/// <summary>
/// 获取Response.Redirect重定向后的URL
/// </summary>
/// <param name="url"></param>
/// <returns></returns>
/// <remarks>
/// using System.IO;
/// using System.Net;
/// </remarks>
static string GetRealUrl(string url)
{
    Uri uri = new Uri(url);
    HttpWebRequest webRequest = (HttpWebRequest)HttpWebRequest.Create(uri);
    webRequest.AllowAutoRedirect = false;
    HttpWebResponse webResponse;
    string realurl = string.Empty;

    try
    {
        webResponse = (HttpWebResponse)webRequest.GetResponse();//404 WebException
        realurl = webResponse.Headers["Location"];

        if (realurl.Length < 7 || (realurl.Length >= 7 && realurl.Substring(0, 7) != "http://"))
        {
            Console.WriteLine("Yes");
            if (realurl.Substring(0, 1) == "/")//绝对路径
            {
                realurl = string.Format("http://{0}{1}", uri.Authority, realurl);
            }
            else//相对路径
            {
                realurl = string.Format("http://{0}{1}", uri.Authority, uri.AbsolutePath.Replace(Path.GetFileName(uri.AbsolutePath), realurl));
            }
        }

    }
    catch { }

    return realurl;
}