code: public synchronized Set<Artifact> getArtifacts( String groupId, String artifactId, String version )
      {
          String path = groupId.replace( '.', '/' ) + '/' + artifactId + "/" + version;
          Map<String, Artifact> artifactMapper = this.children.get( path );
          if ( artifactMapper == null )
          {
              return Collections.emptySet();
          }
          Set<Artifact> result = new HashSet<Artifact>();
          for ( Artifact a : artifactMapper.values() )
          {
              if ( a != null )
              {
                  result.add( a );
              }
          }
          return result;
      }
docs: {@inheritDoc}