C# 下载资源

//创建一个初始化请求对象
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(new Uri("http://wwww.baidu.com/m.mp3"));

                //设置下载相关参数  
                RequestState requestState = new RequestState();
                requestState.BUFFER_SIZE = 1024;
                requestState.BufferRead = new byte[requestState.BUFFER_SIZE];
                requestState.Request = request;
                requestState.SavePath = System.Web.HttpRuntime.AppDomainAppPath + FilePath;
                requestState.FileStream = new FileStream(requestState.SavePath, FileMode.OpenOrCreate);
                request.Headers.Add("media_id", media_id);
                request.Headers.Add("msgtype", MsgType);
                //开始异步请求资源  
                request.BeginGetResponse(new AsyncCallback(ResponseCallback), requestState);