C# post 提交 application/json 类型数据

     public static string PostJson(string url, string jsonParam,string encode) 
        {
            string strURL = url;
            System.Net.HttpWebRequest request;
            request = (System.Net.HttpWebRequest)WebRequest.Create(strURL);
            request.Method = "POST";
            request.ContentType = "application/json;charset="+encode.ToUpper();
            string paraUrlCoded = jsonParam;
            byte[] payload;
            payload = System.Text.Encoding.GetEncoding(encode.ToUpper()).GetBytes(paraUrlCoded);
            request.ContentLength = payload.Length;
            Stream writer = request.GetRequestStream();
            writer.Write(payload, 0, payload.Length);
            writer.Close();
            System.Net.HttpWebResponse response;
            response = (System.Net.HttpWebResponse)request.GetResponse();
            System.IO.Stream s;
            s = response.GetResponseStream();
            string StrDate = "";
            string strValue = "";
            StreamReader Reader = new StreamReader(s, Encoding.GetEncoding(encode.ToUpper()));
            while ((StrDate = Reader.ReadLine()) != null)
            {
                strValue += StrDate + "\r\n";
            }
            return strValue;
        }