JDK8中对日期的处理（new）

        //1. LocalDate、LocalTime、LocalDateTime
        LocalDate localDate = LocalDate.now();
        System.out.println("localDate = " + localDate);// localDate = 2021-06-02
        LocalTime localTime = LocalTime.now();// localTime = 21:44:54.806
        System.out.println("localTime = " + localTime);
        LocalDateTime localDateTime = LocalDateTime.now();// localDateTime = 2021-06-02T21:44:54.806
        System.out.println("localDateTime = " + localDateTime);
        // 自定义时间
        LocalDate diyDate = LocalDate.of(2021, 12, 12);// diyDate = 2021-12-12
        System.out.println("diyDate = " + diyDate);
        //LocalDateTime diyLocalDateTime = LocalDateTime.of(LocalDate.of(2021, 6, 18), LocalTime.of(23, 23, 23));
        LocalDateTime diyLocalDateTime = LocalDateTime.of(localDate, localTime);// diyLocalDateTime = 2021-06-18T23:23:23
        System.out.println("diyLocalDateTime = " + diyLocalDateTime);
        // 时间的 ±
        LocalDate plus3Years = diyDate.plusYears(3);// plus3Years = 2024-12-12
        System.out.println("plus3Years = " + plus3Years);
        // 获取年月日，其中特别需要注意获取"月份"的差异
        int year = localDate.getYear();// year = 2021
        System.out.println("year = " + year);
        Month month = localDate.getMonth();
        System.out.println("localDate.getMonth() = " + month);// localDate.getMonth() = JUNE
        int monthValue = localDate.getMonthValue();// localDate.getMonthValue() = 6
        System.out.println("localDate.getMonthValue() = " + monthValue);
        //////////////////////////////////////////////
        //2. Instant : 时间戳。 （使用 Unix 元年  1970年1月1日 00:00:00 所经历的毫秒值）
        Instant now = Instant.now();
        System.out.println("now = " + now);
        //////////////////////////////////////////////
        // 3. 计算时间间隔
        // Duration : 用于计算两个“时间”间隔
        // Period : 用于计算两个“日期”间隔
        Period between = Period.between(diyDate, plus3Years);
        int years = between.getYears();
        System.out.println(diyDate + " 和 " + plus3Years + "之间的时间间隔(年)：" + years);// 3
        int months = between.getMonths();
        System.out.println(diyDate + " 和 " + plus3Years + "之间的时间间隔(年)：" + months);// 0，月份相同，所以为0。
        Instant now2 = Instant.now();
        System.out.println("now2 = " + now2);
        Duration duration = Duration.between(now, now2);
        long millis = duration.toMillis();
        System.out.println(now + " 和 " + now2 + " 的时间间隔(毫秒)：" + millis);
        //////////////////////////////////////////////
        //4. TemporalAdjuster、TemporalAdjusters：时间校正器
        LocalDate tempDate = localDate.of(2021, 6, 12);// tempDate = 2021-06-12
        System.out.println("tempDate = " + tempDate);
        // 经典问题1：获取当前日期所在的周一和周日。
        // 有可能今天就是周一
        if (tempDate.getDayOfWeek().equals(DayOfWeek.MONDAY)) {
            System.out.println(tempDate + " 是周一");
        } else {
            System.out.println(tempDate + " 不是周一");
            LocalDate previousMonday = tempDate.with(TemporalAdjusters.previous(DayOfWeek.MONDAY));
            System.out.println("本周周一是 " + previousMonday);// 2021-6-7
        }
        // 获取当前日期所在的周日
        if (tempDate.getDayOfWeek().equals(DayOfWeek.SUNDAY)) {
            System.out.println(tempDate + " 是周日");
        } else {
            System.out.println(tempDate + " 不是周日");
            LocalDate nextSunday = tempDate.with(TemporalAdjusters.next(DayOfWeek.SUNDAY));// nextSunday = 2021-06-13
            System.out.println("本周周日是 " + nextSunday);
        }
        // 经典问题2：获取本月第一天。
        LocalDate firstDayOfMonth = tempDate.with(TemporalAdjusters.firstDayOfMonth());// firstDayOfMonth = 2021-06-01
        System.out.println("firstDayOfMonth = " + firstDayOfMonth);
        //////////////////////////////////////////////
        // 5. 日期格式化 DateTimeFormatter
        DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        String formatDate = localDate.format(dateFormatter);// formatDate = 2021-06-02
        System.out.println("formatDate = " + formatDate);
        String formatDateTime = localDateTime.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));// formatDateTime = 2021-06-02 23:41:39
        System.out.println("formatDateTime = " + formatDateTime);
        LocalDate parseDate = LocalDate.parse("2021-02-11", dateFormatter);// parseDate = 2021-02-11
        System.out.println("parseDate = " + parseDate);
        LocalDateTime parseDateTime = LocalDateTime.parse("2021-06-02 23:48:06", dateTimeFormatter);// parseDateTime = 2021-06-02T23:48:06
        System.out.println("parseDateTime = " + parseDateTime);