/*
    *  url:POST请求地址
    *  postData:json格式的请求报文,例如：{"key1":"value1","key2":"value2"}
    */

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

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

            req.Method = "POST";

            req.TimeOut = "800";//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();

            Stream stream = resp.GetResponseStream();

            //获取响应内容
            using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))
            {
                result = reader.ReadToEnd();
            }

            return result;
        }