code: public Boolean md5(Map<String, String> notifyParams){
          Map<String, String> validParams = filterSigningParams(notifyParams);
          String signing = buildSignString(validParams);
          String signed = md5(signing);
          return Objects.equals(notifyParams.get(AlipayField.SIGN.field()), signed);
      }
docs: MD5验证通知参数签名是否合法(WEB，WAP，退款服务器通知)
  @param notifyParams 通知参数
  @return 合法返回true，反之false