javamaven-2build-processexecutable-jar

Building a runnable jar with Maven 2


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?


Solution

  • 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>
      <plugins>
        <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>
      <plugins>
        <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