public Map<Partition, List<String>> getPartitionDescriptor(String streamName) {
    return partitionDescriptorMap.get(streamName);
  }
Get partition descriptors for a stream
@param streamName name of the stream; should contain the information about the path of the
                  root directory
@return map of the partition descriptor
samza-hdfs/src/main/java/org/apache/samza/system/hdfs/partitioner/DirectoryPartitioner.java