I need to call an action on load of a JSP. To keep track of number of users who visited that page.

I hav an action VisitorCounterAction. Where il update the database. On load of the JSP im calling an ajax function callCounter();

{

        alert("callCounter");
        if (window.XMLHttpRequest)
        {// code for IE7+, Firefox, Chrome, Opera, Safari
        xmlhttp=new XMLHttpRequest();
        }
        else
        {// code for IE6, IE5
        xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
        }

        // i need some correction here
        xmlhttp.open("GET",VisitorCounterAction,false);
        xmlhttp.send(null);
        alert("callCounter returned from Action");
        }

I am getting an exception as:

/web/guest/content?p_p_id=31&p_p_lifecycle=0&p_p_state=pop_up&p_p_mode=view&_31_struts_action=%2Fimage_gallery%2Fview_slide_show&_31_folderId=10605 generates exception: null

Please help me with this. Or any other way to call the Action. I can't reload the page as it'll call onload function again.

Thanks, Dj