private static string getHtml(string url, string charSet)//url是要访问的网站地址，charSet是目标网页的编码，如果传入的是null或者""，那就自动分析网页的编码 
        {
            charSet = "gb2312";
            WebClient myWebClient = new WebClient(); //创建WebClient实例myWebClient 
            // 需要注意的： 
            //有的网页可能下不下来，有种种原因比如需要cookie,编码问题等等 
            //这是就要具体问题具体分析比如在头部加入cookie 
            // webclient.Headers.Add("Cookie", cookie); 
            //这样可能需要一些重载方法。根据需要写就可以了 
            //获取或设置用于对向 Internet 资源的请求进行身份验证的网络凭据。 
            myWebClient.Credentials = CredentialCache.DefaultCredentials;
            //如果服务器要验证用户名,密码 
            //NetworkCredential mycred = new NetworkCredential(struser, strpassword); 
            //myWebClient.Credentials = mycred; 
            //从资源下载数据并返回字节数组。（加@是因为网址中间有"/"符号） 
            byte[] myDataBuffer = myWebClient.DownloadData(url);
            string strWebData = Encoding.GetEncoding("GB2312").GetString(myDataBuffer);
            //StreamWriter sw = new StreamWriter("D:/qq-utf-8.txt");
            //sw.Write(strWebData);
            //sw.Close();
            //获取网页字符编码描述信息 
            Match charSetMatch = Regex.Match(strWebData, "<meta([^<]*)charset=([^<]*)\"", RegexOptions.IgnoreCase | RegexOptions.Multiline);
            string webCharSet = charSetMatch.Value;

            int start = webCharSet.IndexOf("charset=");
            
            //if (start == -1)
            //{
            //    charSet = "utf-8";
            //    strWebData = Encoding.GetEncoding(charSet).GetString(myDataBuffer);
            //    charSetMatch = Regex.Match(strWebData, "<meta([^<]*)charset=([^<]*)\"", RegexOptions.IgnoreCase | RegexOptions.Multiline);
            //    webCharSet = charSetMatch.Value;
            //    start = webCharSet.IndexOf("charset=");
            //}
            int end = webCharSet.IndexOf("\"", start);
            webCharSet=webCharSet.Substring(start+8,end-(start+8));
            if(webCharSet!=charSet)
                strWebData = Encoding.GetEncoding(webCharSet).GetString(myDataBuffer);
            //if (charSet == null || charSet == "")
            //    charSet = webCharSet;
            
            //if (charSet != null && charSet != "" && Encoding.GetEncoding(charSet) != Encoding.GetEncoding("utf-8"))
            //    strWebData = Encoding.GetEncoding(charSet).GetString(myDataBuffer);
            return strWebData;
        }