newdatejava_Java8NewDate/TimeAPI

Java 8 - New Date/Time API

使用Java 8&＃xff0c;引入了一个新的Date-Time API来解决旧的日期时间API的以下缺点 -

线程不安全 - java.util.Date不是线程安全的&＃xff0c;因此开发人员必须在使用日期时处理并发问题。新的日期时间API是不可变的&＃xff0c;没有setter方法。

设计差 - 默认日期从1900开始&＃xff0c;月份从1开始&＃xff0c;日期从0开始&＃xff0c;所以没有一致性。旧的API对日期操作的方法较少。新的API为此类操作提供了许多实用方法。

困难的时区处理 - 开发人员不得不编写大量代码来处理时区问题。新的API已经开发出了保持领域特定的设计。

Java 8在java.time包下引入了一个新的日期时间API 。以下是java.time包中介绍的一些重要类 -

本地 - 简化的日期时间API&＃xff0c;没有时区处理的复杂性。

分区 - 处理各种时区的专用日期API。

本地日期时间API

LocalDate / LocalTime和LocalDateTime类简化了不需要时区的开发。让我们看看他们在行动 -

Java8Tester.java

import java.time.LocalDate;

import java.time.LocalTime;

import java.time.LocalDateTime;

import java.time.Month;

public class Java8Tester {

public static void main(String args[]){

Java8Tester java8tester &＃61; new Java8Tester();

java8tester.testLocalDateTime();

}

public void testLocalDateTime(){

// Get the current date and time

LocalDateTime currentTime &＃61; LocalDateTime.now();

System.out.println("Current DateTime: " &＃43; currentTime);

LocalDate date1 &＃61; currentTime.toLocalDate();

System.out.println("date1: " &＃43; date1);

Month month &＃61; currentTime.getMonth();

int day &＃61; currentTime.getDayOfMonth();

int seconds &＃61; currentTime.getSecond();

System.out.println("Month: " &＃43; month &＃43;"day: " &＃43; day &＃43;"seconds: " &＃43; seconds);

LocalDateTime date2 &＃61; currentTime.withDayOfMonth(10).withYear(2012);

System.out.println("date2: " &＃43; date2);

//12 december 2014

LocalDate date3 &＃61; LocalDate.of(2014, Month.DECEMBER, 12);

System.out.println("date3: " &＃43; date3);

//22 hour 15 minutes

LocalTime date4 &＃61; LocalTime.of(22, 15);

System.out.println("date4: " &＃43; date4);

//parse a string

LocalTime date5 &＃61; LocalTime.parse("20:15:30");

System.out.println("date5: " &＃43; date5);

}

}

验证结果

使用javac编译器编译类&＃xff0c;如下所示&＃xff1a;

$javac Java8Tester.java

现在运行Java8Tester如下 -

$java Java8Tester

它应该产生以下输出 -

Current DateTime: 2014-12-09T11:00:45.457

date1: 2014-12-09

Month: DECEMBERday: 9seconds: 45

date2: 2012-12-10T11:00:45.457

date3: 2014-12-12

date4: 22:15

date5: 20:15:30

分区日期时间API

在考虑时区时使用分区日期时间API。让我们看看他们在行动 -

Java8Tester.java

import java.time.ZonedDateTime;

import java.time.ZoneId;

public class Java8Tester {

public static void main(String args[]){

Java8Tester java8tester &＃61; new Java8Tester();

java8tester.testZonedDateTime();

}

public void testZonedDateTime(){

// Get the current date and time

ZonedDateTime date1 &＃61; ZonedDateTime.parse("2007-12-03T10:15:30&＃43;05:30[Asia/Karachi]");

System.out.println("date1: " &＃43; date1);

ZoneId id &＃61; ZoneId.of("Europe/Paris");

System.out.println("ZoneId: " &＃43; id);

ZoneId currentZone &＃61; ZoneId.systemDefault();

System.out.println("CurrentZone: " &＃43; currentZone);

}

}

验证结果

使用javac编译器编译类&＃xff0c;如下所示&＃xff1a;

$javac Java8Tester.java

现在运行Java8Tester如下 -

$java Java8Tester

它应该产生以下输出 -

date1: 2007-12-03T10:15:30&＃43;05:00[Asia/Karachi]

ZoneId: Europe/Paris

CurrentZone: Etc/UTC

计时单位枚举

java.time.temporal.ChronoUnit枚举在Java 8中添加&＃xff0c;以替换旧API中使用的整数值来表示日&＃xff0c;月等。让我们看看它们在行动中 -

Java8Tester.java

import java.time.LocalDate;

import java.time.temporal.ChronoUnit;

public class Java8Tester {

public static void main(String args[]){

Java8Tester java8tester &＃61; new Java8Tester();

java8tester.testChromoUnits();

}

public void testChromoUnits(){

//Get the current date

LocalDate today &＃61; LocalDate.now();

System.out.println("Current date: " &＃43; today);

//add 1 week to the current date

LocalDate nextWeek &＃61; today.plus(1, ChronoUnit.WEEKS);

System.out.println("Next week: " &＃43; nextWeek);

//add 1 month to the current date

LocalDate nextMonth &＃61; today.plus(1, ChronoUnit.MONTHS);

System.out.println("Next month: " &＃43; nextMonth);

//add 1 year to the current date

LocalDate nextYear &＃61; today.plus(1, ChronoUnit.YEARS);

System.out.println("Next year: " &＃43; nextYear);

//add 10 years to the current date

LocalDate nextDecade &＃61; today.plus(1, ChronoUnit.DECADES);

System.out.println("Date after ten year: " &＃43; nextDecade);

}

}

验证结果

使用javac编译器编译类&＃xff0c;如下所示&＃xff1a;

$javac Java8Tester.java

现在运行Java8Tester如下 -

$java Java8Tester

应该产生以下结果 -

Current date: 2014-12-10

Next week: 2014-12-17

Next month: 2015-01-10

Next year: 2015-12-10

Date after ten year: 2024-12-10

期间与期限

使用Java 8&＃xff0c;引入了两个专门的课程来处理时间差异 -

期间 - 它处理基于日期的时间量。

持续时间 - 它处理时间的时间量

。

让我们以一个例子来理解他们 -

Java8Tester.java

import java.time.temporal.ChronoUnit;

import java.time.LocalDate;

import java.time.LocalTime;

import java.time.Duration;

import java.time.Period;

public class Java8Tester {

public static void main(String args[]){

Java8Tester java8tester &＃61; new Java8Tester();

java8tester.testPeriod();

java8tester.testDuration();

}

public void testPeriod(){

//Get the current date

LocalDate date1 &＃61; LocalDate.now();

System.out.println("Current date: " &＃43; date1);

//add 1 month to the current date

LocalDate date2 &＃61; date1.plus(1, ChronoUnit.MONTHS);

System.out.println("Next month: " &＃43; date2);

Period period &＃61; Period.between(date2, date1);

System.out.println("Period: " &＃43; period);

}

public void testDuration(){

LocalTime time1 &＃61; LocalTime.now();

Duration twoHours &＃61; Duration.ofHours(2);

LocalTime time2 &＃61; time1.plus(twoHours);

Duration duration &＃61; Duration.between(time1, time2);

System.out.println("Duration: " &＃43; duration);

}

}

验证结果

使用javac编译器编译类&＃xff0c;如下所示&＃xff1a;

$javac Java8Tester.java

现在运行Java8Tester如下 -

$java Java8Tester

它应该产生以下输出 -

Current date: 2014-12-10

Next month: 2015-01-10

Period: P-1M

Duration: PT2H

时间调整器

TemporalAdjuster用于执行日期数学。例如&＃xff0c;获得“本月第二个星期六”或“下周二”。让我们看一个例子 -

Java8Tester.java

import java.time.LocalDate;

import java.time.temporal.TemporalAdjusters;

import java.time.DayOfWeek;

public class Java8Tester {

public static void main(String args[]){

Java8Tester java8tester &＃61; new Java8Tester();

java8tester.testAdjusters();

}

public void testAdjusters(){

//Get the current date

LocalDate date1 &＃61; LocalDate.now();

System.out.println("Current date: " &＃43; date1);

//get the next tuesday

LocalDate nextTuesday &＃61; date1.with(TemporalAdjusters.next(DayOfWeek.TUESDAY));

System.out.println("Next Tuesday on : " &＃43; nextTuesday);

//get the second saturday of next month

LocalDate firstInYear &＃61; LocalDate.of(date1.getYear(),date1.getMonth(), 1);

LocalDate secondSaturday &＃61; firstInYear.with(TemporalAdjusters.nextOrSame(DayOfWeek.SATURDAY)).with(TemporalAdjusters.next(DayOfWeek.SATURDAY));

System.out.println("Second Saturday on : " &＃43; secondSaturday);

}

}

验证结果

使用javac编译器编译类&＃xff0c;如下所示&＃xff1a;

$javac Java8Tester.java

现在运行Java8Tester如下 -

$java Java8Tester

应该产生以下结果 -

Current date: 2014-12-10

Next Tuesday on : 2014-12-16

Second Saturday on : 2014-12-13

向后兼容性

将一个toInstant()方法添加到原始的Date和Calendar对象中&＃xff0c;可以将它们转换为新的Date-Time API。使用一个Instant(Insant&＃xff0c;ZoneId)方法来获取一个LocalDateTime或ZonedDateTime对象。让我们以一个例子来理解它 -

Java8Tester.java

import java.time.LocalDateTime;

import java.time.ZonedDateTime;

import java.util.Date;

import java.time.Instant;

import java.time.ZoneId;

public class Java8Tester {

public static void main(String args[]){

Java8Tester java8tester &＃61; new Java8Tester();

java8tester.testBackwardCompatability();

}

public void testBackwardCompatability(){

//Get the current date

Date currentDate &＃61; new Date();

System.out.println("Current date: " &＃43; currentDate);

//Get the instant of current date in terms of milliseconds

Instant now &＃61; currentDate.toInstant();

ZoneId currentZone &＃61; ZoneId.systemDefault();

LocalDateTime localDateTime &＃61; LocalDateTime.ofInstant(now, currentZone);

System.out.println("Local date: " &＃43; localDateTime);

ZonedDateTime zonedDateTime &＃61; ZonedDateTime.ofInstant(now, currentZone);

System.out.println("Zoned date: " &＃43; zonedDateTime);

}

}

验证结果

使用javac编译器编译类&＃xff0c;如下所示&＃xff1a;

$javac Java8Tester.java

现在运行Java8Tester如下 -

$java Java8Tester

它应该产生以下输出 -

Current date: Wed Dec 10 05:44:06 UTC 2014

Local date: 2014-12-10T05:44:06.635

Zoned date: 2014-12-10T05:44:06.635Z[Etc/UTC]