本文用3种方法检测远程URL是否存在。

private void Page_Load(object sender, System.EventArgs e)

{

 string url1 = "http://dotnet.aspx.cc/";

 string url2 = "";

 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());

}

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)

{

 //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,");

 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;

 }

}