WebClient mywebclient = new WebClient();
        byte[] bytes = mywebclient.DownloadData("http://seasoncoffee.cn.alibaba.com/athena/contact/seasoncoffee.html");

 /// <summary>
    /// 访问网络上的文件HTML
    /// </summary>
    /// <param name="url"></param>
    /// <returns></returns>
    public static byte[] webRequestByte(string url) {

        WebRequest request = WebRequest.Create(url);
        WebResponse response = request.GetResponse();
        Stream resStream = response.GetResponseStream();  
        int bytelength=(int)response.ContentLength;
        Byte[] bytevalue = new Byte[bytelength];
       // resStream.Read(bytevalue, 0, bytevalue.Length);  
        int num=0;
        int m;
        while (1 > 0)
        {
            m = resStream.Read(bytevalue, num, bytelength);
            if(m==0)break;
            num += m;           //当前已下载的字节数
            bytelength -= m;    //剩余字节数   总字节数：(int)response.ContentLength                            
        }
        resStream.Close();

        return bytevalue;

       // StreamReader sr = new StreamReader(resStream, System.Text.Encoding.Default);  //转换成字符串 输出
      //  ContentHtml.Text = sr.ReadToEnd();
        // sr.Close();

        //WebClient 得到字节流
        //WebClient wc=new WebClient();
        // Stream srm=wc.OpenRead(TempDown);
        
        //区别在于  WebRequest 是 system.net 空间下的 抽象类,你可以对它进行扩展
        //WebClient 非抽象类

    }