本文用3种方法检测远程URL是否存在。 示例代码如下：
//第一种方法 private void Page_Load(object sender, System.EventArgs e) 
...{ 
string url1 = "http://www.aspxcs.net/"; string url2 = "http://www.aspxcs.net/aspxcs.gif"; Response.Write("<li>方法1："); Response.Write(url1 + " 存在：" + UrlExistsUsingHttpWebRequest(url1).ToString()); Response.Write("<li>方法2："); Response.Write(url1 + " 存在：" + UrlExistsUsingSockets(url1).ToString()); Response.Write("<li>方法3："); Response.Write(url1 + " 存在：" + UrlExistsUsingXmlHttp(url1).ToString()); Response.Write("<li>方法1："); Response.Write(url2 + " 存在：" + UrlExistsUsingHttpWebRequest(url2).ToString()); Response.Write("<li>方法3："); Response.Write(url2 + " 存在：" + UrlExistsUsingXmlHttp(url2).ToString()); 
} //第二种方法 
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; } } //第三种方法 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); } 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; } 
}