Building a runnable jar with maven 2

Question

I'm relatively new to the maven mantra, but I'm trying to build a command-line runnable jar with maven. I've setup my dependencies, but when I run mvn install and attempt to run the jar, two things happen. First, no main class is found, which is correctable. When I've corrected this, I get errors on run stating that classes cannot be found.

Maven is not packaging my dependency libraries inside of the jar, so I am unable to run the jar as a stand-alone application. How do I correct this?

Answer 1

Maven is not packaging your dependencies inside your jar file, because you don't usually do this with Java programs.

Instead you deliver the dependencies together with your jar file and mention them in the Class-Path header of the Manifest.

To go this route, you'll need to enable the addClasspath property (documented here) for the maven-jar-plugin as shown by Bozho.

If you really want to include all your dependencies in your jar file, then you can use the Maven Assembly plugin to create a jar-with-dependencies.

Answer 2

The easiest way to do this would be to create an assembly using the maven-assembly-plugin and the predefined jar-with-dependencies descriptor. You'll also need to generate a manifest with a main-class entry for this uber jar. The snippet below shows how to configure the assembly plugin to do so:

<build>
  <plugin>
    <plugin>
      <artifactId>maven-assembly-plugin</artifactId>
      <configuration>
        <descriptorRefs>
          <descriptorRef>jar-with-dependencies</descriptorRef>
        </descriptorRefs>
        <archive>
          <manifest>
            <mainClass>fully.qualified.MainClass</mainClass>
          </manifest>
        </archive>
      </configuration>
    </plugin>
  </plugins>
</build>

Then, to generate the assembly, just run:

mvn assembly:assembly

If you want to generate the assembly as part of your build, simply bind the assembly:single mojo to the package phase:

<build>
  <plugin>
    <plugin>
      <artifactId>maven-assembly-plugin</artifactId>
      <configuration>
        <descriptorRefs>
          <descriptorRef>jar-with-dependencies</descriptorRef>
        </descriptorRefs>
        <archive>
          <manifest>
            <mainClass>fully.qualified.MainClass</mainClass>
          </manifest>
        </archive>
      </configuration>
      <executions>
        <execution>
          <phase>package</phase>
          <goals>
            <goal>single</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>

And simply run:

mvn package