计算考试剩余时间

        String start = (String) session.getAttribute("StartTime");
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date date = null;
        try {
            date = format.parse(start);
        } catch (ParseException e) {
            throw new ServletException(e);
        }

        Calendar c = Calendar.getInstance();

        long escape = (c.getTimeInMillis() - date.getTime()) / (1000 * 60);
        long remain = (Integer) session.getAttribute("Minutes") - escape;