java - how to send an alert when session expires -

i wanted throw alert when session expires , when press ok button in alert box take login page. thought create timer , timertask , in run method of later class check if session exists or not. tried create class in jsp page showing error. can create in servlet pages in jsp , idea not useful.now created sessionlistner , in session destroyed method want link login page have problem here too.i can not use response method in sessiondestroyed method.please tell me there other ways

you can use javascript like:

        var sessiontimeout = "<%= session.timeout %>";         function displaysessiontimeout()         {             //assigning minutes left session timeout label             document.getelementbyid("<%= lblsessiontime.clientid %>").innertext =                                                                          sessiontimeout;             sessiontimeout = sessiontimeout - 1;              //if session not less 0             if (sessiontimeout >= 0)                 //call function again after 1 minute delay                 window.settimeout("displaysessiontimeout()", 60000);             else             {                 //show message box                 alert("your current session over.");             }         } 

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