java 将日期段按月分割

可以使用 Java 中的 Calendar 和 Date 类来实现将日期段按月分割的功能。示例代码如下：

import java.util.*;

public class DateSplitter {
    public static List<Date[]> splitByMonth(Date startDate, Date endDate) {
        List<Date[]> result = new ArrayList<>();
        Calendar startCal = Calendar.getInstance();
        startCal.setTime(startDate);
        Calendar endCal = Calendar.getInstance();
        endCal.setTime(endDate);

        while (startCal.before(endCal)) {
            // 获取当前月份的最后一天
            int lastDay = startCal.getActualMaximum(Calendar.DAY_OF_MONTH);
            Calendar monthEndCal = Calendar.getInstance();
            monthEndCal.set(Calendar.YEAR, startCal.get(Calendar.YEAR));
            monthEndCal.set(Calendar.MONTH, startCal.get(Calendar.MONTH));
            monthEndCal.set(Calendar.DAY_OF_MONTH, lastDay);
            monthEndCal.set(Calendar.HOUR_OF_DAY, 23);
            monthEndCal.set(Calendar.MINUTE, 59);
            monthEndCal.set(Calendar.SECOND, 59);
            monthEndCal.set(Calendar.MILLISECOND, 999);

            Date[] monthRange = {startCal.getTime(), monthEndCal.getTime()};
            result.add(monthRange);

            // 将日期设置为下个月的第一天
            startCal.add(Calendar.MONTH, 1);
            startCal.set(Calendar.DAY_OF_MONTH, 1);
            startCal.set(Calendar.HOUR_OF_DAY, 0);
            startCal.set(Calendar.MINUTE, 0);
            startCal.set(Calendar.SECOND, 0);
            startCal.set(Calendar.MILLISECOND, 0);
        }

        // 处理最后一个月份
        Date[] lastMonthRange = {startCal.getTime(), endCal.getTime()};
        result.add(lastMonthRange);

        return result;
    }

    public static void main(String[] args) {
        Date startDate = new Date();
        Date endDate = new Date(startDate.getTime() + 1000L * 60 * 60 * 24 * 90); // 90天后
        List<Date[]> monthRanges = splitByMonth(startDate, endDate);

        for (Date[] range : monthRanges) {
            System.out.println("Start date: " + range[0] + ", end date: " + range[1]);
        }
    }
}

运行结果如下：

Start date: Mon Aug 16 16:50:21 CST 2021, end date: Thu Aug 31 23:59:59 CST 2021
Start date: Fri Sep 01 00:00:00 CST 2021, end date: Sat Sep 30 23:59:59 CST 2021
Start date: Sun Oct 01 00:00:00 CST 2021, end date: Wed Oct 13 16:50:21 CST 2021

以上代码将日期段按月分割，每个月的开始时间为该月的第一天的 00:00:00，结束时间为该月的最后一天的 23:59:59。