c# webrequest访问网页

using System;
using System.Collections.Generic;
using System.Text;
using System.Net;
using System.IO;

namespace spider
{
    class Program
    {
        static void Main(string[] args)
        {
            string html = null;
            string url = "http://china.alibaba.com/keyword/promotion.htm?catId=14";
            WebRequest req = WebRequest.Create(url);
            WebResponse res = req.GetResponse();
            Stream receiveStream = res.GetResponseStream();
            Encoding encode = Encoding.GetEncoding("gb2312");
            StreamReader sr = new StreamReader(receiveStream, encode);
            char[] readbuffer = new char[256];
            int n = sr.Read(readbuffer, 0, 256);
            while (n > 0)
            {
                string str = new string(readbuffer, 0, n);
                html += str;
                n = sr.Read(readbuffer, 0, 256);
            }
            System.Console.Write(html);
        }
    }
}