@SuppressWarnings("unchecked")
  protected Message toMessage(Writable writable) {
    return ((ProtoMessageWritable<Message>)writable).getMessage();
  }
Class to convert ProtoMessageWritable to hive formats.
@see ProtobufSerDe
ql/src/java/org/apache/hadoop/hive/ql/io/protobuf/ProtobufMessageSerDe.java