java8中新的Date和Time详解

新Date类和Time类背后的设计原则：

不可变类

java8之前，Date类都是可变类。当我们在多线程环境下使用它，编程人员应该确认Date对象的线程安全。Java8的Date和Time API提供了线程安全的不可变类。编程人员不用考虑并发的问题。

领域模型驱动设计方法

新的日期和时间的类别遵循“域驱动设计”。对于开发者来说，理解方法和类的功能是很容易的。

接下来让我们来看看新Date和Time API:

1.java.time.LocalDate:

LocalDate只提供日期不提供时间信息。它是不可变类且线程安全的。

package org.smarttechie;
import java.time.LocalDate;
import java.time.temporal.ChronoUnit;
/**
* This class demonstrates JAVA 8 data and time API
* @author Siva Prasad Rao Janapati
* */
public class DateTimeDemonstration {
/**
* @param args
*/
public static void main(String[] args) {
  //Create date LocalDate localDate = LocalDate.now();
  System.out.println("The local date is :: " + localDate); 
  //Find the length of the month. That is, how many days are there for this month.
  System.out.println("The number of days available for this month:: " + localDate.lengthOfMonth()); 
  //Know the month name
  System.out.println("What is the month name? :: " + localDate.getMonth().name()); 
  //add 2 days to the today's date.
  System.out.println(localDate.plus(2, ChronoUnit.DAYS)); 
  //substract 2 days from today
  System.out.println(localDate.minus(2, ChronoUnit.DAYS)); 
  //Convert the string to date
  System.out.println(localDate.parse("2017-04-07"));
 }
}

2.java.time.LocalTime:

LocalTime只提供时间而不提供日期信息，它是不可变类且线程安全的。

package org.smarttechie;
import java.time.LocalTime;
import java.time.temporal.ChronoUnit;
/**
* This class demonstrates JAVA 8 data and time API
* @author Siva Prasad Rao Janapati
* */
public class DateTimeDemonstration {
/**
* @param args
*/
public static void main(String[] args) {
  //Get local time
  LocalTime localTime = LocalTime.now();
  System.out.println(localTime);
 //Get the hour of the day
 System.out.println("The hour of the day:: " + localTime.getHour());
 //add 2 hours to the time.
 System.out.println(localTime.plus(2, ChronoUnit.HOURS));
 //add 6 minutes to the time.
 System.out.println(localTime.plusMinutes(6));
 //substract 2 hours from current time
 System.out.println(localTime.minus(2, ChronoUnit.HOURS));
 }
}

3.java.time.LocalDateTime:

LocalDateTime提供时间和日期的信息，它是不可变类且线程安全的

package orr.smarttechie;
import java.time.LocalDateTime;
import java.time.temporal.ChronoUnit;
/**
* This class demonstrates JAVA 8 data and time API
* @author Siva Prasad Rao Janapati
*
*/
public class DateTimeDemonstration {
/**
* @param args
*/
public static void main(String[] args) {
  //Get LocalDateTime object
  LocalDateTime localDateTime = LocalDateTime.now();
  System.out.println(localDateTime);
  //Find the length of month. That is, how many days are there for this month.
  System.out.println("The number of days available for this month:: " + localDateTime.getMonth().length(true));
  //Know the month name
  System.out.println("What is the month name? :: " + localDateTime.getMonth().name());
  //add 2 days to today's date.
  System.out.println(localDateTime.plus(2, ChronoUnit.DAYS));
  //substract 2 days from today
  System.out.println(localDateTime.minus(2, ChronoUnit.DAYS));
 }
}

4.java.time.Year:

 Year提供年的信息，它是不可变类且线程安全的。

package orr.smarttechie;
import java.time.Year;
import java.time.temporal.ChronoUnit;
/**
* This class demonstrates JAVA 8 data and time API
* @author Siva Prasad Rao Janapati
*
*/
public class DateTimeDemonstration {
/**
* @param args
*/
public static void main(String[] args) {
  //Get year
  Year year = Year.now();
  System.out.println("Year ::" + year);
  //know the year is leap year or not
  System.out.println("Is year[" +year+"] leap year?"+ year.isLeap());
 }
}

 5.java.time.Duration:

Duration是用来计算两个给定的日期之间包含多少秒，多少毫秒，它是不可变类且线程安全的

6.java.time.Period:

Period是用来计算两个给定的日期之间包含多少天，多少月或者多少年，它是不可变类且线程安全的

package orr.smarttechie;
import java.time.LocalDate;
import java.time.Period;
import java.time.temporal.ChronoUnit;
/**
* This class demonstrates JAVA 8 data and time API
* @author Siva Prasad Rao Janapati
*
*/
public class DateTimeDemonstration {
/**
* @param args
*/
public static void main(String[] args) {
  LocalDate localDate = LocalDate.now();
  Period period = Period.between(localDate, localDate.plus(2, ChronoUnit.DAYS));
  System.out.println(period.getDays());
 }
}