一个在线用户列表统计程序

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Web;
using System.Web.Security;
using System.Web.SessionState;

namespace OnlineUser
{
    public class Global : System.Web.HttpApplication
    {

        protected void Application_Start(object sender, EventArgs e)
        {
            #region OnlineUsers

            try
            {
                DataTable userTable = new DataTable();
                userTable.Columns.Add("SessionID");
                userTable.Columns.Add("UserIP");
                userTable.Columns.Add("Browser");
                userTable.Columns.Add("OSName");
               
                userTable.AcceptChanges();
                Application.Lock();
                Application["OnlineUsers"] = userTable;
                Application.UnLock();
            }
            catch
            { }

            #endregion
        }

        protected void Session_Start(object sender, EventArgs e)
        {
            //用Cookie是为了防止同一个用户重复计数
            HttpCookie cookie = Request.Cookies["user"];
            if (null == cookie)//确定是否存在用户输入的cookie
            {           
                cookie = new HttpCookie("user");//创建一个名称是user的cookie对象
                cookie.Value = "used";//为该cookie赋值，只能是字符串，非字符串需转换
                cookie.Expires = DateTime.Now.AddHou