判断远程文件是否存在

　　　　 /// <summary>
        /// 判断远程文件是否存在
        /// </summary>
        /// <param name="url">url地址</param>
        /// <returns></returns>
        public bool FileExists(string url)
        {
            //ture为存在，false为不存在
            bool result = false;
            WebResponse response = null;
            try
            {
                WebRequest req = WebRequest.Create(url);
                response = req.GetResponse();
                result = response == null ? false : true;
            }
            catch (Exception ex)
            {
                result = false;
            }
            finally
            {
                if (response != null)
                {
                    response.Close();
                }
            }
            return result;
        }