计算日期偏移量函数

protected Date adustOffSetDate(Date useDate, int BEGIN_DATE_OFFSET) {

        if(useDate == null){
            return null;
        }
        
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(useDate);

        int volatilityNum = BEGIN_DATE_OFFSET >= 0 ? 1 : -1;

        for (int i = 0; i < Math.abs(BEGIN_DATE_OFFSET); i++) {

            calendar.add(Calendar.DATE, volatilityNum);
            int dayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);

            if (Calendar.SATURDAY == dayOfWeek || Calendar.SUNDAY == dayOfWeek) {
                i--;
            }
        }

        return calendar.getTime();

    }