Java Calendar 多用，日期 加减

服务需要订购一个月，订购一个月 不等于增加 30天；若是1,3,5的话应该 31天，要善用 

Calendar

    public static void main(String[] args) throws ParseException {
        String dateStr = "2023-05-01 09:00:00";

        DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date date = dateFormat.parse(dateStr);


        Calendar calendar1 = Calendar.getInstance();
        Calendar calendar2 = Calendar.getInstance();
        calendar1.setTime(date);
        calendar2.setTime(date);


        calendar1.add(Calendar.MONTH, 1); //加一个月
        calendar2.add(Calendar.DATE, 30); //加30天

        System.out.println(dateFormat.format(calendar1.getTime()));
        System.out.println(dateFormat.format(calendar2.getTime()));
    }