic URLs for Webjars, simply add the webjars-locator dependency. Then declare your Webjar, taking jQuery for example, as "/webjars/jquery/dist/jquery.min.js" which results in "/webjars/jquery/x.y.z/dist/jquery.min.js" where x.y.z is the Webjar version.

	Note
	If you are using JBoss, you’ll need to declare the webjars-locator-jboss-vfs dependency instead of the webjars-locator; otherwise all Webjars resolve as a 404.

To use cache bursting, the following configuration will configure a cache busting solution for all static resources, effectively adding a content hash in URLs, such as <link href="/css/spring-2a2d595e6ed9a0b24f027f2b63b134d6.css"/>:

spring.resources.chain.strategy.content.enabled=true
spring.resources.chain.strategy.content.paths=/**

	Note
	Links to resources are rewritten at runtime in template, thanks to a <<<<<<< HEAD ResourceUrlEncodingFilter, auto-configured for Thymeleaf and FreeMarker. You should manually declare this filter when using JSPs. Other template engines aren’t automatically supported right now, but can be with custom template macros/helpers and the use of the

ResourceUrlEncodingFilter, auto-configured for Thymeleaf and FreeMarker. You should manually declare this filter when using JSPs. Other template engines aren’t automatically supported right now, but can be with custom template macros/helpers and the use of the >>>>>>> 1.5.x ResourceUrlProvider.

When loading resources dynamically with, for example, a JavaScript module loader, renaming files is not an option. That’s why other strategies are also supported and can be combined. A "fixed" strategy will add a static version string in the URL, without changing the file name:

spring.resources.chain.strategy.content.enabled=true
spring.resources.chain.strategy.content.paths=/**
spring.resources.chain.strategy.fixed.enabled=true
spring.resources.chain.strategy.fixed.paths=/js/lib/
spring.resources.chain.strategy.fixed.version=v12

With this configuration, JavaScript modules located under "/js/lib/" will use a fixed versioning strategy "/v12/js/lib/mymodule.js" while other resources will still use the content one <link href="/css/spring-2a2d595e6ed9a0b24f027f2b63b134d6.css"/>.

See ResourceProperties for more of the supported options.

	Tip
	This feature has been thoroughly described in a dedicated blog post and in Spring Framework’s reference documentation.

==== ConfigurableWebBindingInitializer Spring MVC uses a WebBindingInitializer to initialize a WebDataBinder for a particular request. If you create your own ConfigurableWebBindingInitializer @Bean, Spring Boot will automatically configure Spring MVC to use it.

==== Template engines As well as REST web services, you can also use Spring MVC to serve dynamic HTML content. <<<<<<< HEAD Spring MVC supports a variety of templating technologies including FreeMarker

Spring MVC supports a variety of templating technologies including Thymeleaf, FreeMarker >>>>>>> 1.5.x and JSPs. Many other templating engines also ship their own Spring MVC integrations.

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

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

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

Tip

IntelliJ IDEA orders the classpath differently depending on how you run your application. Running your application in the IDE via its main method will result in a different ordering to when you run your application using Maven or Gradle or from its packaged jar. This can cause Spring Boot to fail to find the templates on the classpath. If you’re affected by this problem you can reorder the classpath in the IDE to place the module’s classes and resources first. Alternatively, you can configure the template prefix to search every templates directory on the classpath: classpath*:/templates/.

Spring Boot provides an /error mapping by default that handles all errors in a sensible way, and it is registered as a ‘global’ error page in the servlet container. For machine clients it will produce a JSON response with details of the error, the HTTP status and the exception message. For browser clients there is a ‘whitelabel’ error view that renders the same data in HTML format (to customize it just add a View that resolves to ‘error’). To replace the default behaviour completely you can implement ErrorController and register a bean definition of that type, or simply add a bean of type ErrorAttributes to use the existing mechanism but replace the contents.

Tip

The BasicErrorController can be used as a base class for a custom ErrorController. This is particularly useful if you want to add a handler for a new content type (the default is to handle text/html specifically and provide a fallback for everything else). To do that just extend BasicErrorController and add a public method with a @RequestMapping that has a produces attribute, and create a bean of your new type.

You can also define a @ControllerAdvice to customize the JSON document to return for a particular controller and/or exception type.

@ControllerAdvice(basePackageClasses = FooController.class)
public class FooControllerAdvice extends ResponseEntityExceptionHandler {

    @ExceptionHandler(YourException.class)
    @ResponseBody
    ResponseEntity<?> handleControllerException(HttpServletRequest request, Throwable ex) {
        HttpStatus status = getStatus(request);
        return new ResponseEntity<>(new CustomErrorType(status.value(), ex.getMessage()), status);
    }

    private HttpStatus getStatus(HttpServletRequest request) {
        Integer statusCode = (Integer) request.getAttribute("javax.servlet.error.status_code");
        if (statusCode == null) {
            return HttpStatus.INTERNAL_SERVER_ERROR;
        }
        return HttpStatus.valueOf(statusCode);
    }

}

In the example above, if YourException is thrown by a controller defined in the same package as FooController, a json representation of the CustomerErrorType POJO will be used instead of the ErrorAttributes representation.

src/
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- public/
             +- error/
             |   +- 404.html
             +- <other public assets>

src/
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- templates/
             +- error/
             |   +- 5xx.ftl
             +- <other templates>

public class MyErrorViewResolver implements ErrorViewResolver {

    @Override
    public ModelAndView resolveErrorView(HttpServletRequest request,
            HttpStatus status, Map<String, Object> model) {
        // Use the request or status to optionally return a ModelAndView
        return ...
    }

}

@Bean
public ErrorPageRegistrar errorPageRegistrar(){
    return new MyErrorPageRegistrar();
}

// ...

private static class MyErrorPageRegistrar implements ErrorPageRegistrar {

    @Override
    public void registerErrorPages(ErrorPageRegistry registry) {
        registry.addErrorPages(new ErrorPage(HttpStatus.BAD_REQUEST, "/400"));
    }

}

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

If you’re developing a RESTful API that makes use of hypermedia, Spring Boot provides auto-configuration for Spring HATEOAS that works well with most applications. The auto-configuration replaces the need to use @EnableHypermediaSupport and registers a number of beans to ease building hypermedia-based applications including a LinkDiscoverers (for client side support) and an ObjectMapper configured to correctly marshal responses into the desired representation. The ObjectMapper will be customized based on the spring.jackson.* properties or a Jackson2ObjectMapperBuilder bean if one exists.

You can take control of Spring HATEOAS’s configuration by using @EnableHypermediaSupport. Note that this will disable the ObjectMapper customization described above.

Cross-origin resource sharing (CORS) is a W3C specification implemented by most browsers that allows you to specify in a flexible way what kind of cross domain requests are authorized, instead of using some less secure and less powerful approaches like IFRAME or JSONP.

As of version 4.2, Spring MVC supports CORS out of the box. Using controller method CORS configuration with @CrossOrigin annotations in your Spring Boot application does not require any specific configuration. Global CORS configuration can be defined by registering a WebMvcConfigurer bean with a customized addCorsMappings(CorsRegistry) method:

@Configuration
public class MyConfiguration {

    @Bean
    public WebMvcConfigurer corsConfigurer() {
        return new WebMvcConfigurerAdapter() {
            @Override
            public void addCorsMappings(CorsRegistry registry) {
                registry.addMapping("/api/**");
            }
        };
    }
}

When using an embedded servlet container you can register Servlets, Filters and all the listeners from the Servlet spec (e.g. HttpSessionListener) either by using Spring beans or by scanning for Servlet components.

Embedded servlet containers will not directly execute the Servlet 3.0+ javax.servlet.ServletContainerInitializer interface, or Spring’s org.springframework.web.WebApplicationInitializer interface. This is an intentional design decision intended to reduce the risk that 3rd party libraries designed to run inside a war will break Spring Boot applications.

If you need to perform servlet context initialization in a Spring Boot application, you should register a bean that implements the org.springframework.boot.context.embedded.ServletContextInitializer interface. The single onStartup method provides access to the ServletContext, and can easily be used as an adapter to an existing WebApplicationInitializer if necessary.

Scanning for Servlets, Filters, and listeners

When using an embedded container, automatic registration of @WebServlet, @WebFilter, and @WebListener annotated classes can be enabled using @ServletComponentScan.

	Tip
	@ServletComponentScan will have no effect in a standalone container, where the container’s built-in discovery mechanisms will be used instead.

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

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

Common servlet container settings can be configured using Spring Environment properties. Usually you would define the properties in your application.properties file.

Common server settings include:

Spring Boot tries as much as possible to expose common settings but this is not always possible. For those cases, dedicated namespaces offer server-specific customizations (see server.tomcat and server.undertow). For instance, access logs can be configured with specific features of the embedded servlet container.

	Tip
	See the ServerProperties class for a complete list.

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.NOT_FOUND, "/notfound.html"));
    return factory;
}

When running a Spring Boot application that uses an embedded servlet container (and is packaged as an executable archive), there are some limitations in the JSP support.

There is a JSP sample so you can see how to set things up.

To create an Authorization Server and grant access tokens you need to use @EnableAuthorizationServer and provide security.oauth2.client.client-id and security.oauth2.client.client-secret] properties. The client will be registered for you in an in-memory repository.

Having done that you will be able to use the client credentials to create an access token, for example:

$ curl client:secret@localhost:8080/oauth/token -d grant_type=password -d username=user -d password=pwd

The basic auth credentials for the /token endpoint are the client-id and client-secret. The user credentials are the normal Spring Security user details (which default in Spring Boot to “user” and a random password).

To switch off the auto-configuration and configure the Authorization Server features yourself just add a @Bean of type AuthorizationServerConfigurer.

To use the access token you need a Resource Server (which can be the same as the Authorization Server). Creating a Resource Server is easy, just add @EnableResourceServer and provide some configuration to allow the server to decode access tokens. If your application is also an Authorization Server it already knows how to decode tokens, so there is nothing else to do. If your app is a standalone service then you need to give it some more configuration, one of the following options:

If you specify both the user-info-uri and the token-info-uri then you can set a flag to say that one is preferred over the other (prefer-token-info=true is the default).

Alternatively (instead of user-info-uri or token-info-uri) if the tokens are JWTs you can configure a security.oauth2.resource.jwt.key-value to decode them locally (where the key is a verification key). The verification key value is either a symmetric secret or PEM-encoded RSA public key. If you don’t have the key and it’s public you can provide a URI where it can be downloaded (as a JSON object with a “value” field) with security.oauth2.resource.jwt.key-uri. E.g. on PWS:

$ curl https://uaa.run.pivotal.io/token_key
{"alg":"SHA256withRSA","value":"-----BEGIN PUBLIC KEY-----\nMIIBI...\n-----END PUBLIC KEY-----\n"}

	Warning
	If you use the security.oauth2.resource.jwt.key-uri the authorization server needs to be running when your application starts up. It will log a warning if it can’t find the key, and tell you what to do to fix it.

To make your web-app into an OAuth2 client you can simply add @EnableOAuth2Client and Spring Boot will create a OAuth2ClientContext and OAuth2ProtectedResourceDetails that are necessary to create an OAuth2RestOperations. Spring Boot does not automatically create such bean but you can easily create your own:

@Bean
public OAuth2RestTemplate oauth2RestTemplate(OAuth2ClientContext oauth2ClientContext,
        OAuth2ProtectedResourceDetails details) {
    return new OAuth2RestTemplate(details, oauth2ClientContext);
}

	Note
	You may want to add a qualifier and review your configuration as more than one RestTemplate may be defined in your application.

This configuration uses security.oauth2.client.* as credentials (the same as you might be using in the Authorization Server), but in addition it will need to know the authorization and token URIs in the Authorization Server. For example:

application.yml. 

security:
    oauth2:
        client:
            clientId: bd1c0a783ccdd1c9b9e4
            clientSecret: 1a9030fbca47a5b2c28e92f19050bb77824b5ad1
            accessTokenUri: https://github.com/login/oauth/access_token
            userAuthorizationUri: https://github.com/login/oauth/authorize
            clientAuthenticationScheme: form

An application with this configuration will redirect to Github for authorization when you attempt to use the OAuth2RestTemplate. If you are already signed into Github you won’t even notice that it has authenticated. These specific credentials will only work if your application is running on port 8080 (register your own client app in Github or other provider for more flexibility).

To limit the scope that the client asks for when it obtains an access token you can set security.oauth2.client.scope (comma separated or an array in YAML). By default the scope is empty and it is up to Authorization Server to decide what the defaults should be, usually depending on the settings in the client registration that it holds.

	Note
	There is also a setting for security.oauth2.client.client-authentication-scheme which defaults to “header” (but you might need to set it to “form” if, like Github for instance, your OAuth2 provider doesn’t like header authentication). In fact, the security.oauth2.client.* properties are bound to an instance of AuthorizationCodeResourceDetails so all its properties can be specified.

Tip

In a non-web application you can still create an OAuth2RestOperations and it is still wired into the security.oauth2.client.* configuration. In this case it is a “client credentials token grant” you will be asking for if you use it (and there is no need to use @EnableOAuth2Client or @EnableOAuth2Sso). To prevent that infrastructure to be defined, just remove the security.oauth2.client.client-id from your configuration (or make it the empty string).

An OAuth2 Client can be used to fetch user details from the provider (if such features are available) and then convert them into an Authentication token for Spring Security. The Resource Server above support this via the user-info-uri property This is the basis for a Single Sign On (SSO) protocol based on OAuth2, and Spring Boot makes it easy to participate by providing an annotation @EnableOAuth2Sso. The Github client above can protect all its resources and authenticate using the Github /user/ endpoint, by adding that annotation and declaring where to find the endpoint (in addition to the security.oauth2.client.* configuration already listed above):

application.yml. 

security:
    oauth2:
...
    resource:
        userInfoUri: https://api.github.com/user
        preferTokenInfo: false

Since all paths are secure by default, there is no “home” page that you can show to unauthenticated users and invite them to login (by visiting the /login path, or the path specified by security.oauth2.sso.login-path).

To customize the access rules or paths to protect, so you can add a “home” page for instance, @EnableOAuth2Sso can be added to a WebSecurityConfigurerAdapter and the annotation will cause it to be decorated and enhanced with the necessary pieces to get the /login path working. For example, here we simply allow unauthenticated access to the home page at "/" and keep the default for everything else:

@Configuration
public class WebSecurityConfiguration extends WebSecurityConfigurerAdapter {

    @Override
    public void init(WebSecurity web) {
        web.ignore("/");
    }

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http.antMatcher("/**").authorizeRequests().anyRequest().authenticated();
    }

}