public void GetResponse(string url, string json)
{

        Encoding encoding = Encoding.UTF8;
        byte[] data = encoding.GetBytes( json );
        //此处为为http请求url 
        var uri = new Uri( url );
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create( uri );
        //此处为C#实现的一些标准http请求头添加方法，用上面的方面也可以实现 
        request.ContentType = "application/json";
        request.Accept = "application/json";
        // request.ContentLength = data.Length; 
        //此处添加标准http请求方面 
        request.Method = "POST";
        System.IO.Stream sm = request.GetRequestStream();
        sm.Write( data, 0, data.Length );
        sm.Close();
        HttpWebResponse response = (HttpWebResponse)request.GetResponse();
        Stream streamResponse = response.GetResponseStream();
        StreamReader streamRead = new StreamReader( streamResponse, Encoding.UTF8 );
        Char[] readBuff = new Char[256];
        int count = streamRead.Read( readBuff, 0, 256 );
        //content为http响应所返回的字符流 
        String content = "";
        while (count > 0)
        {
            String outputData = new String( readBuff, 0, count );
            content += outputData;
            count = streamRead.Read( readBuff, 0, 256 );
        }
        response.Close();
    }

我想给指定的地址发送一段json数据，但是一直失败