Repackaging an application

In order to repackage your application, you simply need to add a reference to the plugin in your pom.xml:

<build>
  ...
  <plugins>
    ...
    <plugin>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-maven-plugin</artifactId>
      <version>2.2.4.RELEASE</version>
      <executions>
        <execution>
          <goals>
            <goal>repackage</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
    ...
  </plugins>
  ...
</build>

The example above repackages a jar or war that is built during the package phase of the Maven lifecycle, including any provided dependencies that are defined in the project. If some of these dependencies need to be excluded, you can use one of the exclude options, see Exclude a dependency for more details. Please note that the outputFileNameMapping feature of the maven-war-plugin is currently not supported.

Devtools is automatically excluded by default (you can control that using the excludeDevtools property). In order to make that work with war packaging, the spring-boot-devtools dependency must be set as optional or with the provided scope.

The original (i.e. non executable) artifact is renamed to .original by default but it is also possible to keep the original artifact using a custom classifier.

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.

<build>
  ...
  <plugins>
    ...
    <plugin>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-maven-plugin</artifactId>
      <version>2.2.4.RELEASE</version>
      <configuration>
        <mainClass>${start-class}</mainClass>
        <layout>ZIP</layout>
      </configuration>
      <executions>
        <execution>
          <goals>
            <goal>repackage</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
    ...
  </plugins>
  ...
</build>

The layout property defaults to a guess based on the archive type (jar or war). The following layouts are available:

• JAR: regular executable JAR layout.
• WAR: executable WAR layout. provided dependencies are placed in WEB-INF/lib-provided to avoid any clash when the war is deployed in a servlet container.
• ZIP (alias to DIR): similar to the JAR layout using PropertiesLauncher.
• NONE: Bundle all dependencies and project resources. Does not bundle a bootstrap loader.

For more detailed examples of how to configure this goal see:

• Custom repackage classifier
• Exclude a dependency

Running the application

The plugin includes a run goal which can be used to launch your application from the command line:

mvn spring-boot:run

By default the application is executed in a forked process and setting properties on the command-line will not affect the application. If you need to specify some JVM arguments (i.e. for debugging purposes), you can use the jvmArguments parameter, see Debug the application for more details. There is also explicit support for system properties and environment variables.

As enabling a profile is quite common, there is dedicated profiles property that offers a shortcut for -Dspring-boot.run.jvmArguments="-Dspring.profiles.active=dev", see Specify active profiles.

Although this is not recommended, it is possible to execute the application directly from the Maven JVM by disabling the fork property. Doing so means that the jvmArguments, systemPropertyVariables, environmentVariables and agents options are ignored.

Spring Boot 1.3 has introduced devtools, a module to improve the development-time experience when working on Spring Boot applications. To enable it, just add the following dependency to your project:

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
    <version>2.2.4.RELEASE</version>
    <optional>true</optional>
  </dependency>
</dependencies>

When devtools is running, it detects change when you recompile your application and automatically refreshes it. This works for not only resources but code as well. It also provides a LiveReload server so that it can automatically trigger a browser refresh whenever things change.

Devtools can also be configured to only refresh the browser whenever a static resource has changed (and ignore any change in the code). Just include the following property in your project:

spring.devtools.remote.restart.enabled=false

Prior to devtools, the plugin supported hot refreshing of resources by default which has now be disabled in favour of the solution described above. You can restore it at any time by configuring your project:

<build>
  ...
  <plugins>
    ...
    <plugin>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-maven-plugin</artifactId>
      <version>2.2.4.RELEASE</version>
      <configuration>
        <addResources>true</addResources>
      </configuration>
    </plugin>
    ...
  </plugins>
  ...
</build>

When addResources is enabled, any src/main/resources folder will be added to the application classpath when you run the application and any duplicate found in target/classes will be removed. This allows hot refreshing of resources which can be very useful when developing web applications. For example, you can work on HTML, CSS or JavaScript 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.

Note that a side effect of using this feature is that filtering of resources at build time will not work.

In order to be consistent with the repackage goal, the run goal builds the classpath in such a way that any dependency that is excluded in the plugin's configuration gets excluded from the classpath as well. See Exclude a dependency for more details.

Sometimes it is useful to include test dependencies when running the application. For example, if you want to run your application in a test mode that uses stub classes. If you wish to do this, you can set the useTestClasspath parameter to true. Note that this is only applied when you run an application: the repackage goal will not add test dependencies to the resulting JAR/WAR.

Working with integration tests

While you may start your Spring Boot application very easily from your test (or test suite) itself, it may be desirable to handle that in the build itself. To make sure that the lifecycle of your Spring Boot application is properly managed around your integration tests, you can use the start and stop goals as described below:

<build>
  ...
  <plugins>
    ...
    <plugin>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-maven-plugin</artifactId>
      <version>2.2.4.RELEASE</version>
      <executions>
        <execution>
          <id>pre-integration-test</id>
          <goals>
            <goal>start</goal>
          </goals>
        </execution>
        <execution>
          <id>post-integration-test</id>
          <goals>
            <goal>stop</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
    ...
  </plugins>
  ...
</build>

Such setup can now use the failsafe-plugin to run your integration tests as you would expect.

You could also configure a more advanced setup to skip the integration tests when a specific property has been set:

<properties>
  <it.skip>false</it.skip>
</properties>
<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-failsafe-plugin</artifactId>
      <configuration>
        <skip>${it.skip}</skip>
      </configuration>
    </plugin>
    <plugin>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-maven-plugin</artifactId>
      <version>2.2.4.RELEASE</version>
      <executions>
        <execution>
          <id>pre-integration-test</id>
          <goals>
            <goal>start</goal>
          </goals>
          <configuration>
            <skip>${it.skip}</skip>
          </configuration>
        </execution>
        <execution>
          <id>post-integration-test</id>
          <goals>
            <goal>stop</goal>
          </goals>
          <configuration>
            <skip>${it.skip}</skip>
          </configuration>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>

If you run mvn verify -Dit.skip=true your integration tests will be skipped altogether.

For more detailed examples of how to configure this goal see:

• Random port for integration tests