private Calendar getStartOfDate(Date date) {
        Calendar calendar = Calendar.getInstance();
        calendar.clear();
        calendar.setTime(date);
        calendar.set(Calendar.HOUR_OF_DAY, 0);
        calendar.set(Calendar.MINUTE, 0);
        calendar.set(Calendar.SECOND, 0);
        calendar.set(Calendar.MILLISECOND, 0);
        return calendar;
    }