@Override
  public boolean isWriteable(Class<?> arg0, Type arg1, Annotation[] arg2, MediaType arg3) {
    return true;
  }
An adapter between Jersey and Object.toString(). Hooks up plain text output to the Jersey content
handling framework. Jersey will first call getSize() to learn the number of bytes that will be
sent, then writeTo to perform the actual I/O.
hbase-rest/src/main/java/org/apache/hadoop/hbase/rest/provider/producer/PlainTextMessageBodyProducer.java