java用LocalDateTime类获取当天时间、前一天时间及本周/本月的开始和结束时间

        // 获取当天日期
        LocalDate now = LocalDate.now();
        // 当天开始时间
        LocalDateTime todayStart = now.atStartOfDay();
        // 当天结束时间
        LocalDateTime todayEnd = LocalDateTime.of(now, LocalTime.MAX);
        // 周一
        LocalDate monday = now.with(TemporalAdjusters.previousOrSame(DayOfWeek.MONDAY));
        // 周日
        LocalDate sunday = now.with(TemporalAdjusters.nextOrSame(DayOfWeek.SUNDAY));
        // 本周开始时间
        LocalDateTime weekStart = monday.atStartOfDay();
        // 本周结束时间
        LocalDateTime weekEnd = LocalDateTime.of(sunday, LocalTime.MAX);
        // 本月1号
        LocalDate firstDayOfMonth = now.with(TemporalAdjusters.firstDayOfMonth());
        // 本月最后一天
        LocalDate lastDayOfMonth = now.with(TemporalAdjusters.lastDayOfMonth());
        // 本月1号的开始时间
        LocalDateTime firstDayOfMonthStart = firstDayOfMonth.atStartOfDay();
        // 本月最后一天的最后时间
        LocalDateTime firstDayOfMonthEnd = LocalDateTime.of(lastDayOfMonth, LocalTime.MAX);
        // 今年第一天
        LocalDate beginTime = LocalDate.now().with(TemporalAdjusters.firstDayOfYear());
        // 今年最后一天
        LocalDate endTiime = LocalDate.now().with(TemporalAdjusters.lastDayOfYear());
        //获取前一天日期
        LocalDate yesterday2 = LocalDate.now().minusDays(1);
        DateTimeFormatter pattern = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        System.out.println("当天开始时间 = " + todayStart.format(pattern) + "  时间戳 ：" + todayStart.toInstant(ZoneOffset.of("+8")).toEpochMilli());
        System.out.println("当天结束时间 = " + todayEnd.format(pattern) + "  时间戳 ：" + todayEnd.toInstant(ZoneOffset.of("+8")).toEpochMilli());
        System.out.println("本周开始时间 = " + weekStart.format(pattern) + "  时间戳 ：" + weekStart.toInstant(ZoneOffset.of("+8")).toEpochMilli());
        System.out.println("本周结束时间 = " + weekEnd.format(pattern) + "  时间戳 ：" + weekEnd.toInstant(ZoneOffset.of("+8")).toEpochMilli());
        System.out.println("本月开始时间 = " + firstDayOfMonthStart.format(pattern) + "  时间戳 ：" + firstDayOfMonthStart.toInstant(ZoneOffset.of("+8")).toEpochMilli());
        System.out.println("本月结束时间 = " + firstDayOfMonthEnd.format(pattern) + "  时间戳 ：" + firstDayOfMonthEnd.toInstant(ZoneOffset.of("+8")).toEpochMilli());

LocalDate.now().minusYears(x);  //当前日期减去指定的年份
​​​​​​​LocalDate.now().minusMonths(x); //当前日期减去指定的月份
LocalDate.now().minusDays(x);   //当前日期减去指定的天数 
LocalDate.now().minusWeeks(x);  //当前日期减去指定的周数 

DateTimeFormatter formatter3 = DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss");
//格式化
String str4 = formatter3.format(LocalDateTime.now());
System.out.println(str4);//2021-09-22 06:33:08
//解析
TemporalAccessor parse1 = formatter3.parse(str4);
System.out.println(parse1);//{NanoOfSecond=0, MilliOfSecond=0, MinuteOfHour=34, HourOfAmPm=6, SecondOfMinute=6, MicroOfSecond=0},ISO resolved to 2021-09-22
//解析
String dateString = "2023-07-13 15:30:00";
LocalDateTime dateTime = LocalDateTime.parse(dateString, formatter3);

DateTimeFormatter formatter3 = DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss");

LocalDateTime start = LocalDateTime.of(2023, 6, 1, 0, 0, 0);
LocalDateTime end = LocalDateTime.of(2023, 6, 28, 0, 0, 0);
Duration duration = Duration.between(start, end);
long days = duration.toDays();
System.out.println(days); // 输出：27