c#检查网络文件是否存在

  public  bool IsExist(string uri)
        {
            HttpWebRequest req = null;
            HttpWebResponse res = null;
            try
            {
                req = (HttpWebRequest)WebRequest.Create(uri);
                req.Method = "HEAD";
                req.Timeout = 100;
                res = (HttpWebResponse)req.GetResponse();
                return (res.StatusCode == HttpStatusCode.OK);
            }
            catch
            {
                return false;
            }
            finally
            {
                if (res != null)
                {
                    res.Close();
                    res = null;
                }
                if (req != null)
                {
                    req.Abort();
                    req = null;
                }
            }
        }