Three ways to detect the existence of a remote URL under asp.net-practical tips

Copy Code code as follows:

private void Page_Load (object sender, System.EventArgs e)
{
String url1 = "http://s.jb51.net/";
String url2 = "Yun_qi_img/logo.gif";
Response.Write ("<li> Method 1:");
Response.Write (URL1 + "presence:" + urlexistsusinghttpwebrequest (URL1). ToString ());
Response.Write ("<li> Method 2:");
Response.Write (URL1 + "presence:" + urlexistsusingsockets (URL1). ToString ());
Response.Write ("<li> Method 3:");
Response.Write (URL1 + "presence:" + urlexistsusingxmlhttp (URL1). ToString ());
Response.Write ("<li> Method 1:");
Response.Write (Url2 + "presence:" + urlexistsusinghttpwebrequest (URL2). ToString ());
Response.Write ("<li> Method 3:");
Response.Write (Url2 + "presence:" + urlexistsusingxmlhttp (URL2). ToString ());
}

private bool Urlexistsusinghttpwebrequest (string URL) {
Try
{
System.Net.HttpWebRequest myrequest = (System.Net.HttpWebRequest) System.Net.WebRequest.Create (URL);
Myrequest.method = "Head";
myrequest.timeout = 100;
System.Net.HttpWebResponse res = (System.Net.HttpWebResponse) myrequest.getresponse ();
Return (Res. StatusCode = = System.Net.HttpStatusCode.OK);
}
catch (System.Net.WebException We)
{
System.Diagnostics.Trace.Write (We. message);
return false;
}
}

private bool Urlexistsusingxmlhttp (string URL)
{
Note: This method requires reference to Msxml2.dll
MSXML2. XMLHTTP _xmlhttp = new MSXML2. Xmlhttpclass ();
_xmlhttp.open ("Head", URL, false, NULL, NULL);
_xmlhttp.send ("");
return (_xmlhttp.status = 200);
}
private bool Urlexistsusingsockets (string URL)
{
if (URL. StartsWith ("http://")) url = URL. Remove (0, "http://". Length);
Try
{
System.Net.IPHostEntry iphost = System.Net.Dns.Resolve (URL);
return true;
}
catch (System.Net.Sockets.SocketException se)
{
System.Diagnostics.Trace.Write (SE. message);
return false;
}
}