@Override
  public AlterTableMessage buildAlterTableMessage(Table before, Table after, Long writeId) {
    return new JSONAlterTableMessage(HCAT_SERVER_URL, HCAT_SERVICE_PRINCIPAL, before.getDbName(),
        before.getTableName(), before.getTableType(), writeId, now());
  }
The JSON implementation of the MessageFactory. Constructs JSON implementations of
each message-type.
hcatalog/server-extensions/src/main/java/org/apache/hive/hcatalog/messaging/json/JSONMessageFactory.java