Java8 Date Time API

  1. 1. 为什么需要新的Date API
  2. 2. Java8 Date Time API 详解
    1. 2.1 Packages
    2. 2.2 LocalDate
    3. 2.3 LocalTime
    4. 2.4 LocalDateTime
    5. 2.5 Instant
    6. 2.6 常用API
    7. 2.7 时间的Parsing 和 Formatting
  3. Reference

1. 为什么需要新的Date API

Java8 的一大更新在于终于将Date Time一致化,这解决了在Java8以前我们观察到的非常多的问题:

譬如:

  • Java Date Time类定义在不同的地方,比如在java.util & java.sql里面都有,而样式和格式转化的类都定义在java.text的包里,比较混乱
  • java.util.Date包括date和time类,而java.sql.Date只包含date
  • 并没有清晰定义的类用于处理time, timestamp, formatting, parsing
  • 所有的Date类都是可变的,并不是线程安全的
  • Date类不支持全球化,没有时区的支持,在java8之前,为了显示当地时间,就得使用java.util.Calendar 还有 java.util.TimeZone,整个变得比较麻烦

2. Java8 Date Time API 详解

2.1 Packages

  • java.time Package
    • 这是新的Date Time API的基础包,一些主要的基本类都在这里面,譬如LocalDate, LocalTime, LocalDateTime, Instant, Period, Duration
  • java.time.chrono
    • 定义了抽象的API接口,针对于非ISO标准的calendar 系统,我们可以通过extend AbstractChronology类来创建我们自己的calendar系统
  • java.time.format
    • 包含用来Formatting还有parsing date time对象的类
  • java.time.temporal
    • 包含一些时间对象,比如找到月份的第一天, 最后一天之类的
  • java.time.zone
    • 支持不同的时区

2.2 LocalDate

  • Immutable class
  • 默认样式为 yyyy-MM-dd
  • 我们可以使用now()方法来获得当前的日期
  • 也可以通过提供年月日来创建localDate对象
  • 我们同时也可以传入ZoneId来得到在特定的时区的日期
package com.journaldev.java8.time;

import java.time.LocalDate;
import java.time.Month;
import java.time.ZoneId;

/**
 * LocalDate Examples
 * @author pankaj
 *
 */
public class LocalDateExample {

    public static void main(String[] args) {

        //Current Date
        LocalDate today = LocalDate.now();
        System.out.println("Current Date="+today);

        //Creating LocalDate by providing input arguments
        LocalDate firstDay_2014 = LocalDate.of(2014, Month.JANUARY, 1);
        System.out.println("Specific Date="+firstDay_2014);


        //Try creating date by providing invalid inputs
        //LocalDate feb29_2014 = LocalDate.of(2014, Month.FEBRUARY, 29);
        //Exception in thread "main" java.time.DateTimeException: 
        //Invalid date 'February 29' as '2014' is not a leap year

        //Current date in "Asia/Kolkata", you can get it from ZoneId javadoc
        LocalDate todayKolkata = LocalDate.now(ZoneId.of("Asia/Kolkata"));
        System.out.println("Current Date in IST="+todayKolkata);

        //java.time.zone.ZoneRulesException: Unknown time-zone ID: IST
        //LocalDate todayIST = LocalDate.now(ZoneId.of("IST"));

        //Getting date from the base date i.e 01/01/1970
        LocalDate dateFromBase = LocalDate.ofEpochDay(365);
        System.out.println("365th day from base date= "+dateFromBase);

        LocalDate hundredDay2014 = LocalDate.ofYearDay(2014, 100);
        System.out.println("100th day of 2014="+hundredDay2014);
    }

}



// output 
Current Date=2014-04-28
Specific Date=2014-01-01
Current Date in IST=2014-04-29
365th day from base date= 1971-01-01
100th day of 2014=2014-04-10

2.3 LocalTime

  • Immutable Class
  • 表示一个可读的时间 (vs Instant 基本不可读)
  • 默认样式为 hh:mm:ss:zz
  • 和LocalDate基本一致的用法,可以传入参数生成实例,支持时区
package com.journaldev.java8.time;

import java.time.LocalTime;
import java.time.ZoneId;

/**
 * LocalTime Examples
 * @author pankaj
 *
 */
public class LocalTimeExample {

    public static void main(String[] args) {

        //Current Time
        LocalTime time = LocalTime.now();
        System.out.println("Current Time="+time);

        //Creating LocalTime by providing input arguments
        LocalTime specificTime = LocalTime.of(12,20,25,40);
        System.out.println("Specific Time of Day="+specificTime);

        //Try creating time by providing invalid inputs
        //LocalTime invalidTime = LocalTime.of(25,20);
        //Exception in thread "main" java.time.DateTimeException: 
        //Invalid value for HourOfDay (valid values 0 - 23): 25

        //Current date in "Asia/Kolkata", you can get it from ZoneId javadoc
        LocalTime timeKolkata = LocalTime.now(ZoneId.of("Asia/Kolkata"));
        System.out.println("Current Time in IST="+timeKolkata);

        //java.time.zone.ZoneRulesException: Unknown time-zone ID: IST
        //LocalTime todayIST = LocalTime.now(ZoneId.of("IST"));

        //Getting date from the base date i.e 01/01/1970
        LocalTime specificSecondTime = LocalTime.ofSecondOfDay(10000);
        System.out.println("10000th second time= "+specificSecondTime);

    }
}


// Output 
Current Time=15:51:45.240
Specific Time of Day=12:20:25.000000040
Current Time in IST=04:21:45.276
10000th second time= 02:46:40

2.4 LocalDateTime

  • Immutable date-time object
  • represent both date and time
  • default format at yyyy-MM-dd-HH-mm-ss.zzz
  • 用工厂方法来拿到LocalDate和LocalTime的input 然后来创建LocalDateTime的实例
package com.journaldev.java8.time;

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.Month;
import java.time.ZoneId;
import java.time.ZoneOffset;

public class LocalDateTimeExample {

    public static void main(String[] args) {

        //Current Date
        LocalDateTime today = LocalDateTime.now();
        System.out.println("Current DateTime="+today);

        //Current Date using LocalDate and LocalTime
        today = LocalDateTime.of(LocalDate.now(), LocalTime.now());
        System.out.println("Current DateTime="+today);

        //Creating LocalDateTime by providing input arguments
        LocalDateTime specificDate = LocalDateTime.of(2014, Month.JANUARY, 1, 10, 10, 30);
        System.out.println("Specific Date="+specificDate);


        //Try creating date by providing invalid inputs
        //LocalDateTime feb29_2014 = LocalDateTime.of(2014, Month.FEBRUARY, 28, 25,1,1);
        //Exception in thread "main" java.time.DateTimeException: 
        //Invalid value for HourOfDay (valid values 0 - 23): 25


        //Current date in "Asia/Kolkata", you can get it from ZoneId javadoc
        LocalDateTime todayKolkata = LocalDateTime.now(ZoneId.of("Asia/Kolkata"));
        System.out.println("Current Date in IST="+todayKolkata);

        //java.time.zone.ZoneRulesException: Unknown time-zone ID: IST
        //LocalDateTime todayIST = LocalDateTime.now(ZoneId.of("IST"));

        //Getting date from the base date i.e 01/01/1970
        LocalDateTime dateFromBase = LocalDateTime.ofEpochSecond(10000, 0, ZoneOffset.UTC);
        System.out.println("10000th second time from 01/01/1970= "+dateFromBase);

    }
}

// Output
Current DateTime=2014-04-28T16:00:49.455
Current DateTime=2014-04-28T16:00:49.493
Specific Date=2014-01-01T10:10:30
Current Date in IST=2014-04-29T04:30:49.493
10000th second time from 01/01/1970= 1970-01-01T02:46:40

2.5 Instant

是为了生成机器阅读的时间格式,它会使用unix的时间戳来存储日期和时间

package com.journaldev.java8.time;

import java.time.Duration;
import java.time.Instant;

public class InstantExample {

    public static void main(String[] args) {
        //Current timestamp
        Instant timestamp = Instant.now();
        System.out.println("Current Timestamp = "+timestamp);

        //Instant from timestamp
        Instant specificTime = Instant.ofEpochMilli(timestamp.toEpochMilli());
        System.out.println("Specific Time = "+specificTime);

        //Duration example
        Duration thirtyDay = Duration.ofDays(30);
        System.out.println(thirtyDay);
    }

}

// Output 
Current Timestamp = 2014-04-28T23:20:08.489Z
Specific Time = 2014-04-28T23:20:08.489Z
PT720H

2.6 常用API

package com.journaldev.java8.time;

import java.time.LocalDate;
import java.time.LocalTime;
import java.time.Period;
import java.time.temporal.TemporalAdjusters;

public class DateAPIUtilities {

    public static void main(String[] args) {

        LocalDate today = LocalDate.now();

        //得到年份,看是否为闰年
        System.out.println("Year "+today.getYear()+" is Leap Year? "+today.isLeapYear());

        //比较两个时间的先后
        System.out.println("Today is before 01/01/2015? "+today.isBefore(LocalDate.of(2015,1,1)));

        //从LocalDate创建LocalDateTime
        System.out.println("Current Time="+today.atTime(LocalTime.now()));

        //加减时间的操作
        System.out.println("10 days after today will be "+today.plusDays(10));
        System.out.println("3 weeks after today will be "+today.plusWeeks(3));
        System.out.println("20 months after today will be "+today.plusMonths(20));

        System.out.println("10 days before today will be "+today.minusDays(10));
        System.out.println("3 weeks before today will be "+today.minusWeeks(3));
        System.out.println("20 months before today will be "+today.minusMonths(20));

        //时间上的加减
        System.out.println("First date of this month= "+today.with(TemporalAdjusters.firstDayOfMonth()));
        LocalDate lastDayOfYear = today.with(TemporalAdjusters.lastDayOfYear());
        System.out.println("Last date of this year= "+lastDayOfYear);

        Period period = today.until(lastDayOfYear);
        System.out.println("Period Format= "+period);
        System.out.println("Months remaining in the year= "+period.getMonths());        
    }
}



Year 2014 is Leap Year? false
Today is before 01/01/2015? true
Current Time=2014-04-28T16:23:53.154
10 days after today will be 2014-05-08
3 weeks after today will be 2014-05-19
20 months after today will be 2015-12-28
10 days before today will be 2014-04-18
3 weeks before today will be 2014-04-07
20 months before today will be 2012-08-28
First date of this month= 2014-04-01
Last date of this year= 2014-12-31
Period Format= P8M3D
Months remaining in the year= 8

2.7 时间的Parsing 和 Formatting

package com.journaldev.java8.time;

import java.time.Instant;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

public class DateParseFormatExample {

    public static void main(String[] args) {

        //Format examples
        LocalDate date = LocalDate.now();
        //default format
        System.out.println("Default format of LocalDate="+date);
        //使用特定的Formatter
        System.out.println(date.format(DateTimeFormatter.ofPattern("d::MMM::uuuu")));
        System.out.println(date.format(DateTimeFormatter.BASIC_ISO_DATE));


        LocalDateTime dateTime = LocalDateTime.now();
        //default format
        System.out.println("Default format of LocalDateTime="+dateTime);
        //specific format
        System.out.println(dateTime.format(DateTimeFormatter.ofPattern("d::MMM::uuuu HH::mm::ss")));
        System.out.println(dateTime.format(DateTimeFormatter.BASIC_ISO_DATE));

        Instant timestamp = Instant.now();
        //default format
        System.out.println("Default format of Instant="+timestamp);

        //Parse examples
        LocalDateTime dt = LocalDateTime.parse("27::Apr::2014 21::39::48",
                DateTimeFormatter.ofPattern("d::MMM::uuuu HH::mm::ss"));
        System.out.println("Default format after parsing = "+dt);
    }

}


// Output

Default format of LocalDate=2014-04-28
28::Apr::2014
20140428
Default format of LocalDateTime=2014-04-28T16:25:49.341
28::Apr::2014 16::25::49
20140428
Default format of Instant=2014-04-28T23:25:49.342Z
Default format after parsing = 2014-04-27T21:39:48

Reference

  1. https://www.journaldev.com/2800/java-8-date-localdate-localdatetime-instant

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文章标题:Java8 Date Time API

文章字数:1.9k

本文作者:Leilei Chen

发布时间:2020-02-19, 19:08:47

最后更新:2020-02-19, 19:09:12

原始链接:https://www.llchen60.com/Java8-Date-Time-API/

版权声明: "署名-非商用-相同方式共享 4.0" 转载请保留原文链接及作者。

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