public static MessageEncoder getInstance() {
    if (instance == null) {
      synchronized (GzipJSONMessageEncoder.class) {
        if (instance == null) {
          instance = new JSONMessageEncoder();
        }
      }
    }
    return instance;
  }
The JSON implementation of the MessageFactory. Constructs JSON implementations of each
message-type.
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/messaging/json/JSONMessageEncoder.java