code: public String ok(){
          Map<String, String> notifyParams = new HashMap<>();
          notifyParams.put(WepayField.RETURN_CODE, "SUCCESS");
          notifyParams.put(WepayField.RETURN_MSG, "OK");
          return Maps.toXml(notifyParams);
      }
docs: 通知成功
  @return 通知成功的XML消息