clearing two dimensional session array using jsp
===

i have a two dimensional session array and i'm trying to clear it after the bill is printed. to do so i'm using this code

    <script type="text/javascript">
        function textsizer(e) {
        var evtobj=window.event? event : e;
        var element = evtobj.target ? evtobj.target : evtobj.srcElement;
        if (element.tagName.toLowerCase() == "body") {
            var unicode=evtobj.charCode? evtobj.charCode : evtobj.keyCode;
            var actualkey=String.fromCharCode(unicode)
            if(actualkey=="x"){
    			show_confirm()
    			function show_confirm(){
    			var con = confirm("Are You Sure you wan to cancel this bill?");
    			if (con ==true){
                	session.invalidate();
    			}
    			else{
      			alert("You pressed Cancel!");
      			}
    			}
            }
        }
    }
    document.onkeypress=textsizer
    </script>

 but this code is not clearing the session. i tried it using google chrome and internet explorer but didn't work. can anyone help me on this thing?
i also tried to do it with php but it also didn't work for me. my case i want to delete session by pressing x on key board  there is no matter what is the language, i just want to clear the session pressing x key 