code: public static boolean checkParam(Map<String, String> params, String key) {
          boolean result = false;
          if (params.containsKey("sign")) {
              String sign = params.get("sign");
              params.remove("sign");
              StringBuilder buf = new StringBuilder((params.size() + 1) * 10);
              SignUtils.buildPayParams(buf, params, false);
              String preStr = buf.toString();
              String signReceive = MD5Utils.sign(preStr, "&key=" + key, "utf-8");
              result = sign.equalsIgnoreCase(signReceive);
          }
          return result;
      }
docs: 验证返回参数
  
  @param params
  @param key
  @return