Java 8 - New Date/Time API

使用Java 8,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,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,没有setter方法。
  • 设计差 - 默认日期从1900开始,月份从1开始,日期从0开始,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,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

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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 = new Java8Tester();
java8tester.testLocalDateTime();
}
public void testLocalDateTime(){
// Get the current date and time
LocalDateTime currentTime = LocalDateTime.now();
System.out.println("Current DateTime: " + 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("Month: " + month +"day: " + day +"seconds: " + seconds);
LocalDateTime date2 = currentTime.withDayOfMonth(10).withYear(2012);
System.out.println("date2: " + date2);
//12 december 2014
LocalDate date3 = LocalDate.of(2014, Month.DECEMBER, 12);
System.out.println("date3: " + date3);
//22 hour 15 minutes
LocalTime date4 = LocalTime.of(22, 15);
System.out.println("date4: " + date4);
//parse a string
LocalTime date5 = LocalTime.parse("20:15:30");
System.out.println("date5: " + date5);
}
}

验证结果
使用javac编译器编译类,如下所示:

$javac Java8Tester.java

现在运行Java8Tester如下 -

$java Java8Tester

它应该产生以下输出 -

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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

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import java.time.ZonedDateTime;
import java.time.ZoneId;
public class Java8Tester {
public static void main(String args[]){
Java8Tester java8tester = new Java8Tester();
java8tester.testZonedDateTime();
}
public void testZonedDateTime(){
// Get the current date and time
ZonedDateTime date1 = ZonedDateTime.parse("2007-12-03T10:15:30+05:30[Asia/Karachi]");
System.out.println("date1: " + date1);
ZoneId id = ZoneId.of("Europe/Paris");
System.out.println("ZoneId: " + id);
ZoneId currentZone = ZoneId.systemDefault();
System.out.println("CurrentZone: " + currentZone);
}
}

验证结果
使用javac编译器编译类,如下所示:

$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+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,以替换旧API中使用的整数值来表示日,月等。让我们看看它们在行动中 -

Java8Tester.java

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import java.time.LocalDate;
import java.time.temporal.ChronoUnit;
public class Java8Tester {
public static void main(String args[]){
Java8Tester java8tester = new Java8Tester();
java8tester.testChromoUnits();
}
public void testChromoUnits(){
//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);
}
}

验证结果
使用javac编译器编译类,如下所示:

$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,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

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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 = new Java8Tester();
java8tester.testPeriod();
java8tester.testDuration();
}
public void 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);
}
public void 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);
}
}

验证结果
使用javac编译器编译类,如下所示:

$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,获得“本月第二个星期六”或“下周二”。让我们看一个例子 -

Java8Tester.java

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import java.time.LocalDate;
import java.time.temporal.TemporalAdjusters;
import java.time.DayOfWeek;
public class Java8Tester {
public static void main(String args[]){
Java8Tester java8tester = new Java8Tester();
java8tester.testAdjusters();
}
public void testAdjusters(){
//Get the current date
LocalDate date1 = LocalDate.now();
System.out.println("Current date: " + date1);
//get the next tuesday
LocalDate nextTuesday = date1.with(TemporalAdjusters.next(DayOfWeek.TUESDAY));
System.out.println("Next Tuesday on : " + nextTuesday);
//get the second saturday of next month
LocalDate firstInYear = LocalDate.of(date1.getYear(),date1.getMonth(), 1);
LocalDate secondSaturday = firstInYear.with(TemporalAdjusters.nextOrSame(DayOfWeek.SATURDAY)).with(TemporalAdjusters.next(DayOfWeek.SATURDAY));
System.out.println("Second Saturday on : " + secondSaturday);
}
}

验证结果
使用javac编译器编译类,如下所示:

$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,可以将它们转换为新的Date-Time API。使用一个Instant(Insant,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

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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 = new Java8Tester();
java8tester.testBackwardCompatability();
}
public void 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);
}
}

验证结果
使用javac编译器编译类,如下所示:

$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]