C# httpwebrequest的POST提交

 private string PostWebRequest(string postUrl, string paramData, Encoding dataEncode)
        {
            string ret = string.Empty;
            try
            {
                byte[] byteArray = Encoding.Default.GetBytes(paramData); //转化
                HttpWebRequest webReq = (HttpWebRequest)WebRequest.Create(new Uri(postUrl));
                webReq.Method = "POST";
                webReq.ContentType = "application/x-www-form-urlencoded";
                webReq.Timeout = 10000;
                webReq.CookieContainer = cookie;//传入cookie
                webReq.ContentLength = byteArray.Length;
                Stream newStream = webReq.GetRequestStream();
                newStream.Write(byteArray, 0, byteArray.Length);//写入参数
                newStream.Close();
                HttpWebResponse response = (HttpWebResponse)webReq.GetResponse();
                StreamReader sr = new StreamReader(response.GetResponseStream(), Encoding.Default);
                ret = sr.ReadToEnd();
                sr.Close();
                response.Close();
                newStream.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            return ret;
        }