C# 根據網址下載網頁

/// 
/// 下載網頁
/// 
/// 網址
/// 文件路徑
public void DownloadFile(string URL, string filename)
{
start:
    HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(URL);
    req.Method = "GET";
    req.Timeout = 60000;
    req.KeepAlive = true;
    req.AllowAutoRedirect = true;
    HttpWebResponse rps = (HttpWebResponse)req.GetResponse();
    if (rps.StatusCode != HttpStatusCode.OK)
    {
        goto start;
    }
    Stream respStream = rps.GetResponseStream();
    using (StreamReader reader = new StreamReader(respStream, Encoding.GetEncoding("utf-8")))
    {
        //ReadToEnd方法不好使，有時候拋異常：無法從傳輸連接中讀取數據: 遠程主機強迫關閉了一個現有的連接
        //string text = reader.ReadToEnd(); 
        string text = string.Empty, line = string.Empty;
        while ((line = reader.ReadLine()) != null)
        {
            text += line;
        }
        reader.Close();
        FileStream fs = new FileStream(filename, FileMode.Append);
        StreamWriter sw = new StreamWriter(fs, Encoding.UTF8);
        sw.Write(text);
        sw.Close();
        fs.Close();
    }
}