code: public static String failedJson(int code, String message) {
          ReturnData returnData = new ReturnData();
          returnData.setSuccess(false);
          returnData.setErrorCode(code);
          returnData.setErrorMsg(message);
          return JSON.toJSONString(returnData);
      }
docs: Business is failed.
  
  @param code error code.
  @param message message.
  
  @return json.