java天数计算函数(当前月天数、某月总天数、某月剩余天数)4种方法实现

1,Java8 LocalDate

    public static int getDaysOfMonth(String dateStr) {
        LocalDate date = LocalDate.parse(dateStr + "-01");
        return date.lengthOfMonth();
    }

2,利用日历函数

    public static int getDaysOfMonth(String dateStr) throws ParseException {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM");
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(sdf.parse(dateStr));
        return calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
    }

3,也是利用日历函数，但是不需要 throws ParseException

    /**
     * 获取日期当月的天数
     * @param dateStr yyyy-MM 或者yyyy-MM-dd
     * */
    public static int getDaysByDate(String dateStr){
        int year= Integer.parseInt(dateStr.substring(0,4));
        int month=Integer.parseInt(dateStr.substring(5,7));
        Calendar c = Calendar.getInstance();
        c.set(year, month, 0);
        return c.get(Calendar.DAY_OF_MONTH);
    }

测试样例代码： 

        String dateStr = "2023-01";
        int days = getDaysOfMonth(dateStr);
        System.out.println(dateStr + " has " + days + " days.");

4,当月剩余天数

 
    /**
     * 当月剩余天数
     * @param date 格式yyyy-MM-dd
     * */
    public static Integer monthEndNum(String date){
        SimpleDateFormat format=new SimpleDateFormat("yyyy-MM-dd");
        Date dateTime = null;
        try {
            dateTime = format.parse(date);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        Calendar c = Calendar.getInstance();
        c.setTime(dateTime);
        int today = c.get(Calendar.DAY_OF_MONTH);
        int last = c.getActualMaximum(Calendar.DAY_OF_MONTH);
        return last - today;
    }
 
  public static void main(String[] args) {
        Integer days = monthEndNum("2023-01-20");
        System.out.println("2023年1月剩余天数:"+days);
    }

5，获取当前月天数

    //获取当前月的天数
    public static int getDaysOfCurrentMonth() {
        Calendar calendar = Calendar.getInstance();
        return calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
    }