private String eventMessageAsJSON(T eventMessage) {
    if (eventMessage == null) {
      // this will only happen in case DefaultHandler is invoked
      return null;
    }
    return jsonMessageEncoder.getSerializer().serialize(eventMessage);
  }
This takes in the string representation of the message in the format as specified in rdbms backing metastore.
ql/src/java/org/apache/hadoop/hive/ql/parse/repl/dump/events/AbstractEventHandler.java