使用Java 8，引入了一个新的Date-Time API来弥补旧的日期时间API的以下缺点.
非线程安全 : java.util.Date不是线程安全的，因此开发人员必须在使用date时处理并发问题.新的日期时间API是不可变的，并且没有setter方法.
设计不佳 : 默认日期从1900开始，月从1开始，日从0开始，因此没有统一性.旧API具有较少的日期操作直接方法.新API为此类操作提供了许多实用方法.
困难的时区处理 : 开发人员必须编写大量代码来处理时区问题.新API的开发考虑了特定于域的设计.
Java 8在java包下引入了一个新的日期时间API .时间.以下是java.time包中引入的一些重要类.
Local : 简化了日期时间API，没有时区处理的复杂性.
Zoned : 用于处理各种时区的专用日期时间API.
LocalDate/LocalTime和LocalDateTime类简化了不需要时区的开发.让我们看看它们的实际效果.
使用您选择的任何编辑器创建以下java程序，例如C:\> 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 = 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);
}
}使用 javac编译班级编译如下 :
C:\JAVA>javac Java8Tester.java
现在运行Java8Tester如下 :
C:\JAVA>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
在考虑时区时使用分区日期时间API.让我们看看它们的运行情况.
使用您选择的任何编辑器创建以下Java程序，例如C:\> JAVA.
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);
}
}使用 javac编译班级编译如下 :
C:\ JAVA> javac Java8Tester.java
现在运行Java8Tester如下 :
C:\ JAVA> 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
在Java 8中添加了java.time.temporal.ChronoUnit枚举，以替换旧API中用于表示日，月等的整数值.让我们看看它们的运行情况.
使用您选择的任何编辑器创建以下Java程序，例如C:\> JAVA.
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);
}
}使用 javac编译班级编译如下 :
C:\JAVA>javac Java8Tester.java
现在运行Java8Tester如下 :
C:\JAVA>java Java8Tester
它应该产生以下结果 :
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
使用Java 8时，会引入两个专门的类来处理时差.
期间 : 它处理基于日期的时间量.
持续时间 : 它处理基于时间的时间量.
让我们看看它们的运作情况.
使用您选择的任何编辑器创建以下Java程序，例如C:\> 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 = 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);
}
}使用 javac编译班级编译如下 :
C:\JAVA>javac Java8Tester.java
现在运行Java8Tester如下 :
C:\JAVA>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
TemporalAdjuster用于执行日期数学.例如，获取"本月第二个星期六"或"下周二".让我们看看它们的运行情况.
使用您选择的任何编辑器创建以下Java程序，例如C:\> 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 = 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);
}
}使用 javac编译班级编译如下 :
C:\JAVA>javac Java8Tester.java
现在运行Java8Tester如下 :
C:\JAVA>java Java8Tester
它应该产生以下结果 :
Current date: 2014-12-10 Next Tuesday on : 2014-12-16 Second Saturday on : 2014-12-13
一个toInstant()方法被添加到原始的Date和Calendar对象中，可用于将它们转换为新的Date-Time API.使用ofInstant(Insant，ZoneId)方法获取LocalDateTime或ZonedDateTime对象.让我们看看它们的运行情况.
使用您选择的任何编辑器创建以下Java程序，例如C:\> 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 = 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);
}
}使用 javac编译班级编译如下 :
C:\JAVA>javac Java8Tester.java
现在运行Java8Tester如下 :
C:\JAVA>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]
