ASP.NET检测远程URL是否存在的几种方法

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("<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, "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;
  }
}