New Date API介绍

一、新的Date API介绍

LocalDate
LocalTime
Instant
Duration
Period

formatter
parsejdk以前的java.util.Date存在的问题

1）比如new Date(119, 2, 18)表示Mon Mar 18 00:00:00 CST 2019，2019年3月18日，year要从1900年加起，month是从0开始，day是从1开始。

2）SimpleDateFormat不是线程安全的，比如多线程情况下simpleDateFormat.parse会出问题。

3）Date名字叫日期，但是后面还有time时间

例子如下：

 package com.cy.java8;

 import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.util.Date;

 public class DateTest {

     public static void main(String[] args) throws ParseException {
         Date date = new Date(119, 2, 18);
         System.out.println(date);

         SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
         for(int i=0; i<5; i++){
             new Thread(()->{
                 try {
                     Date parseDate = sdf.parse("20190505");
                     System.out.println(parseDate);
                 } catch (ParseException e) {
                     e.printStackTrace();
                 }

             }).start();
         }
     }
 }

二、LocalDate　　　　　　

 package com.cy.java8;

 import java.time.LocalDate;
 import java.time.temporal.ChronoField;

 public class DateTest {

     public static void main(String[] args) {
         testLocalDate();
     }

     /**
      * LocalDate是线程安全的
      */
     private static void testLocalDate(){
         LocalDate localDate = LocalDate.of(2019, 10, 2);
         System.out.println(localDate.getYear());
         System.out.println(localDate.getMonth());
         System.out.println(localDate.getMonthValue());
         System.out.println(localDate.getDayOfYear());
         System.out.println(localDate.getDayOfMonth());
         System.out.println(localDate.getDayOfWeek());

         System.out.println(localDate.get(ChronoField.YEAR));
         System.out.println(localDate.get(ChronoField.MONTH_OF_YEAR));
         System.out.println(localDate.get(ChronoField.DAY_OF_MONTH));

         LocalDate now = LocalDate.now();
         System.out.println(now);
     }
 }

console：

2019
OCTOBER
10
275
2
WEDNESDAY
2019
10
2
2019-10-02

三、LocalTime、Instant、Duration、Period简单介绍

 package com.cy.java8;

 import java.time.*;

 public class DateTest {

     public static void main(String[] args) throws InterruptedException {
         testLocalTime();
         System.out.println("=================================");

         testCombineLocalDateAndTime();
         System.out.println("=================================");

         testInstant();
         System.out.println("=================================");

         testDuration();
         System.out.println("=================================");

         testPeriod();
     }

     private static void testLocalTime(){
         LocalTime time = LocalTime.now();
         System.out.println(time);

         System.out.println(time.getHour());
         System.out.println(time.getMinute());
         System.out.println(time.getSecond());
     }

     private static void testCombineLocalDateAndTime(){
         LocalDate localDate = LocalDate.now();
         LocalTime time = LocalTime.now();
         LocalDateTime localDateTime = LocalDateTime.of(localDate, time);
         System.out.println(localDateTime);

         LocalDateTime now = LocalDateTime.now();
         System.out.println(now);
     }

     private static void testInstant() throws InterruptedException {
         Instant start = Instant.now();
         Thread.sleep(1000);
         Instant end = Instant.now();

         Duration duration = Duration.between(start, end);   //类似于之前的System.currentTimeMillis
         System.out.println(duration.toMillis());
     }

     private static void testDuration(){
         LocalTime time = LocalTime.now();
         LocalTime beforeTime = time.minusHours(1);
         Duration duration = Duration.between(time, beforeTime);
         System.out.println(duration.toHours());
     }

     private static void testPeriod(){
         Period period = Period.between(LocalDate.of(2017, 9, 1), LocalDate.of(2019, 10, 2));
         System.out.println(period.getYears());
         System.out.println(period.getMonths());
         System.out.println(period.getDays());
     }
 }

console：

21:03:28.136
21
3
28
=================================
2019-10-02T21:03:28.137
2019-10-02T21:03:28.137
=================================
1001
=================================
-1
=================================
2
1
1

　　

四、formatter、parse

 package com.cy.java8;

 import java.time.*;
 import java.time.format.DateTimeFormatter;

 public class DateTest {

     public static void main(String[] args){
         testDateFormat();
         System.out.println("==============================");

         testDateParse();
     }

     private static void testDateFormat(){
         LocalDate localDate = LocalDate.now();
         String format1 = localDate.format(DateTimeFormatter.BASIC_ISO_DATE);
         System.out.println(format1);

         String format2 = localDate.format(DateTimeFormatter.ISO_LOCAL_DATE);
         System.out.println(format2);

         DateTimeFormatter myFormatter = DateTimeFormatter.ofPattern("yyyy年MM月dd日");
         String format3 = localDate.format(myFormatter);
         System.out.println(format3);
     }

     private static void testDateParse(){
         String date0 = "20191002";
         LocalDate localDate0 = LocalDate.parse(date0, DateTimeFormatter.BASIC_ISO_DATE);
         System.out.println(localDate0);

         String date1 = "2019-10-02";
         LocalDate localDate1 = LocalDate.parse(date1, DateTimeFormatter.ISO_LOCAL_DATE);
         System.out.println(localDate1);

         String date2 = "2019年10月02日";
         LocalDate localDate2 = LocalDate.parse(date2, DateTimeFormatter.ofPattern("yyyy年MM月dd日"));
         System.out.println(localDate2);
     }
 }

console：

20191002
2019-10-02
2019年10月02日
==============================
2019-10-02
2019-10-02
2019-10-02

----