using System.IO;

protected void Application_Start(object sender, EventArgs e)

        {

            FileStream fs = File.Open(Server.MapPath("counter.txt"),FileMode.OpenOrCreate);

            StreamReader sr = new StreamReader(fs);

            Application["count"] = Convert.ToInt32(sr.ReadLine());

            sr.Close();

            fs.Close();

        }

//counter.txt会自动创建

        protected void Session_Start(object sender, EventArgs e)

        {

            Application.Lock();

            Application["count"] = (int)Application["count"] + ;

            FileStream fs = File.Open(Server.MapPath("counter.txt"), FileMode.OpenOrCreate,FileAccess.ReadWrite);

            StreamWriter sw = new StreamWriter(fs);

            sw.WriteLine(Application["count"]);

            sw.Close();

            fs.Close();

            Application.UnLock();

        }