如何防范同一帐户重复登录系统

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如何防止控制客户端使其用同一帐户重复登录系统.

解决思路：

维护一online表，查看有登陆，就不允许再次登陆，以sessionid作为唯一标识符号，也可以产生一个ＧＵＩＤ发到ＣＯＯＫＩＥ中，以区分不同的ＣＬＩＥＮＴ，再佐以ＪＳ，可以达到更好的效果，比如离开后自动离线

解决代码：

public virtual void Application_Start(object sender, EventArgs e)
??{
???// reset the mailer indicator
???Application["MailerStatus"] = "All Mailings Complete";

???// initialize a datatable for users online
???DataTable objUserTable = new DataTable();
objUserTable.Columns.Add("SessionID",System.Type.GetType("System.Guid"));
objUserTable.Columns.Add("PeopleID",System.Type.GetType("System.Int32"));
objUserTable.Columns.Add("ShowDetail",System.Type.GetType("System.Boolean"));
???DataColumn[] pk = new DataColumn[1];
???pk[0] = objUserTable.Columns[0];
???objUserTable.PrimaryKey = pk;
???Application["UserTable"] = objUserTable;
??}
?
??///
??/// The Session_Start event adds user session information to
??/// Application["UserTable"].
??///
??public virtual void Session_Start(object sender, EventArgs e)
??{
???Application.Lock();
???//Application.Lock ();
?DataTable objUserTable = (DataTable)Application["UserTable"];
???DataRow objRow = objUserTable.NewRow();
???Guid objGuid = Guid.NewGuid();
???objRow[0] = objGuid;
???Session["PfSessionID"] = objRow[0];
???objRow[1] = 0;
???objRow[2] = false;
???objUserTable.Rows.Add(objRow);
???Application["UserTable"] = objUserTable;
???Application.UnLock();
??}

?
??///
?/// The Session_End event deletes user session information from
??/// Application["UserTable"].
??///
??public virtual void Session_End(object sender, EventArgs e)
??{
???Application.Lock();
??DataTable objUserTable = (DataTable)Application["UserTable"];
??objUserTable.Rows.Find((Guid)Session["PfSessionID"]).Delete();
???Application["UserTable"] = objUserTable;
???Application.UnLock();
??}

……