Java8新特性之新的日期时间类（八）

1. 背景介绍

在Java8之前，Date和Calendar两个类占据了Java中对时间操作的几乎所有地方，但由于它们的可变性和非线程安全性也时常导致了一些bug的产生；所以在Java8中引入了新的日期时间相关类，放在java.time包下；

2. 新日期时间相关类介绍

• LocalDate：本地日期，不包含时区；

• LocalTime：本地时间，不包含时区；

• LocalDateTime：本地日期+时间，内部维护者一对LocalDate与LocalTime实例，同时也不包含时区；

• ZoneId：时区标识符，是Instant和LocalDateTime之间转换的规则；

• ZoneOffset：格林威治/UTC时间之间的时区偏移量；

• ZonedDateTime：一个包含得有时区标识符和时区偏移量的日期+时间类，内部维护者LocalDateTime、ZoneId、ZoneOffset三个实例；

• Instant：一个可以精确到纳秒的时间戳类；

• DateTimeFormatter：日期时间格式化与解析类；

3. 新日期时间常用API介绍

1. LocalDate

public class LocalDateTimeTest {

    public static void main(String[] args) {
        // 获取当前日期
        LocalDate date1 = LocalDate.now();
        System.out.println("date1: " + date1);
        System.out.println("date1 year: " + date1.getYear());
        System.out.println("date1 month: " + date1.getMonthValue());
        System.out.println("date1 day: " + date1.getDayOfMonth());
        // 创建LocalDate实例
        LocalDate date2 = LocalDate.of(2021, 1, 1);
        System.out.println("date2: " + date2);
        // 修改LocalDate实例, 返回一个新的实例
        LocalDate date3 = date2.plus(7, ChronoUnit.DAYS);
        System.out.println("date3: " + date3);
        // 解析日期字符串
        LocalDate date4 = LocalDate.parse("20210131", DateTimeFormatter.ofPattern("yyyyMMdd"));
        System.out.println("date4: " + date4);
    }
}

// 运行结果
date1: 2021-04-20
date1 year: 2021
date1 month: 4
date1 day: 20
date2: 2021-01-01
date3: 2021-01-08
date4: 2021-01-31

2. LocalTime

public class LocalDateTimeTest {

    public static void main(String[] args) {
        // 获取当前时间
        LocalTime time1 = LocalTime.now();
        System.out.println("time1: " + time1);
        System.out.println("time1 hour: " + time1.getHour());
        System.out.println("time1 minute: " + time1.getMinute());
        System.out.println("time1 second: " + time1.getSecond());
        System.out.println("time1 nano: " + time1.getNano());
        // 创建LocalTime实例
        LocalTime time2 = LocalTime.of(8, 8, 8);
        System.out.println("time2: " + time2);
        // 修改LocalTime实例, 返回一个新的实例
        LocalTime time3 = time2.plus(7, ChronoUnit.MINUTES);
        System.out.println("time3: " + time3);
        // 解析时间字符串
        LocalTime time4 = LocalTime.parse("12:30:10", DateTimeFormatter.ofPattern("HH:mm:ss"));
        System.out.println("time4: " + time4);
    }
}

// 运行结果
time1: 14:20:35.276
time1 hour: 14
time1 minute: 20
time1 second: 35
time1 nano: 276000000
time2: 08:08:08
time3: 08:15:08
time4: 12:30:10

3. LocalDateTime

public class LocalDateTimeTest {

    public static void main(String[] args) {
        // 获取当前日期时间
        LocalDateTime dateTime1 = LocalDateTime.now();
        System.out.println("dateTime1: " + dateTime1);
        // 创建LocalDateTime实例
        LocalDateTime dateTime2 = LocalDateTime.of(2021, 4, 20, 14, 23, 1);
        System.out.println("dateTime2: " + dateTime2);
        // 解析日期时间对象
        LocalDateTime dateTime3 = LocalDateTime.parse("2021-04-20 14:30:00", DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
        System.out.println("dateTime3: " + dateTime3);
        // 修改LocalDateTime实例, 返回一个新的实例
        LocalDateTime dateTime4 = dateTime3.withMonth(5);
        System.out.println("dateTime4: " + dateTime4.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));
    }
}

// 运行结果
dateTime1: 2021-04-20T14:33:10.264
dateTime2: 2021-04-20T14:23:01
dateTime3: 2021-04-20T14:30
dateTime4: 2021-05-20 14:30:00

4. ZonedDateTime

public class LocalDateTimeTest {

    public static void main(String[] args) {
        // 获取当前日期时间+时区
        ZonedDateTime dateTime1 = ZonedDateTime.now();
        System.out.println("dateTime1: " + dateTime1);
        // 创建ZonedDateTime实例
        LocalDate date = LocalDate.of(2021, 4, 20);
        LocalTime time = LocalTime.of(14, 30, 30);
        ZonedDateTime dateTime2 = ZonedDateTime.of(LocalDateTime.of(date, time), ZoneId.of("Asia/Shanghai"));
        System.out.println("dateTime2: " + dateTime2);
    }
}

// 运行结果
dateTime1: 2021-04-20T14:37:47.019+08:00[Asia/Shanghai]
dateTime2: 2021-04-20T14:30:30+08:00[Asia/Shanghai]

5. Instant

public class LocalDateTimeTest {

    public static void main(String[] args) {
        // 获取格林威治时间
        Instant instant1 = Instant.now();
        System.out.println("instant1: " + instant1);
        // Date转Instant
        Instant instant2 = new Date().toInstant();
        System.out.println("instant2: " + instant2);
        // Instant转ZonedDateTime
        ZonedDateTime dateTime1 = ZonedDateTime.ofInstant(instant2, ZoneId.of("Asia/Shanghai"));
        System.out.println("dateTime1: " + dateTime1);
        // Instant转LocalDateTime
        LocalDateTime dateTime2 = LocalDateTime.ofInstant(instant2, ZoneId.of("Asia/Shanghai"));
        System.out.println("dateTime2: " + dateTime2);
    }
}

// 运行结果
instant1: 2021-04-20T06:49:52.519Z
instant2: 2021-04-20T06:49:52.577Z
dateTime1: 2021-04-20T14:49:52.577+08:00[Asia/Shanghai]
dateTime2: 2021-04-20T14:49:52.577

4. 类型转换表

类	To遗留类	From遗留类
java.time.Instant java.util.Date	Date.from(instant)	date.toInstant()
java.time.Instant java.sql.Timestamp	Timestamp.from(instant)	timestamp.toInstant()
java.time.LocalDate java.sql.Date	Date.valueOf(localDate)	Date.toLocalDate()
java.time.LocalTime java.sql.Time	Time.valueOf(localTime)	Time.toLocalTime()
java.time.LocalDateTime java.sql.Timestamp	Timestamp.valueOf(localDateTime)	Timestamp.toLocalDateTime()

原文链接：https://blog.csdn.net/gu19930914/article/details/115907714