java天数计算函数(当前月天数、某月总天数及某月剩余天数)4种方法实现代码

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

    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);
    }

 
    /**
     * 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);
    }

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

 
    /**
     * 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);
    }

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

    public static void main(String[] args) throws ParseException {
        Date currentTime = new Date();
        SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String dateString = formatter.format(currentTime);
        System.out.println(dateString);
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy年MM月dd日HH时mm分ss秒");
        String dateString2 = dateFormat.format(currentTime);
        System.out.println(dateString2);
        Date date1 = dateFormat.parse(dateString2);
        String dateString3 = formatter.format(date1);
        System.out.println(dateString3);
        // 将日期字符串转换为LocalDate对象
        LocalDate date = LocalDate.parse("2023-04-06");
        // 将LocalDate对象格式化为指定格式的字符串
        DateTimeFormatter formatter1 = DateTimeFormatter.ofPattern("yyyy年M月d日");
        String formattedDate = date.format(formatter1);
        System.out.println(formattedDate);
        // 将格式化后的字符串转换为LocalDate对象
        LocalDate parsedDate = LocalDate.parse(formattedDate, formatter1);
        // 将LocalDate对象转换为指定格式的字符串
        String parsedDateString = parsedDate.format(DateTimeFormatter.ofPattern("yyyy-MM-dd"));
        System.out.println(parsedDateString);
        // 确认两个日期字符串相等
        assert parsedDateString.equals("2023-04-06");
        // 确认两个LocalDate对象相等
        assert parsedDate.equals(date);
        System.out.println("---------------------");
        String sdate="2023-04-06";
        String sdate2="2023年4月6日";
        String sdate3="2023-04";
        String sdate4="2023年4月";
        System.out.println(convertDateToChs(sdate));
        System.out.println(convertToChinese(sdate));
        System.out.println((convertDateToEn(sdate2)));
        System.out.println((convertDateToEnglish(sdate2)));
        System.out.println((convertToShortChinese(sdate3)));
        System.out.println((convertToShortEnglish(sdate4)));
        String dateStr = "2023-02";
        int days = getDaysByDate(dateStr);
        System.out.println(dateStr + " has " + days + " days.");
        System.out.println("今年有" +   getDaysInCurrentYear() + " days.");
        System.out.println("今年已过去" +   getDaysPassedInCurrentYear() + " days.");
        System.out.println("今年剩余" +   getDaysEndInCurrentYear() + " days.");
    }