Java8 Date Time API

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  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:2020-02-20, 11:08:47

最后更新:2020-02-20, 11:09:12

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

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