spring-boot/spring-boot-tools/spring-boot-maven-plugin

Spring Boot - Maven Plugin

The Spring Boot Maven Plugin provides Spring Boot support in Maven, allowing you to package executable jar or war archives and run an application in-place. To use it you must be using Maven 3 (or better).

Including the plugin

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>{{project.version}}</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 in the "package" phase of the Maven lifecycle, so

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

will reveal the result. 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, e.g.

$ mvn package spring-boot:repackage

will have the same effect as above.

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>

Packaging executable jar and war files

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 do something like this:

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

Repackage configuration

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

Required Parameters

Name	Type	Description	Default Value
outputDirectory	File	Directory containing the generated archive	${project.build.directory}
finalName	String	Name of the generated archive	${project.build.finalName}

Optional Parameters

Name	Type	Description
classifier	String	Classifier to add to the artifact generated. 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
mainClass	String	The name of the main class. If not specified the first compiled class found that contains a 'main' method will be used
layout	String	The type of archive (which corresponds to how the dependencies are layed 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>{{project.version}}</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).

Running applications

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 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.

Run configuration

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

Required Parameters

Name	Type	Description	Default Value
classesDirectrory	File	Directory containing the classes and resource files that should be packaged into the archive	${project.build.outputDirectory}

Optional Parameters

Name	Type	Description	Default Value
arguments (or -Drun.arguments)	String[]	Arguments that should be passed to the application
addResources (or -Drun.addResources)	boolean	Add maven resources to the classpath directly, this allows live in-place editing or resources. Since resources will be added directly, and via the target/classes folder they will appear twice if ClassLoader.getResources() is called. In practice however most applications call ClassLoader.getResource() which will always return the first resource	true
mainClass	String	The name of the main class. If not specified the first compiled class found that contains a 'main' method will be used
folders	String[]	Folders that should be added to the classpath	${project.build.outputDirectory}

Further Reading

For more information on how Spring Boot Loader archives work, take a look at the spring-boot-loader module. If you prefer using Gradle to build your projects we have a spring-boot-gradle-plugin.