a.html~

    <html><head>  
    <script>  
    <!--  
    <%  
    String clock = request.getParameter( "clock" );  
    if( clock == null ) clock = "180";  
    %>  
    var timeout = 5;  
    function timer()  
    {  
    if( --timeout > 0 )  
    {  
    document.forma.clock.value = timeout;  
    window.setTimeout( "timer()", 1000 );  
    }  
    else  
    {  
    document.forma.clock.value = "Time over";  
    ///disable submit-button etc  
    }  
    }  
    //-->  
    </script>  
    <body>  
    <form action="<%=request.getRequestURL()%>" name="forma">  
    Seconds remaining: <input type="text" name="clock" value="<%=clock%>" style="border:0px solid white">  
    ...  
    </form>  
    <script>  
    <!--  
    timer();  
    //-->  
    </script>  
    </body></html>  