在报表需求中，经常需要按日、周、月分组，但是如果某段时间没有对应的记录，时间轴会不连续

我们可以使用JAVA的Calendar来预设某段时间的时间轴

传入时间区间，获取轴
直接上 代码。

public class DateUtil {
    
	// 当然入参也可以换成localdate、date等类型，出参也可以换成月-日等

    private static final DateTimeFormatter format = DateTimeFormatter.ofPattern("MM/dd");
    
	 /**
     * 获取day1到day2的周间隔
     * @return
     */
    public static List<String> getWeekSection(LocalDateTime day1, LocalDateTime day2) {
    
        List<String> list = new ArrayList<>();

        Calendar start = Calendar.getInstance();
        start.setMinimalDaysInFirstWeek(4);//设置一年第一周归属
        start.setTime(Date.from(day1.atZone(ZoneId.systemDefault()).toInstant()));
        start.setFirstDayOfWeek(Calendar.MONDAY);
        start.set(Calendar.DAY_OF_WEEK, start.getFirstDayOfWeek());

        Calendar end = Calendar.getInstance();
        end.setMinimalDaysInFirstWeek(4);//设置一年第一周归属
        end.setTime(Date.from(day2.atZone(ZoneId.systemDefault()).toInstant()));
        end.setFirstDayOfWeek(Calendar.MONDAY);
        end.set(Calendar.DAY_OF_WEEK, end.getFirstDayOfWeek() + 6);

        while (!start.after(end)){
    
            //该年该周
            String yearWeek = start.get(Calendar.YEAR)+"/"+start.get(Calendar.WEEK_OF_YEAR);
            //该周开始日期
            LocalDateTime sectionStart = LocalDateTime.ofInstant(start.getTime().toInstant(), ZoneId.systemDefault());
            //该周结束日期
            start.add(Calendar.DAY_OF_MONTH, 6);
            LocalDateTime sectionEnd = LocalDateTime.ofInstant(start.getTime().toInstant(), ZoneId.systemDefault());

            list.add(yearWeek);
            //下一周
            start.add(Calendar.DAY_OF_MONTH, 1);
        }
        return list;
    }

    /**
     * 获取day1到day2的间隔7天周期
     * @return
     */
    public static List<String> getWeekSection2(LocalDateTime day1, LocalDateTime day2) {
    
        List<String> list = new ArrayList<>();

        Calendar start = Calendar.getInstance();
        start.setMinimalDaysInFirstWeek(4);//设置一年第一周归属
        start.setTime(Date.from(day1.atZone(ZoneId.systemDefault()).toInstant()));
        start.setFirstDayOfWeek(Calendar.MONDAY);
        start.set(Calendar.DAY_OF_WEEK, start.getFirstDayOfWeek());

        Calendar end = Calendar.getInstance();
        end.setMinimalDaysInFirstWeek(4);//设置一年第一周归属
        end.setTime(Date.from(day2.atZone(ZoneId.systemDefault()).toInstant()));
        end.setFirstDayOfWeek(Calendar.MONDAY);
        end.set(Calendar.DAY_OF_WEEK, end.getFirstDayOfWeek() + 6);

        while (!start.after(end)){
    
            //该周开始日期
            LocalDateTime sectionStart = LocalDateTime.ofInstant(start.getTime().toInstant(), ZoneId.systemDefault());
            //该周结束日期
            start.add(Calendar.DAY_OF_MONTH, 6);
            LocalDateTime sectionEnd = LocalDateTime.ofInstant(start.getTime().toInstant(), ZoneId.systemDefault());
            String startStr = format.format(sectionStart);
            //设置出参
            String endStr = format.format(sectionEnd);
            list.add(startStr+"-"+endStr);
            //下一周
            start.add(Calendar.DAY_OF_MONTH, 1);
        }
        return list;
    }


    /**
     * 获取day1到day2的间隔
     * @return
     */
    public static List<String> getDaySection(LocalDateTime day1, LocalDateTime day2) {
    
        //出参
        List<String> list = new ArrayList<>();

        //localDateTime转date
        ZoneId zone = ZoneId.systemDefault();
        Instant instant1 = day1.atZone(zone).toInstant();
        Date date1 = Date.from(instant1);

        Instant instant2 = day2.atZone(zone).toInstant();
        Date date2 = Date.from(instant2);

        Calendar start = Calendar.getInstance();
        start.setTime(date1);

        Calendar end = Calendar.getInstance();
        end.setTime(date2);

        while (!start.after(end)){
    
            String year = start.get(Calendar.YEAR) + "";
            String month = (((start.get(Calendar.MONTH) + 1) < 10 ?"0":"") + (start.get(Calendar.MONTH) + 1));
            String day = ((start.get(Calendar.DATE) < 10 ?"0":"") + start.get(Calendar.DATE));
            list.add(year + "/" + month + "/" + day);
            start.add(Calendar.DATE,1);
        }

        return list;
    }

    /**
     * 获取day1到day2的月间隔
     * @return
     */
    public static List<String> getMonthSection(LocalDateTime day1, LocalDateTime day2) {
    
        //出参
        List<String> list = new ArrayList<>();

        //localDateTime转date
        ZoneId zone = ZoneId.systemDefault();
        Instant instant1 = day1.atZone(zone).toInstant();
        Date date1 = Date.from(instant1);

        Instant instant2 = day2.atZone(zone).toInstant();
        Date date2 = Date.from(instant2);

        Calendar start = Calendar.getInstance();
        start.setTime(date1);

        Calendar end = Calendar.getInstance();
        end.setTime(date2);

        while (!start.after(end)){
    
            String month = (((start.get(Calendar.MONTH) + 1) < 10 ?"0":"") + (start.get(Calendar.MONTH) + 1));
            String time = start.get(Calendar.YEAR) + "/" + month;
            list.add(time);
            start.add(Calendar.MONTH,1);
        }

        return list;
    }

    public static void main(String[] args) {
    
//测试一下

//        DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
//        LocalDateTime ldt = LocalDateTime.parse("2021-02-12 00:00:00",df);
//        System.out.println(getDaySection(ldt,LocalDateTime.now()));

//        DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
//        LocalDateTime ldt = LocalDateTime.parse("2021-02-12 00:00:00",df);
//        System.out.println(getMonthSection(ldt,LocalDateTime.now()));
//
        DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        LocalDateTime ldt1 = LocalDateTime.parse("2021-12-20 00:00:00",df);
        LocalDateTime ldt2 = LocalDateTime.parse("2022-01-30 23:59:59",df);
        System.out.println(getWeekSection(ldt1,ldt2));

    }

}