用c#判断远程文件是否存在

public static 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;
}
}
}

//2:

private bool UrlExistsUsingXmlHttp(string url)
{
//注意：此方法需要引用Msxml2.dll
MSXML2.XMLHTTP _xmlhttp = new MSXML2.XMLHTTPClass();
_xmlhttp.open("HEAD", url, false, null, null);
_xmlhttp.send("");
return (_xmlhttp.status == 200);
}

//3:
private bool UrlExistsUsingSockets(string url)
{
if (url.StartsWith("http://")) url = url.Remove(0, "http://".Length);
try
{
System.Net.IPHostEntry ipHost =System.Net.Dns.GetHostEntry(url);// System.Net.Dns.Resolve(url);
return true;
}
catch (System.Net.Sockets.SocketException se)
{
System.Diagnostics.Trace.Write(se.Message);
return false;
}
}