asp.net下检测远程URL是否存在的三种方法

private void Page_Load(object sender, System.EventArgs e)
{
string url1 = "http://s.jb51.net/";
string url2 = "https://www.jb51.net/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;
}
}