@org.apache.thrift.annotation.Nullable
    public static _Fields findByThriftId(int fieldId) {
      switch(fieldId) {
        case 1: // START_TIME
          return START_TIME;
        case 2: // PROCESSING_TIME
          return PROCESSING_TIME;
        case 3: // QUEUE_TIME
          return QUEUE_TIME;
        case 4: // RESPONSE_SIZE
          return RESPONSE_SIZE;
        case 5: // CLIENT_ADDRESS
          return CLIENT_ADDRESS;
        case 6: // SERVER_CLASS
          return SERVER_CLASS;
        case 7: // METHOD_NAME
          return METHOD_NAME;
        case 8: // CALL_DETAILS
          return CALL_DETAILS;
        case 9: // PARAM
          return PARAM;
        case 10: // USER_NAME
          return USER_NAME;
        case 11: // MULTI_GETS_COUNT
          return MULTI_GETS_COUNT;
        case 12: // MULTI_MUTATIONS_COUNT
          return MULTI_MUTATIONS_COUNT;
        case 13: // MULTI_SERVICE_CALLS
          return MULTI_SERVICE_CALLS;
        case 14: // REGION_NAME
          return REGION_NAME;
        case 15: // BLOCK_BYTES_SCANNED
          return BLOCK_BYTES_SCANNED;
        case 16: // FS_READ_TIME
          return FS_READ_TIME;
        default:
          return null;
      }
    }
Find the _Fields constant that matches fieldId, or null if its not found.
hbase-thrift/src/main/java/org/apache/hadoop/hbase/thrift2/generated/TOnlineLogRecord.java