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

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