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