private void Page_Load(object sender, System.EventArgs e)
{

string url1 = "http://csharp.xdowns.com";
string url2 = "http://csharp.xdowns.com/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;
}
}


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