Java将时间按月份分段的实现思路与方法

Calendar calendar = Calendar.getInstance();

Date time = new Date;
calendar.setTime(time);

calendar.set(Calendar.YEAR, 2021); // 年
calendar.add(Calendar.MONTH, 1); // 月
calendar.set(Calendar.DAY_OF_MONTH, 1); // 日

public static List<Long> getIntervalTimeByMonth(Date startTime, Date endTime) {
    List<Long> dateList = new ArrayList<>();
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(startTime);
    dateList.add(calendar.getTimeInMillis());
    while (calendar.getTimeInMillis() < endTime.getTime()) {
        // 当月底
        calendar.add(Calendar.MONTH, 1);
        calendar.set(Calendar.DAY_OF_MONTH, 1);
        calendar.add(Calendar.DATE, -1);
        calendar.set(Calendar.HOUR_OF_DAY, 23);
        calendar.set(Calendar.MINUTE, 59);
        calendar.set(Calendar.SECOND, 59);
        if(calendar.getTimeInMillis() >= endTime.getTime()){
            dateList.add(endTime.getTime());
            break;
        }
        // 下月初
        calendar.add(Calendar.DATE, 1);
        calendar.set(Calendar.HOUR_OF_DAY, 0);
        calendar.set(Calendar.MINUTE, 0);
        calendar.set(Calendar.SECOND, 0);
        dateList.add(calendar.getTimeInMillis());
    }
    return dateList;
}

public static void main(String[] args) throws ParseException {
    SimpleDateFORMat sdf1 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    Date beginDate = sdf.parse("2020-07-15");
    Date endDate = sdf.parse("2021-07-05");
    List<Long> endDateList = DateUtil.getIntervalTimeByMonth(beginDate, endDate);
    for (int i = 0; i < endDateList.size(); i++) {
        Long beginStr = endDateList.get(i);
        String begin1 = sdf1.format(new Date(beginStr));
        System.out.println("第" + i + "段时间区间:" + begin1);
    }
}