java 8 Date & Time

文章目录

• Local Date-Time 的简单使用
• Zoned 的简单使用
• Chrono Units Enum
• Period and Duration
• Backward Compatibility

Java 8 之前使用的时间类：Date存在缺点：

Not thread safe - java.util.Date是非线程安全的，使用时必须处理并发问题。而新的时间类是不可变的，并且没有 set 方法。
Poor design - java.util.Date中日期从1900开始，月从1开始，天从0开始，十分不统一；原来的API提供了很少的时间操作。
Difficult time zone handing - 原来的API需要花费大量代码处理区域时间。

Java 8 加入了新的API：java.time

Java.time包中的是类是不可变且线程安全的。新的时间及日期API位于java.time中

• Local - 简单时间API
• Zoned - 区域时间API

* Instance 			    时间戳
* LocalDate			    不包含时间的日期
* LocalTime 			不包含日期的时间
* LocalDateTime 		包含时间及日期（没有偏移信息/时区）
* ZonedDateTime 		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。

Local Date-Time 的简单使用

    public String Local() {
        //获取当前日期时间
        LocalDateTime currentTime = LocalDateTime.now();
        System.out.println("当前时间:"+currentTime);
        
        LocalDate date1 = currentTime.toLocalDate();
        System.out.println("date1:"+ date1);

        Month month = currentTime.getMonth();
        int day = currentTime.getDayOfMonth();
        int seconds = currentTime.getSecond();
        System.out.println("月: " + month +", 日: " + day +", 秒: " + seconds);

        //给定了日期与年份 date2:2012-12-10T16:10:38.992224100
        LocalDateTime date2 = currentTime.withDayOfMonth(10).withYear(2012);
        System.out.println("date2:"+ date2);

        //给定日期 date3:2014-12-12
        LocalDate date3 = LocalDate.of(2014, Month.DECEMBER,12);
        System.out.println("date3:"+ date3);

        //给定时间 date4:22:15
        LocalTime date4 = LocalTime.of(22,15);
        System.out.println("date4:" + date4);

        //解析字符串 date5:20:15:30
        LocalTime date5 = LocalTime.parse("20:15:30");
        System.out.println("date5:" + date5);
        
        return "1";
    }

运行结果

当前时间:2019-12-18T16:10:38.992224100
date1:2019-12-18
月: DECEMBER, 日: 18, 秒: 38
date2:2012-12-10T16:10:38.992224100
date3:2014-12-12
date4:22:15
date5:20:15:30

Zoned 的简单使用

 	public String Zoned() {
        //获取当前时间日期
        //date1:2012-12-12T13:05:10+08:00[Asia/Shanghai]
        ZonedDateTime date1 = ZonedDateTime.parse("2012-12-12T10:10:10+05:05[Asia/Shanghai]");
        System.out.println("date1:"+date1);

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

        //Asia/Shanghai
        ZoneId currentZone = ZoneId.systemDefault();
        System.out.println(currentZone);
        return "2";
    }

运行结果：

date1:2012-12-12T13:05:10+08:00[Asia/Shanghai]
ZoneId:Europe/Paris
Asia/Shanghai

Chrono Units Enum

java.time.temporal.ChronoUnit枚举类用来用表示年、月、日等，这取代原来使用 int值来表示

	public String ChronoUnit() {
        //Get the current date
        LocalDate today = LocalDate.now();
        System.out.println("Current date: " + today);

        //add 1 week to the current date
        LocalDate nextWeek = today.plus(1, ChronoUnit.WEEKS);
        System.out.println("Next week: " + nextWeek);

        //add 1 month to the current date
        LocalDate nextMonth = today.plus(1, ChronoUnit.MONTHS);
        System.out.println("Next month: " + nextMonth);

        //add 1 year to the current date
        LocalDate nextYear = today.plus(1, ChronoUnit.YEARS);
        System.out.println("Next year: " + nextYear);

        //add 10 years to the current date
        LocalDate nextDecade = today.plus(1, ChronoUnit.DECADES);
        System.out.println("Date after ten year: " + nextDecade);
        return null;
    }

运行结果：

Current date: 2019-12-18
Next week: 2019-12-25
Next month: 2020-01-18
Next year: 2020-12-18
Date after ten year: 2029-12-18

Period and Duration

Java 8 中两个类Period和Duration处理时间差：

• Period - 处理日期差。
• Duration - 处理时间差。

public String pd() {
        /*****testPeriod*****/
        //Get the current date
        LocalDate date1 = LocalDate.now();
        System.out.println("Current date: " + date1);

        //add 1 month to the current date
        LocalDate date2 = date1.plus(1, ChronoUnit.MONTHS);
        System.out.println("Next month: " + date2);

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

        /*****testDuration*****/
        LocalTime time1 = LocalTime.now();
        Duration twoHours = Duration.ofHours(2);

        LocalTime time2 = time1.plus(twoHours);
        Duration duration = Duration.between(time1, time2);

        System.out.println("Duration: " + duration);
        return null;
    }

运行结果：

Current date: 2019-12-18
Next month: 2020-01-18
Period: P-1M
Duration: PT2H

Backward Compatibility

toInstant()方法用来将老的Date对象转换为LocalDateTime或ZonedDateTime对象

public String testBackwardCompatability() {
        //Get the current date
        Date currentDate = new Date();
        System.out.println("Current date: " + currentDate);

        //Get the instant of current date in terms of milliseconds
        Instant now = currentDate.toInstant();
        ZoneId currentZone = ZoneId.systemDefault();

        LocalDateTime localDateTime = LocalDateTime.ofInstant(now, currentZone);
        System.out.println("Local date: " + localDateTime);

        ZonedDateTime zonedDateTime = ZonedDateTime.ofInstant(now, currentZone);
        System.out.println("Zoned date: " + zonedDateTime);
        return null;
    }

运行结果：

Current date: Wed Dec 18 16:38:04 CST 2019
Local date: 2019-12-18T16:38:04.741
Zoned date: 2019-12-18T16:38:04.741+08:00[Asia/Shanghai]

参考文档：https://blog.csdn.net/weixin_37547589/article/details/90064465

来源：CSDN

作者：LuckyGuyy

链接：https://blog.csdn.net/qq_36821220/article/details/103598823