20191227 Java8 日期时间API

Posted 2021-03-19 流星<。)#)))≦

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背景

Java 8通过发布新的Date-Time API (JSR 310)来进一步加强对日期与时间的处理。

在旧版的 Java 中，日期时间 API 存在诸多问题，其中有：

非线程安全 − java.util.Date 是非线程安全的，所有的日期类都是可变的，这是Java日期类最大的问题之一。
设计很差 − Java的日期/时间类的定义并不一致，在java.util和java.sql的包中都有日期类，此外用于格式化和解析的类在java.text包中定义。java.util.Date同时包含日期和时间，而java.sql.Date仅包含日期，将其纳入java.sql包并不合理。另外这两个类都有相同的名字，这本身就是一个非常糟糕的设计。
时区处理麻烦 − 日期类并不提供国际化，没有时区支持，因此Java引入了java.util.Calendar和java.util.TimeZone类，但他们同样存在上述所有的问题。

Java 8 在 java.time 包下提供了很多新的 API。以下为两个比较重要的 API：

Local(本地) − 简化了日期时间的处理，没有时区的问题。
Zoned(时区) − 通过制定的时区处理日期时间。

新的java.time包涵盖了所有处理日期，时间，日期/时间，时区，时刻（instants），过程（during）与时钟（clock）的操作。

LocalDateTime, LocalDate, LocalTime

这三者是本地化日期时间API

LocalDateTime 包含日期和时间，比如：2018-09-24 10:32:10
LocalDate 只包含日期，比如：2018-09-24
LocalTime 只包含时间，比如：10:32:10

private void testLocalDateTime() {

    System.out.println("=================== testLocalDateTime ============================");

    // 获取当前的日期时间
    LocalDateTime localDateTime = LocalDateTime.now();
    System.out.println("当前日期时间: " + localDateTime);
    System.out.println("当前日期: " + localDateTime.toLocalDate());
    System.out.println("当前时间: " + localDateTime.toLocalTime());

    System.out.println(",================== get =============================");
    // get
    // 获取日期时间的单项值
    int year = localDateTime.get(ChronoField.YEAR);
    Month month = localDateTime.getMonth();
    int monthValue = localDateTime.getMonthValue();
    int dayOfYear = localDateTime.getDayOfYear();
    int dayOfMonth = localDateTime.getDayOfMonth();
    DayOfWeek dayOfWeek = localDateTime.getDayOfWeek();
    int hour = localDateTime.getHour();
    int minute = localDateTime.getMinute();
    int seconds = localDateTime.getSecond();
    int nano = localDateTime.getNano();

    System.out.println("year：" + year);
    System.out.println("month：" + month);
    System.out.println("monthValue：" + monthValue);
    System.out.println("dayOfYear：" + dayOfYear);
    System.out.println("dayOfMonth：" + dayOfMonth);
    System.out.println("dayOfWeek：" + dayOfWeek);
    System.out.println("hour：" + hour);
    System.out.println("minute：" + minute);
    System.out.println("seconds：" + seconds);
    System.out.println("nano：" + nano);

    System.out.println(",================== with, plus, minus =============================");

    LocalDateTime withDateTime = localDateTime.with(ChronoField.YEAR, 2000).withMonth(10);
    System.out.println("withDateTime: " + withDateTime);

    LocalDateTime plusLocalDateTime = localDateTime.plus(1, ChronoUnit.MONTHS);
    System.out.println("plusLocalDateTime: " + plusLocalDateTime);

    LocalDateTime minusLocalDateTime = localDateTime.minusDays(1);
    System.out.println("minusLocalDateTime: " + minusLocalDateTime);

    System.out.println(",================== of =============================");
    // of
    // 通过指定值获取指定日期
    LocalDateTime ofLocalDateTime = LocalDateTime.of(2019, 12, 27, 15, 8, 7);
    System.out.println("ofLocalDateTime：" + ofLocalDateTime);

    LocalDate ofLocalDate = LocalDate.of(2014, Month.DECEMBER, 12);
    System.out.println("ofLocalDate: " + ofLocalDate);

    LocalTime ofLocalTime = LocalTime.of(22, 15);
    System.out.println("ofLocalTime: " + ofLocalTime);


    System.out.println(",================== parse =============================");
    // parse
    // 将字符串解析为日期、时间
    LocalDateTime parseDateTime = LocalDateTime.parse("2019-11-01T20:15:30.001");
    System.out.println("parseDateTime: " + parseDateTime);

    LocalDate parseDate = LocalDate.parse("2019-11-01");
    System.out.println("parseDate: " + parseDate);

    LocalTime parseTime = LocalTime.parse("20:15:30");
    System.out.println("parseTime: " + parseTime);

    System.out.println(",================== isAfter, isBefore =============================");
    boolean isAfter = localDateTime.isAfter(localDateTime.minusDays(1));
    System.out.println("isAfter: " + isAfter);

    boolean isBefore = localDateTime.isBefore(localDateTime.minusDays(1));
    System.out.println("isBefore: " + isBefore);

    System.out.println("================== LocalDate =============================");

    LocalDate localDate = LocalDate.now();
    System.out.println("localDate：" + localDate);

    int lengthOfMonth = localDate.lengthOfMonth();
    System.out.println("该月天数：" + lengthOfMonth);

    boolean isLeapYear = localDate.isLeapYear(); // false
    System.out.println("是否闰年：" + isLeapYear);

    LocalDateTime dateTime = localDate.atTime(5, 6);
    System.out.println("转为LocalDateTime：" + dateTime);

    System.out.println("================== LocalTime =============================");

    LocalTime localTime = LocalTime.now();
    System.out.println("localTime：" + localTime);

    LocalDateTime localDateTime1 = localTime.atDate(localDate);
    System.out.println("转为LocalDateTime：" + localDateTime1);


}

ZonedDateTime

带时区的日期时间

private void testZonedDateTime() {

    System.out.println("=================== testZonedDateTime ============================");

    // 获取当前时间日期
    ZonedDateTime date1 = ZonedDateTime.parse("2015-12-03T10:15:30+05:30[Asia/Shanghai]");
    System.out.println("date1: " + date1);

    ZoneId id = ZoneId.of("Europe/Paris");
    System.out.println("ZoneId: " + id);

    ZoneId currentZone = ZoneId.systemDefault();
    System.out.println("当期时区: " + currentZone);
}

MonthDay

MonthDay只包含月日信息，可以用于存放类似于生日，结婚纪念日等信息。

private void testMonthDay() {
    System.out.println("=================== testMonthDay ============================");

    LocalDate birthday = LocalDate.of(1999, 12, 27);
    MonthDay monthDay = MonthDay.of(birthday.getMonth(), birthday.getDayOfMonth());

    System.out.println("monthDay：" + monthDay);

    MonthDay fromMonthDay = MonthDay.from(LocalDate.now());
    System.out.println("MonthDay.from(LocalDate.now())：" + fromMonthDay);


    if (fromMonthDay.equals(monthDay)) {
        System.out.println("happy birthday!");
    } else {
        System.out.println("not birthday!");
    }
}

Period

Period用于计算两个LocalDate之间的时长。

private void testPeriod() {
    System.out.println("=================== testPeriod ============================");


    LocalDate date1 = LocalDate.of(2018, 9, 30);
    LocalDate date2 = LocalDate.of(2018, 10, 31);

    Period period = Period.between(date1, date2);
    System.out.println("period：" + period);

    List<TemporalUnit> units = period.getUnits();
    System.out.println("units：" + units);

    int months = period.getMonths();
    int days = period.getDays();

    System.out.println("months：" + months);
    System.out.println("days：" + days);

}

Duration

Duration用于计算两个LocalTime或者LocalDateTime的时间差。

private void testDuration() {
    System.out.println("=================== testDuration ============================");

    LocalDateTime dateTime1 = LocalDateTime.now();
    LocalDateTime dateTime2 = LocalDateTime.now().plusSeconds(60 * 60 * 2 + 1).minusNanos(1000000);

    Duration duration = Duration.between(dateTime1, dateTime2);
    System.out.println("duration：" + duration);

    List<TemporalUnit> units = duration.getUnits();
    System.out.println("duration.getUnits()：" + units);

    long seconds = duration.getSeconds();
    System.out.println("duration.getSeconds()：" + seconds);

    long nano = duration.getNano();
    System.out.println("duration.getNano()：" + nano);

    boolean isZero = duration.isZero();
    System.out.println("duration.isZero()：" + isZero);

    long hours = duration.toHours();
    System.out.println("duration.toHours()：" + hours);

    Duration abs = duration.abs();
    System.out.println("duration.abs()：" + abs);

    boolean isNegative = duration.isNegative();
    System.out.println("duration.isNegative()：" + isNegative);

    Duration withDuration = duration.withSeconds(5);
    System.out.println("duration.withSeconds(5)：" + withDuration);

    Duration plusNanos = duration.plusNanos(1000000);
    System.out.println("duration.plusNanos(1000000)：" + plusNanos);

}

Instant

时间戳。

private void testInstant() {
    System.out.println("=================== testInstant ============================");

    Instant instant = Instant.now();
    System.out.println("instant：" + instant);

    // 获取毫秒数
    long toEpochMilli = instant.toEpochMilli();
    System.out.println("toEpochMilli：" + toEpochMilli);

}

Clock

Clock 通过指定一个时区，然后就可以获取到当前的时刻，日期与时间。可以替代 System.currentTimeMillis() 与 TimeZone.getDefault() 。

private void testClock() {
    System.out.println("=================== testClock ============================");

    Clock clock = Clock.systemDefaultZone();
    System.out.println("Clock.systemDefaultZone()：" + clock);

    Instant instant = clock.instant();
    System.out.println("clock.instant()：" + instant);

}

ZoneId, ZoneOffset, ZoneRegion

对时区的操作。

ZoneId是抽象类，是ZoneOffset和ZoneRegion的父类。

private void testZone() {
    System.out.println("=================== testZone ============================");

    System.out.println(",=================== ZoneId ============================");

    Set<String> set = ZoneId.getAvailableZoneIds();
    System.out.println("ZoneId.getAvailableZoneIds()：" + Arrays.toString(set.toArray()));

    System.out.println(",,=================== ZoneOffset ============================");

    ZoneId systemDefaultZoneId = ZoneId.systemDefault();
    System.out.println("ZoneId.systemDefault()：" + systemDefaultZoneId);

    ZoneId ofZoneId = ZoneId.of("Asia/Aden");
    System.out.println("ofZoneId.getClass()：" + ofZoneId.getClass());
    System.out.println("ZoneId.of(\\"Asia/Aden\\")：" + ofZoneId);


    System.out.println(",,=================== ZoneRegion ============================");

    ZoneId ofZoneRegion = ZoneId.of("+8");
    System.out.println("ofZoneRegion.getClass()：" + ofZoneRegion.getClass());
    System.out.println("ZoneId.of(\\"+8\\")：" + ofZoneRegion);


}

TemporalAdjuster, TemporalAdjusters

用于调整日期时间。

TemporalAdjuster 是函数式接口，TemporalAdjusters 是工具类。

private void testTemporalAdjusters() {
    System.out.println("=================== testTemporalAdjusters ============================");

    LocalDateTime localDateTime = LocalDateTime.now();
    System.out.println("当前时间：" + localDateTime);

    TemporalAdjuster temporalAdjuster = null;

    System.out.println("=================== first, last ============================");

    temporalAdjuster = TemporalAdjusters.firstInMonth(DayOfWeek.FRIDAY);
    this.adjustDateTime("当月的第一个星期五", temporalAdjuster);

    temporalAdjuster = TemporalAdjusters.firstDayOfMonth();
    this.adjustDateTime("当月的第一天", temporalAdjuster);

    temporalAdjuster = TemporalAdjusters.firstDayOfNextMonth();
    this.adjustDateTime("下个月的第一天", temporalAdjuster);

    temporalAdjuster = TemporalAdjusters.lastInMonth(DayOfWeek.FRIDAY);
    this.adjustDateTime("当月的最后一个星期五", temporalAdjuster);

    temporalAdjuster = TemporalAdjusters.lastDayOfMonth();
    this.adjustDateTime("当月的最后一天", temporalAdjuster);

    temporalAdjuster = TemporalAdjusters.lastDayOfYear();
    this.adjustDateTime("当年的最后一天", temporalAdjuster);

    System.out.println("=================== next, previous ============================");

    // next：如果当天是周五，返回下一个周五
    // nextOrSame：如果当天是周五，返回当天
    temporalAdjuster = TemporalAdjusters.next(DayOfWeek.FRIDAY);
    this.adjustDateTime("下一个周五", temporalAdjuster);

    temporalAdjuster = TemporalAdjusters.nextOrSame(DayOfWeek.FRIDAY);
    this.adjustDateTime("下一个周五", temporalAdjuster);

    // previous：如果当天是周五，返回上一个周五
    // previousOrSame：如果当天是周五，返回当天
    temporalAdjuster = TemporalAdjusters.previous(DayOfWeek.FRIDAY);
    this.adjustDateTime("上一个周五", temporalAdjuster);

    temporalAdjuster = TemporalAdjusters.previousOrSame(DayOfWeek.FRIDAY);
    this.adjustDateTime("上一个周五", temporalAdjuster);

    System.out.println("=================== dayOfWeekInMonth ============================");

    temporalAdjuster = TemporalAdjusters.dayOfWeekInMonth(3, DayOfWeek.SUNDAY);
    this.adjustDateTime("当月的第三个星期日", temporalAdjuster);

    System.out.println("=================== ofDateAdjuster ============================");

    temporalAdjuster = TemporalAdjusters.ofDateAdjuster(localDate -> localDate.minusDays(1));
    this.adjustDateTime("昨天", temporalAdjuster);
}

private void adjustDateTime(String desc, TemporalAdjuster temporalAdjuster) {
    LocalDateTime localDateTime = LocalDateTime.now();
    LocalDateTime with = localDateTime.with(temporalAdjuster);
    System.out.println(desc + "：" + with);
}

DateTimeFormatter

用于格式化日期时间

private void testDateTimeFormatter() {
    System.out.println("=================== testDateTimeFormatter ============================");

    DateTimeFormatter dateTimeFormatter = null;

    System.out.println(",=================== ofLocalizedDateTime ============================");

    // FormatStyle.FULL 带时区信息，不能用于 LocalDateTime
    dateTimeFormatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.FULL);
    this.formatDateTime("ofLocalizedDateTime(FormatStyle.FULL)：", dateTimeFormatter);

    dateTimeFormatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.LONG);
    this.formatDateTime("ofLocalizedDateTime(FormatStyle.LONG)：", dateTimeFormatter);

    dateTimeFormatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM);
    this.formatDateTime("ofLocalizedDateTime(FormatStyle.MEDIUM)：", dateTimeFormatter);

    dateTimeFormatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.SHORT);
    this.formatDateTime("ofLocalizedDateTime(FormatStyle.SHORT)：", dateTimeFormatter);


    System.out.println(",=================== ofPattern ============================");

    dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy MM dd");
    this.formatDateTime("ofPattern(\\"yyyy MM dd\\")：", dateTimeFormatter);

    System.out.println(",=================== 静态常量 DateTimeFormatter ============================");

    dateTimeFormatter = DateTimeFormatter.BASIC_ISO_DATE;
    this.formatDateTime("BASIC_ISO_DATE：", dateTimeFormatter);

    dateTimeFormatter = DateTimeFormatter.ISO_DATE_TIME;
    this.formatDateTime("ISO_DATE_TIME：", dateTimeFormatter);


}

private void formatDateTime(String desc, DateTimeFormatter dateTimeFormatter) {
    ZonedDateTime zonedDateTime = ZonedDateTime.now();
    String format = zonedDateTime.format(dateTimeFormatter);
    System.out.println(desc + "：" + format);
}

与 java.util.Date 的相互转换

private void testConvert() {
    System.out.println("=================== testConvert ============================");

    System.out.println(",=================== LocalDateTime 转 java.util.Date ============================");

    LocalDateTime localDateTime = LocalDateTime.now();
    System.out.println("localDateTime：" + localDateTime);
    Instant instant = localDateTime.atZone(ZoneId.systemDefault()).toInstant();
    Date fromDate = Date.from(instant);
    System.out.println("fromDate：" + fromDate);

    System.out.println(",=================== java.util.Date 转 LocalDateTime ============================");
    Date date = new Date();
    System.out.println("date：" + date);
    Instant toInstant = date.toInstant();
    LocalDateTime ofLocalDateTime = LocalDateTime.ofInstant(toInstant, ZoneId.systemDefault());
    System.out.println("ofLocalDateTime：" + ofLocalDateTime);
}

参考资料

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