WebClient模拟发送Post请求

        /// <summary>
        /// 模拟post请求
        /// </summary>
        /// <param name="Url"></param>
        /// <param name="postDataStr"></param>
        /// <returns></returns>
        private string HttpPost(string Url, string postDataStr)
        {
            byte[] bytes = Encoding.UTF8.GetBytes(postDataStr);
            WebClient client = new WebClient();
            client.Headers.Add("Content-Type", "application/x-www-form-urlencoded");
            client.Headers.Add("ContentLength", postDataStr.Length.ToString());
            byte[] responseData = client.UploadData(Url, "POST", bytes);
            string retString = Encoding.UTF8.GetString(responseData);
            return retString;
        }

string postDataStr = "userId=" + userId + "&sig=" + sigStr;
string jsonStr = HttpPost("http://www.xx/query.json", postDataStr); //返回utf8的JSON