检测远程URL是否存在的三种方法

privatevoid Page_Load(object sender, System.EventArgs e)
{
     string url1 ="http://dotnet.aspx.cc/";
     string url2 ="http://dotnet.aspx.cc/Images/logo.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());
}

privatebool 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);
      returnfalse;
}
}

privatebool 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);
}
privatebool UrlExistsUsingSockets(string url)
{
          if (url.StartsWith("http://")) url = url.Remove(0, "http://".Length);
          try
          {       
              System.Net.IPHostEntry ipHost = System.Net.Dns.Resolve(url);
              returntrue;
           }
          catch (System.Net.Sockets.SocketException se)
          {
                 System.Diagnostics.Trace.Write(se.Message);
                returnfalse
          }
}