Java8常用日期时间方法

常用日期时间方法

1. 使用plus方法获取n天/月/年后的时间

使用plus方法可以计算n小时/天/月/年后的时间。根据API的不同，所支持的单位也不同。

    /**
     * 使用plus方法获取n天/月/年后的时间
     */
    public static void plusUsage() {
        LocalDate nowLocalDate = LocalDate.now();
        System.out.println("nowLocalDate: " + nowLocalDate);

        LocalDate nowLocalDatePlus1Day = nowLocalDate.plusDays(1);
        System.out.println("nowLocalDatePlus1Day: " + nowLocalDatePlus1Day);

        LocalDate nowLocalDatePlus1Month = nowLocalDate.plusMonths(1);
        System.out.println("nowLocalDatePlus1Month: " + nowLocalDatePlus1Month);

        LocalDate nowLocalDatePlus1Year = nowLocalDate.plusYears(1);
        System.out.println("nowLocalDatePlus1Year: " + nowLocalDatePlus1Year);

        // 指定单位
        LocalDate nowLocalDatePlus1Day2 = nowLocalDate.plus(1, ChronoUnit.DAYS);
        System.out.println("nowLocalDatePlus1Day2: " + nowLocalDatePlus1Day2);

        // 使用ZonedDateTime获取时间戳及时间计算
        ZonedDateTime nowZonedDateTime = ZonedDateTime.now();
        System.out.println("nowZonedDateTime: " + nowZonedDateTime
                + ", epochMilli: " + nowZonedDateTime.toInstant().toEpochMilli());

        // 获取1年后的时间戳（常用于设置有效期）
        ZonedDateTime nowZonedDateTimePlus1Year = nowZonedDateTime.plus(1, ChronoUnit.YEARS);
        System.out.println("nowZonedDateTimePlus1Year: " + nowZonedDateTimePlus1Year
                + ", epochMilli: " + nowZonedDateTimePlus1Year.toInstant().toEpochMilli());

    }

打印记录为：

nowLocalDate: 2022-08-21
nowLocalDatePlus1Day: 2022-08-22
nowLocalDatePlus1Month: 2022-09-21
nowLocalDatePlus1Year: 2023-08-21
nowLocalDatePlus1Day2: 2022-08-22
nowZonedDateTime: 2022-08-21T22:16:50.011+08:00[Asia/Shanghai], epochMilli: 1661091410011
nowZonedDateTimePlus1Year: 2023-08-21T22:16:50.011+08:00[Asia/Shanghai], epochMilli: 1692627410011

LocalDate仅表示日期，所以不支持Hours等操作。同样，LocalTime仅表示时间，则不支持Day等操作。

与plus操作相对应，minus表示减去对应的单位。

常用API及支持的单位：

类名	API描述	plus支持的单位
LocalDate	本地日期	DAYS WEEKS MONTHS YEARS DECADES CENTURIES MILLENNIA
LocalTime	本地时间	NANOS MICROS MILLIS SECONDS MINUTES HOURS HALF_DAYS
LocalDateTime	本地日期时间	LocalDate和LocalTime的合集
Instant	时间戳	NANOS MICROS MILLIS SECONDS MINUTES HOURS HALF_DAYS DAYS
ZonedDateTime	带时区的日期时间	LocalDate和LocalTime的合集
OffsetDateTime	带偏移量的日期时间	LocalDate和LocalTime的合集

2. 常见日期时间计算

使用java.time.temporal.Temporal#with(java.time.temporal.TemporalAdjuster) 可以计算最大最小等日期计算。

TemporalAdjusters 常用函数

函数名	描述
dayOfWeekInMonth(int ordinal,DayOfWeek dayOfWeek)	获取当前月的第几个星期几
firstDayOfMonth()	当前月的第一天
firstDayOfNextMonth()	下个月的第一天
firstDayOfYear()	当前年的第一天
firstDayOfNextYear()	第二年的第一天
firstInMonth(DayOfWeek dayOfWeek)	当前月的第一个星期几
lastDayOfMonth()	当前月的最后一天
lastDayOfYear()	当前年的最后一天
lastInMonth(DayOfWeek dayOfWeek)	当前月的最后一个星期几
next(DayOfWeek dayOfWeek)	下一个星期几(可以跨月或者年)
nextOrSame(DayOfWeek dayOfWeek)	下一个或者相同的星期几(如果和当前相同)
previous(DayOfWeek dayOfWeek)	上一个星期几
previousOrSame(DayOfWeek dayOfWeek)	上一个或者相同的星期几
ofDateAdjuster(UnaryOperator dateBasedAdjuster)	自定义

参考文档：

https://docs.oracle.com/javase/8/docs/api/java/time/temporal/TemporalAdjusters.html

eg.

    /**
     * localDate with 常见用法
     */
    public static void localDataWithUsage() {
        // 当前时间 2023-02-05
        LocalDate nowLocalDate = LocalDate.now();
        // dayOfWeekInMonth 表示同一个月的第几个星期几
        // 比如 第三个星期日 2023-02-19
        LocalDate thirdSundayOfMonth = nowLocalDate.with(TemporalAdjusters.dayOfWeekInMonth(3, DayOfWeek.SUNDAY));
        // 当前月的第一天 2023-02-01
        LocalDate firstDayOfMonth = nowLocalDate.with(TemporalAdjusters.firstDayOfMonth());
        // 下个月的第一天 2023-03-01
        LocalDate firstDayOfNextMonth = nowLocalDate.with(TemporalAdjusters.firstDayOfNextMonth());
        // 当前年的第一天 2023-01-01
        LocalDate firstDayOfYear = nowLocalDate.with(TemporalAdjusters.firstDayOfYear());
        // 第二年的第一天 2024-01-01
        LocalDate firstDayOfNextYear = nowLocalDate.with(TemporalAdjusters.firstDayOfNextYear());
        // firstInMonth 当前月的第一个星期几 即 dayOfWeekInMonth(1, DayOfWeek)
        // 第一个星期日 2023-02-05
        LocalDate firstSundayOfMonth = nowLocalDate.with(TemporalAdjusters.firstInMonth(DayOfWeek.SUNDAY));
        // 当前月的最后一天 2023-02-28
        LocalDate lastDayOfMonth = nowLocalDate.with(TemporalAdjusters.lastDayOfMonth());
        // 当前年的最后一天 2023-12-31
        LocalDate lastDayOfYear = nowLocalDate.with(TemporalAdjusters.lastDayOfYear());
        // lastInMonth 当前月的最后一个星期几
        // 最后一个星期日 2023-02-26
        LocalDate lastSundayOfMonth = nowLocalDate.with(TemporalAdjusters.lastInMonth(DayOfWeek.SUNDAY));
        // 下一个星期几 (可以跨月或者年)
        // 下一个星期日 2023-02-12
        LocalDate nextSunday = nowLocalDate.with(TemporalAdjusters.next(DayOfWeek.SUNDAY));

        // 下一个或者相同的星期几(如果和当前相同)
        // 当前是 2023-02-05 星期日 则 nextOfSameSunday 为 2023-02-05
        LocalDate nextOfSameSunday = nowLocalDate.with(TemporalAdjusters.nextOrSame(DayOfWeek.SUNDAY));

        // 当前是 2023-02-05 星期日 则 nextOfSameMonday 为 2023-02-06
        LocalDate nextOfSameMonday = nowLocalDate.with(TemporalAdjusters.nextOrSame(DayOfWeek.MONDAY));

        // 上一个星期日 2023-01-29
        LocalDate previousSunday = nowLocalDate.with(TemporalAdjusters.previous(DayOfWeek.SUNDAY));
        // 上一个或者相同的星期日 2023-02-05
        LocalDate previousOrSameSunday = nowLocalDate.with(TemporalAdjusters.previousOrSame(DayOfWeek.SUNDAY));
        // 上一个或者相同的星期六 2023-01-30
        LocalDate previousOrSameMonday = nowLocalDate.with(TemporalAdjusters.previousOrSame(DayOfWeek.MONDAY));

        // 自定义
        // 加两天 2023-02-07
        LocalDate plus2Days = nowLocalDate.with(TemporalAdjusters.ofDateAdjuster(date -> date.plus(2, ChronoUnit.DAYS)));


        System.out.println("nowLocalDate: " + nowLocalDate);
        System.out.println("thirdSundayOfMonth: " + thirdSundayOfMonth);
        System.out.println("firstDayOfMonth: " + firstDayOfMonth);
        System.out.println("firstDayOfNextMonth: " + firstDayOfNextMonth);
        System.out.println("firstDayOfYear: " + firstDayOfYear);
        System.out.println("firstDayOfNextYear: " + firstDayOfNextYear);
        System.out.println("firstSundayOfMonth: " + firstSundayOfMonth);
        System.out.println("lastDayOfMonth: " + lastDayOfMonth);
        System.out.println("lastDayOfYear: " + lastDayOfYear);
        System.out.println("lastSundayOfMonth: " + lastSundayOfMonth);
        System.out.println("nextSunday: " + nextSunday);
        System.out.println("nextOfSameSunday: " + nextOfSameSunday);
        System.out.println("nextOfSameMonday: " + nextOfSameMonday);
        System.out.println("previousSunday: " + previousSunday);
        System.out.println("previousOrSameSunday: " + previousOrSameSunday);
        System.out.println("previousOrSameMonday: " + previousOrSameMonday);
        System.out.println("plus2Days: " + plus2Days);
    }

根据LocalDate获取具体Time或者时间戳

可以通过LocalDate.atTime()获取具体的时间。如

• LocalDate.atTime(LocalTime.MIN) 获取当天最小时间 00:00:00
• LocalDate.atTime(LocalTime.MAX) 获取当天最大时间 23:59:59
• LocalDate.atTime(LocalTime.NOON) 获取当天中午时间 12:00

eg.

    public static void dateAndTimeUsage() {
        LocalDate nowLocalDate = LocalDate.now();
        // 2023-02-05
        System.out.println("nowLocalDate: " + nowLocalDate);
        LocalDateTime minLocalDateTime = nowLocalDate.atTime(LocalTime.MIN);
        // 2023-02-05T00:00
        System.out.println("minLocalDateTime: " + minLocalDateTime);
        LocalDateTime maxLocalDateTime = nowLocalDate.atTime(LocalTime.MAX);
        // 2023-02-05T23:59:59.999999999
        System.out.println("maxLocalDateTime: " + maxLocalDateTime);
        LocalDateTime noonLocalDateTime = nowLocalDate.atTime(LocalTime.NOON);
        // 2023-02-05T12:00
        System.out.println("noonLocalDateTime: " + noonLocalDateTime);
        // 获取时间戳
        // 1675526400000
        long minTimeStamp = minLocalDateTime.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
        System.out.println(minTimeStamp);
        // 1675612799999
        long maxTimeStamp = maxLocalDateTime.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
        System.out.println(maxTimeStamp);
        // 1675569600000
        long noonTimeStamp = noonLocalDateTime.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
        System.out.println(noonTimeStamp);
    }

结合LocalDate的with常用函数，就可以获取常用时间的时间戳：

eg.

• 某天的0点的时间戳
• 某天的23:59:59的时间戳
• 某周/月/年第一天的0点的时间戳
• 某周/月/年最后一天23:59:59的时间戳

eg.

    public static void commonTimestamp() {
        LocalDate nowLocalDate = LocalDate.now();
        // 2023-02-05
        System.out.println("nowLocalDate: " + nowLocalDate);
        // 1675526400000
        long minTimeStamp = nowLocalDate.atTime(LocalTime.MIN).atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
        // 1675612799999
        long maxTimeStamp = nowLocalDate.atTime(LocalTime.MAX).atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
        // 1675180800000
        long firstDayOfMonthMinTimeStamp = nowLocalDate.with(TemporalAdjusters.firstDayOfMonth()).atTime(LocalTime.MIN).atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
        // 1675267199999
        long firstDayOfMonthMaxTimeStamp = nowLocalDate.with(TemporalAdjusters.firstDayOfMonth()).atTime(LocalTime.MAX).atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
        System.out.println("minTimeStamp: " + minTimeStamp);
        System.out.println("maxTimeStamp: " + maxTimeStamp);
        System.out.println("firstDayOfMonthMinTimeStamp: " + firstDayOfMonthMinTimeStamp);
        System.out.println("firstDayOfMonthMaxTimeStamp: " + firstDayOfMonthMaxTimeStamp);
    }

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