code: public Set<String> getArtifactIds( String groupId )
      {
          File groupDir = new File( root, groupId.replace( '.', '/' ) );
          if ( !groupDir.isDirectory() )
          {
              return Collections.emptySet();
          }
          Set<String> result = new HashSet<String>();
          File[] artifactDirs = groupDir.listFiles();
          for ( int i = 0; i < artifactDirs.length; i++ )
          {
              if ( !artifactDirs[i].isDirectory() )
              {
                  continue;
              }
              final String artifactId = artifactDirs[i].getName();
              result.add( artifactId );
          }
          return result;
      }
docs: {@inheritDoc}