检测远程URL是否存在的三种方法

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 = "http://dotnet.aspx.cc/Images/logo.gif";
 Response.Write("

• 方法1：");
   Response.Write(url1 + " 存在：" + UrlExistsUsingHttpWebRequest(url1).ToString());
   Response.Write("
• 方法2：");
   Response.Write(url1 + " 存在：" + UrlExistsUsingSockets(url1).ToString());   
   Response.Write("
• 方法3：");
   Response.Write(url1 + " 存在：" + UrlExistsUsingXmlHttp(url1).ToString());

   Response.Write("

• 方法1：");
   Response.Write(url2 + " 存在：" + UrlExistsUsingHttpWebRequest(url2).ToString());
   Response.Write("
• 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,"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;
   }
  }