Application_Error中判断404错误状态

void Application_Error(object sender, EventArgs e)
{
    Exception ex = Server.GetLastError();
    if (ex is HttpException)
    {
        if (((HttpException)(ex)).GetHttpCode() == 404)
            Server.Transfer("~/Error404.aspx");
    }
    // Code that runs when an unhandled error occurs
    Server.Transfer("~/DefaultError.aspx");
}