Hashtable h = (Hashtable)Application["online"];
if (h[Session.SessionID] != null)
h.Remove(Session.SessionID);
Application["online"] = h;

sessionState mode="InProc">/sessionState>

private void isLogin()
{
Hashtable h = (Hashtable)Application["online"];

if (h == null)
{
h = new Hashtable();
}

//驗(yàn)證用戶是否在Application中存在(是否在線)
IDictionaryEnumerator e1 = h.GetEnumerator();
bool flag = false;
while (e1.MoveNext())
{
if (checkCookie(e1.Value.ToString()))
{
flag = true;
break;
}
}
if (flag)
{
Response.Write("script defer language='javascript'>alert('This user is online!');history.go(-1);/script>");
}
else
{
loginLogic login = new loginLogic(this.txt_user_id.Text.Trim(), this.txt_password.Text.Trim());

if (!login.getLoginStatus)
{
Response.Write("script defer language='javascript'>alert('Invalid UserID or password.Please try again.');/script>");
}
else
{
//生成服務(wù)端標(biāo)識(shí)值
DateTime now = DateTime.Now;
string cookieValue = now.Year.ToString() + now.Month.ToString() + now.Day.ToString() + now.Hour.ToString() + now.Minute.ToString() + now.Second.ToString() + now.Millisecond.ToString();
//把userid + 標(biāo)識(shí)值寫入全局變量表
h[Session.SessionID] = this.txt_user_id.Text.Trim() + "-" + cookieValue;
Application["Online"] = h;
//把標(biāo)識(shí)值寫入客戶端cookie
Response.Cookies["hqs"].Value =cookieValue;
Response.Cookies["hqs"].Expires = DateTime.Now.AddDays(1);

//用戶信息記入session
Session["userid"] = this.txt_user_id.Text.Trim();
Response.Redirect("Manage/index.aspx");
}
}
}

private bool checkCookie(string appValue)
{
bool isExist = false;

if (Request.Cookies["hqs"] != null)
{
string cookieValue = Request.Cookies["hqs"].Value;

char[] sp = new char[1]{'-'};
string appUserid = appValue.Split(sp)[0].ToString();
string appCookie = appValue.Split(sp)[1].ToString();

if (appUserid == this.txt_user_id.Text.Trim() appCookie != cookieValue)
isExist = true;
}
return isExist;
}

string sKey = username.Text.ToString().Trim(); // 得到Cache中的給定Key的值
string sUser = Convert.ToString(Cache[sKey]); // 檢查是否存在
if (sUser == null || sUser == String.Empty)
{

TimeSpan SessTimeOut = new TimeSpan(0, 0, System.Web.HttpContext.Current.Session.Timeout, 0, 0);//取得Session的過期時(shí)間
HttpContext.Current.Cache.Insert(sKey, sKey, null, DateTime.MaxValue, SessTimeOut, System.Web.Caching.CacheItemPriority.NotRemovable, null);//將值放入cache己方便單點(diǎn)登錄
//成功登錄
}
else if (Cache[sKey].ToString() == sKey)//如果這個(gè)賬號(hào)已經(jīng)登錄
{
ClientScript.RegisterStartupScript(GetType(), "提示", "script>alert('對(duì)不起,當(dāng)前用戶已經(jīng)登錄');/script>");
return;
}
else
{
Session.Abandon();//這段主要是為了避免不必要的錯(cuò)誤導(dǎo)致不能登錄
}