public HdfsOutputDescriptor getOutputDescriptor(String streamId) {
    return new HdfsOutputDescriptor(streamId, this);
  }
Gets an {@link HdfsOutputDescriptor} for the output stream of this system.
<p>
The message in the stream has no key and the value type is determined by writer class.

@param streamId id of the output stream
@return an {@link HdfsOutputDescriptor} for the hdfs output stream
samza-hdfs/src/main/java/org/apache/samza/system/hdfs/descriptors/HdfsSystemDescriptor.java