ASP.NET C# 判断页面是否存在，是否404错误，方法如下，调用方法即可

private static bool UrlIsExist(String url)

        {

            System.Uri u = null;

            try

                u = new Uri(url);

            }

            catch { return false; }

            bool isExist = false;

            System.Net.HttpWebRequest r = System.Net.HttpWebRequest.Create(u) as System.Net.HttpWebRequest;

            r.Method = "HEAD";

            try

                System.Net.HttpWebResponse s = r.GetResponse() as System.Net.HttpWebResponse;

                if (s.StatusCode == System.Net.HttpStatusCode.OK)

                {

                    isExist = true;

                }

            }

            catch (System.Net.WebException x)

                try

                {

                    isExist = ((x.Response as System.Net.HttpWebResponse).StatusCode != System.Net.HttpStatusCode.NotFound);

                }

                catch { isExist = (x.Status == System.Net.WebExceptionStatus.Success); }

            }

            return isExist;

        }