WebRequest发送请求并接收返回值

public string getXmlStr(string hphmcode)
        {
            string Url = "http://localhost:8080/readvioinfo.jsp";
            string hphm = hphmcode;
            string hpzl = "02";
            //Encoding encoding = Encoding.GetEncoding("utf-8");
            Encoding encoding = Encoding.GetEncoding("GB2312");
             string postData = "hphm=" + hphm + "&hpzl=" + hpzl;
            byte[] data = encoding.GetBytes(postData);
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url);
            //发送数据
            request.Method = "POST";
            request.ContentType = "application/x-www-form-urlencoded";
            request.ContentLength = data.Length;
            Stream requestStream = request.GetRequestStream();
            requestStream.Write(data, 0, data.Length);
            requestStream.Close();
            //接收返回值
            HttpWebResponse res = (HttpWebResponse)request.GetResponse();
            StreamReader sReader = new StreamReader(res.GetResponseStream(), System.Text.Encoding.UTF8);
            string strBack = sReader.ReadToEnd();
            //Response.Write(strBack);
            sReader.Close();
            res.Close();
            return strBack;
        }