code: public File createArchive()
          throws MojoExecutionException
      {
          File jarFile = getJarFile( outputDirectory, finalName, getClassifier() );
  
          MavenArchiver archiver = new MavenArchiver();
  
          archiver.setArchiver( jarArchiver );
  
          archiver.setOutputFile( jarFile );
  
          archive.setForced( forceCreation );
  
          try
          {
              File contentDirectory = getClassesDirectory();
              if ( !contentDirectory.exists() )
              {
                  getLog().warn( "JAR will be empty - no content was marked for inclusion!" );
              }
              else
              {
                  archiver.getArchiver().addDirectory( contentDirectory, DEFAULT_INCLUDES, DEFAULT_EXCLUDES );
              }
  
              archiver.createArchive(mavenSession, project, archive);
  
              return jarFile;
          }
          catch ( Exception e )
          {
              throw new MojoExecutionException( "Error assembling JAR", e );
          }
      }
docs: Generates the JAR.
  
  @return a {@link java.io.File} object.
  @throws org.apache.maven.plugin.MojoExecutionException if any.