public static string PostUrl(string url, string postData)        {            string result = "";

            HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);

            req.Method = "POST";

            req.TimeOut = "30000";//设置请求超时时间，单位为毫秒

            req.ContentType = "application/json";

            byte[] data = Encoding.UTF8.GetBytes(postData);

            req.ContentLength = data.Length;

            using (Stream reqStream = req.GetRequestStream())            {                reqStream.Write(data, 0, data.Length);

                reqStream.Close();            }

            HttpWebResponse resp = (HttpWebResponse)req.GetResponse();