asp.net下检测远程URL是否存在的三种方法

代码如下:

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