asp.net(c#)判断远程图片是否存在

privateintGetUrlError(stringcurl)
{
intnum=200;
if(this.method==1)
{
HttpWebRequestrequest=(HttpWebRequest)WebRequest.Create(newUri(curl));
ServicePointManager.Expect100Continue=false;
try
{
((HttpWebResponse)request.GetResponse()).Close();
}
catch(WebExceptionexception)
{
if(exception.Status!=WebExceptionStatus.ProtocolError)
{
returnnum;
}
if(exception.Message.IndexOf("500")>0)
{
return500;
}
if(exception.Message.IndexOf("401")>0)
{
return401;
}
if(exception.Message.IndexOf("404")>0)
{
num=404;
}
}
returnnum;
}
}