C# post方法

/// <summary>
        /// post方法
        /// </summary>
        /// <param name="url">服务器URL</param>
        /// <param name="param">要发送的参数字符串</param>
        /// <returns>服务器返回字符串</returns>
        public static string postSend(string url, string param, string contentType = "application/json;charset=UTF-8")
        {
            System.Text.Encoding myEncode = System.Text.Encoding.GetEncoding("UTF-8");
            byte[] postBytes = System.Text.Encoding.UTF8.GetBytes(param);


            HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(url);
            req.Method = "POST";
            req.ContentType = contentType;//x-www-form-urlencoded
            req.ContentLength = postBytes.Length;
            try
            {
                using (Stream reqStream = req.GetRequestStream())
                {
                    reqStream.Write(postBytes, 0, postBytes.Length);
                }

                using (WebResponse res = req.GetResponse())
                {
                    using (StreamReader sr = new StreamReader(res.GetResponseStream(), myEncode))
                    {
                        string strResult = sr.ReadToEnd();
                        return strResult;
                    }
                }

            }
            catch (WebException ex)
            {
                throw ex;
            }
            catch (Exception ex)
            {
                return ex.Message;
            }

        }