【Java】Java8新特性之时间和日期API

一、时间和日期API介绍

　　Java三次引入处理时间的API，JDK1.0中包含了一个Date类，但大多数方法在java1.1引入Calendear类之后被弃用了。 它的实例都是可变的，而且它的API很难使用，比如月份是从0开始这种反人类的设置。java8引入的java.time 包中 API 已经纠正了之前的问题。它已经完全实现了JSR310规范。

　　java8引入了一套全新的时间日期API，本篇随笔将说明学习java8的这套API。

　　java.time包中的是类是不可变(类似String类，改变后会新建一个对象)且线程安全的。新的时间及日期API位于java.time中，下面是一些关键类

　　●Instant——它代表的是时间戳

　　●LocalDate——不包含具体时间的日期，比如2014-01-14。它可以用来存储生日，周年纪念日，入职日期等。

　　●LocalTime——它代表的是不含日期的时间

　　●LocalDateTime——它包含了日期及时间，不过还是没有偏移信息或者说时区。

　　●ZonedDateTime——这是一个包含时区的完整的日期时间，偏移量是以UTC/格林威治时间为基准的。

二、常用时间日期类介绍

1、Instant 时间戳

// Instant：时间戳（以Unix元年：1970年1月1日 00:00:00.000 到某个时间之间的毫秒值）
@Test
public void test1() {
    // 当前时间戳
    Instant now = Instant.now();
    System.out.println("now = " + now);
    System.out.println("now.getEpochSecond() = " + now.getEpochSecond());
    System.out.println("now.toEpochMilli() = " + now.toEpochMilli());

    LocalDateTime time = LocalDateTime.of(1970, 1, 1, 0,0);
    System.out.println("time = " + time);
    Instant instant = time.toInstant(ZoneOffset.UTC);
    System.out.println("instant = " + instant);
    System.out.println("instant.toEpochMilli() = " + instant.toEpochMilli());
    System.out.println("instant.getEpochSecond() = " + instant.getEpochSecond());

    Instant instant1 = Instant.ofEpochSecond(60);
    System.out.println("instant1 = " + instant1);
}

2、LocalDate 本地日期

@Test
public void test1() {
    // 当前日期
    LocalDate localDate = LocalDate.now();
    System.out.println("localDate = " + localDate);

    LocalDateTime localDateTime = LocalDateTime.now();
    System.out.println("localDateTime = " + localDateTime);
    String s = localDateTime.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSS"));
    System.out.println("s = " + s);
}

3、LocalTime 本地时间

@Test
public void test1() {
    // 当前本地时间
    LocalTime now = LocalTime.now();
    System.out.println("now = " + now);
    
    LocalTime time = LocalTime.of(12, 30, 59);
    System.out.println("time = " + time);
    System.out.println("time.getHour() = " + time.getHour());
    System.out.println("time.getMinute() = " + time.getMinute());
    System.out.println("time.getSecond() = " + time.getSecond());
}

4、LocalDateTime 本地日期时间

@Test
public void test1() {
    LocalDate localDate = LocalDate.now();
    System.out.println("localDate = " + localDate);

    // 当前本地日期时间
    LocalDateTime localDateTime = LocalDateTime.now();
    System.out.println("localDateTime = " + localDateTime);
    String s = localDateTime.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSS"));
    System.out.println("s = " + s);
}

@Test
public void test2() {
    LocalDateTime dateTime = LocalDateTime.of(2024, 12, 4, 8, 9, 14);
    System.out.println("dateTime = " + dateTime);

    LocalDateTime dateTime1 = dateTime.plusYears(2);
    System.out.println("dateTime1 = " + dateTime1);

    LocalDateTime dateTime2 = dateTime.minusHours(2);
    System.out.println("dateTime2 = " + dateTime2);

    System.out.println(dateTime.getYear());
    System.out.println(dateTime.getMonth());
    System.out.println(dateTime.getDayOfMonth());
    System.out.println(dateTime.getHour());
    System.out.println(dateTime.getMinute());
    System.out.println(dateTime.getSecond());
}

// Instant：时间戳（以Unix元年：1970年1月1日 00:00:00.000 到某个时间之间的毫秒值）
@Test
public void test3() {
    Instant now = Instant.now();
    System.out.println("now = " + now);
    System.out.println("now.getEpochSecond() = " + now.getEpochSecond());
    System.out.println("now.toEpochMilli() = " + now.toEpochMilli());

    LocalDateTime time = LocalDateTime.of(1970, 1, 1, 0,0);
    System.out.println("time = " + time);
    Instant instant = time.toInstant(ZoneOffset.UTC);
    System.out.println("instant = " + instant);
    System.out.println("instant.toEpochMilli() = " + instant.toEpochMilli());
    System.out.println("instant.getEpochSecond() = " + instant.getEpochSecond());

    Instant instant1 = Instant.ofEpochSecond(60);
    System.out.println("instant1 = " + instant1);

}

5、ZonedDateTime 时区日期时间

 @Test
public void test1() {
    ZoneId.getAvailableZoneIds().stream().sorted()
            .forEach(System.out::println);
}

@Test
public void test2() {
    LocalDateTime now = LocalDateTime.now(ZoneId.of("Asia/Shanghai"));
    System.out.println("now = " + now);
    ZonedDateTime zonedDateTime = now.atZone(ZoneId.of("Asia/Shanghai"));
    System.out.println("zonedDateTime = " + zonedDateTime);

}

6、Duration 和 Period 时间间隔　　

　　Duration：计算两个“时间”之间的间隔

　　Period：计算两个“日期”之间的间隔

// Duration：计算两个“时间”之间的间隔
// Period：计算两个“日期”之间的间隔
@Test
public void test4() throws InterruptedException {
    Instant ins1 = Instant.now();
    System.out.println("ins1 = " + ins1);
    Thread.sleep(1234);
    Instant ins2 = Instant.now();
    System.out.println("ins2 = " + ins2);
    Duration between = Duration.between(ins1, ins2);
    System.out.println("between = " + between);
    System.out.println("between.toMillis() = " + between.toMillis());
    System.out.println("between.toNanos() = " + between.toNanos());



    LocalDateTime localDateTime1 = LocalDateTime.now();
    Thread.sleep(1234);
    LocalDateTime localDateTime2 = LocalDateTime.now();
    Duration between1 = Duration.between(localDateTime1, localDateTime2);
    System.out.println("between1 = " + between1);
    System.out.println("between1.toMillis() = " + between1.toMillis());

}

@Test
public void test5() throws InterruptedException {
    LocalDate localDate1 = LocalDate.now();
    Thread.sleep(1234);
    LocalDate localDate2 = LocalDate.of(2022,7,30);

    Period between = Period.between(localDate1, localDate2);
    System.out.println("between = " + between);
    System.out.println("between.toMillis() = " + between.getDays());
    System.out.println("between.getMonths() = " + between.getMonths());
    System.out.println("between.getYears() = " + between.getYears());
}

7、DateTimeFormatter 日期时间格式化

@Test
public void test1() {
    LocalDateTime now = LocalDateTime.now();
    DateTimeFormatter basicIsoDate = DateTimeFormatter.BASIC_ISO_DATE;

    String format1 = now.format(basicIsoDate);
    System.out.println("format1 = " + format1);

    String format2 = now.format(DateTimeFormatter.ISO_DATE_TIME);
    System.out.println("format2 = " + format2);

    DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    String format3 = now.format(dateTimeFormatter);
    System.out.println("format3 = " + format3);

    LocalDateTime parse = LocalDateTime.parse(format3, dateTimeFormatter);
    System.out.println("parse = " + parse);
}

8、TemporalAdjuster 时间调整器

// TemporalAdjuster 时间调整器
@Test
public void test6() {
    LocalDateTime dateTime = LocalDateTime.now();
    System.out.println("dateTime = " + dateTime);

    LocalDateTime dateTime1 = dateTime.withDayOfMonth(10);
    System.out.println("dateTime1 = " + dateTime1);

    // 使用时间调整器
    LocalDateTime dateTime2 = dateTime.with(TemporalAdjusters.firstDayOfMonth());
    System.out.println("dateTime2 = " + dateTime2);

    // 自定义时间调整器
    LocalDateTime dateTime3 = dateTime.with(time -> ((LocalDateTime) time).plusDays(8));
    System.out.println("dateTime3 = " + dateTime3);
}