Java 计算两日期区间的天数

输入时间是字符串类型：yyyy-MM-dd

public static void main(String[] args) {
    String startDate = "2021-09-09";
    String endDate = "2022-09-09";
    List everyday = getEveryday(startDate, endDate);
    System.out.println(everyday);
    System.out.println(everyday.size());
}

输出：

上代码：

    private static transient int gregorianCutoverYear = 1582;
    /** 闰年中每月天数 */
    private static final int[] DAYS_P_MONTH_LY= {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

    /** 非闰年中每月天数 */
    private static final int[] DAYS_P_MONTH_CY= {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

    public static final String SHORT_DATE_FORMAT = "yyyy-MM-dd";

    /** 代表数组里的年、月、日 */
    private static final int Y = 0, M = 1, D = 2;



    /**
     * 以循环的方式计算日期
     * @param beginDate endDate
     * @param
     * @return
     */
    public static List getEveryday(String beginDate , String endDate){
        if (StringUtils.isEmpty(endDate)){
            SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
            Date date = new Date();
            endDate = simpleDateFormat.format(date);
        }
        long days = countDay(beginDate, endDate);
        int[] ymd = splitYMD( beginDate );
        List everyDays = new ArrayList();
        everyDays.add(beginDate);
        for(int i = 0; i < days; i++){
            ymd = addOneDay(ymd[Y], ymd[M], ymd[D]);
            everyDays.add(formatYear(ymd[Y])+"-"+formatMonthDay(ymd[M])+"-"+formatMonthDay(ymd[D]));
        }
        return everyDays;
    }
    /**
     * 计算两个日期之间相隔的天数
     * @param begin
     * @param end
     * @return
     * @throws ParseException
     */
    public static long countDay(String begin,String end){
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
        Date beginDate , endDate;
        long day = 0;
        try {
            beginDate= format.parse(begin);
            endDate= format.parse(end);
            day=(endDate.getTime()-beginDate.getTime())/(24*60*60*1000);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return day;
    }

    /**
     * 将代表日期的字符串分割为代表年月日的整形数组
     * @param date
     * @return
     */
    public static int[] splitYMD(String date){
        date = date.replace("-", "");
        int[] ymd = {0, 0, 0};
        ymd[Y] = Integer.parseInt(date.substring(0, 4));
        ymd[M] = Integer.parseInt(date.substring(4, 6));
        ymd[D] = Integer.parseInt(date.substring(6, 8));
        return ymd;
    }


    /**
     * 日期加1天
     * @param year
     * @param month
     * @param day
     * @return
     */
    private static int[] addOneDay(int year, int month, int day){
        if(isLeapYear( year )){
            day++;
            if( day > DAYS_P_MONTH_LY[month -1 ] ){
                month++;
                if(month > 12){
                    year++;
                    month = 1;
                }
                day = 1;
            }
        }else{
            day++;
            if( day > DAYS_P_MONTH_CY[month -1 ] ){
                month++;
                if(month > 12){
                    year++;
                    month = 1;
                }
                day = 1;
            }
        }
        int[] ymd = {year, month, day};
        return ymd;
    }


    /**
     * 检查传入的参数代表的年份是否为闰年
     * @param year
     * @return
     */
    public static boolean isLeapYear(int year) {
        return year >= gregorianCutoverYear ?
                ((year%4 == 0) && ((year%100 != 0) || (year%400 == 0))) : (year%4 == 0);
    }

    /**
     * 将不足四位的年份补足为四位
     * @param decimal
     * @return
     */
    public static String formatYear(int decimal){
        DecimalFormat df = new DecimalFormat("0000");
        return df.format( decimal );
    }

    /**
     * 将不足两位的月份或日期补足为两位
     * @param decimal
     * @return
     */
    public static String formatMonthDay(int decimal){
        DecimalFormat df = new DecimalFormat("00");
        return df.format( decimal );
    }