判断远程文件是否存在

此处用到：System.Net命名空间

// string url是文件路径，如：[url]http://www.xxx.com/abc.xml  [/url]
            
             try
            {
                HttpWebRequest re = (HttpWebRequest)WebRequest.Create(url);
                HttpWebResponse res = (HttpWebResponse)re.GetResponse();
                 if (res.ContentLength!=0)
                {
                    MessageBox.Show( "文件存在");
                }
            }
             catch (Exception)
            {
                MessageBox.Show( "无此文件");
                 return;
            }