Usage

Some brief examples on how to use this plugin. If you want to use advanced configurations you should have a look at the documentation for Maven Archiver.

To handle archiving this version of Maven JAR Plugin uses Maven Archiver 2.5.

Note: Originally, this plugin was meant to sign JARs as well. As of version 2.3, the corresponding goals are no longer supported and users are advised to use the dedicated Maven Jarsigner Plugin instead.

How to build a JAR file

If the packaging of your project is set to 'jar', this plugin is executed whenever it passes the "package" phase. You can execute it using the command below:

mvn package

In your project's target directory you'll able to see the generated jar file.

How to include/exclude content from jar artifact

Specify a list of fileset patterns to be included or excluded by adding <includes>/<include> or <excludes>/<exclude> in your pom.xml.

<project>
  ...
  <build>
    <plugins>
      ...
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-jar-plugin</artifactId>
        <version>2.4</version>
        <configuration>
          <includes>
            <include>**/service/*</include>
          </includes>
        </configuration>
      </plugin>
      ...
    </plugins>
  </build>
  ...
</project>

Note that the patterns need to be relative to the path specified for the plugin's classesDirectory parameter.

How to create an additional attached jar artifact from the project

Specify a list of fileset patterns to be included or excluded by adding <includes>/<include> or <excludes>/<exclude> and add a classifier in your pom.xml.

Note: the jar-plugin must be defined in a new execution, otherwise it will replace the default use of the jar-plugin instead of adding a second artifact. The classifier is also required to create more than one artifact.

<project>
  ...
  <build>
    <plugins>
      ...
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-jar-plugin</artifactId>
        <version>2.4</version>
        <executions>
          <execution>
            <phase>package</phase>
            <goals>
              <goal>jar</goal>
            </goals>
            <configuration>
              <classifier>client</classifier>
              <includes>
                <include>**/service/*</include>
              </includes>
            </configuration>
          </execution>
        </executions>
      </plugin>
      ...
    </plugins>
  </build>
  ...
</project>

How to create a jar containing test classes

When you want to create a jar containing test-classes, you would probably want to reuse those classes. There are two ways to solve this:

  • Create an attached jar with the test-classes from the current project and loose its transitive test-scoped dependencies.
  • Create a separate project with the test-classes.

The easy way

You can produce a jar which will include your test classes and resources.

<project>
  ...
  <build>
    <plugins>
      ...
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-jar-plugin</artifactId>
        <version>2.4</version>
        <executions>
          <execution>
            <goals>
              <goal>test-jar</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
      ...
    </plugins>
  </build>
  ...
</project>

To reuse this artifact in an other project, you must declare this dependency with classifier test-jar :

<project>
  ...
  <dependencies>
    <dependency>
      <groupId>groupId</groupId>
      <artifactId>artifactId</artifactId>
      <type>test-jar</type>
      <version>version</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
  ...
</project>

Note: The downside of this solution is that you don't get the transitive test-scoped dependencies automatically. Maven only resolves the compile-time dependencies, so you'll have to add all the other required test-scoped dependencies by hand.

The preferred way

In order to let Maven resolve all test-scoped transitive dependencies you should create a separate project.

<project>
   <groupId>groupId</groupId>
    <artifactId>artifactId-tests</artifactId>
    <version>version</version>
  ...
</project>
  • Move the sources files from src/test/java you want to share from the original project to the src/main/java of this project. The same type of movement counts for the resources as well of course.
  • Move the required test-scoped dependencies and from the original project to this project and remove the scope (i.e. changing it to the compile-scope). And yes, that means that the junit dependency (or any other testing framework dependency) gets the default scope too. You'll probably need to add some project specific dependencies as well to let it all compile again.

Now you have your reusable test-classes and you can refer to it as you're used to:

<project>
  ...
  <dependencies>
    <dependency>
      <groupId>groupId</groupId>
      <artifactId>artifactId-tests</artifactId>
      <version>version</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
  ...
</project>

For full documentation, click here.