JDK8中新日期时间API的复习

package day2_15;

import org.junit.Test;

import java.time.Instant;
import java.time.LocalDateTime;
import java.time.OffsetDateTime;
import java.time.ZoneOffset;
import java.time.format.DateTimeFormatter;
import java.time.temporal.TemporalAccessor;

/**
 * @Author Tianhao
 * @create 2021-02-14-20:53
 */
public class DateTimeTest {

    @Test
    public void testLocalDateTime() {
        //LocalDateTime  类似于Calendar
        //两种实例化方式
        //方式一：now()：当前日期时间
        LocalDateTime now = LocalDateTime.now();
        System.out.println(now);//2021-02-16T15:54:17.649
        //方式二：of():指定日期时间
        LocalDateTime past = LocalDateTime.of(2015, 6, 7, 11, 59, 59);
        System.out.println(past);//2015-06-07T11:59:59
        //获取相关属性
        System.out.println(now.getDayOfMonth());//16
        System.out.println(past.getMonthValue());//6

        System.out.println("**********");
        //对LocalDateTime操作(体现不变性)
        //设置相关属性，返回一个新的日期时间对象
        LocalDateTime now2 = now.withDayOfMonth(10);
        LocalDateTime past2 = past.withMonth(5);
        System.out.println(now2);//2021-02-10T16:02:34.914
        System.out.println(past2);//2015-05-07T11:59:59
        System.out.println(now.getDayOfMonth());//16
        System.out.println(past.getMonthValue());//6

        System.out.println("**********");
        //增加相关属性值，返回一个新的日期时间对象
        LocalDateTime now3 = now.plusDays(4);
        LocalDateTime past3 = past.plusMonths(3);
        System.out.println(now3);//2021-02-20T16:09:39.983
        System.out.println(past3);//2015-09-07T11:59:59
        System.out.println(now.getDayOfMonth());//16
        System.out.println(past.getMonthValue());//6

        System.out.println("**********");
        //减少相关属性值，返回一个新的日期时间对象
        LocalDateTime now4 = now.minusDays(8);
        LocalDateTime past4 = past.minusMonths(3);
        System.out.println(now4);//2021-02-08T16:13:43.328
        System.out.println(past4);//2015-03-07T11:59:59
        System.out.println(now.getDayOfMonth());//16
        System.out.println(past.getMonthValue());//6
    }

    @Test
    public void testInstant() {
        //两种实例化方式
        //方式一:本初子午线的标准时间
        Instant now = Instant.now();
        System.out.println(now);//2021-02-16T08:19:51.419Z
        //中国处于东八区，所以小时需要加上8小时的偏移量
        OffsetDateTime chinaNow = now.atOffset(ZoneOffset.ofHours(8));
        System.out.println(chinaNow);//2021-02-16T16:19:51.419+08:00

        //方式二：指定与1970年1月1日0时0秒0分的毫秒数差值来创建对象
        Instant now2 = Instant.ofEpochMilli(0);
        Instant now3 = Instant.ofEpochMilli(3600000L);
        System.out.println(now2);//1970-01-01T00:00:00Z
        System.out.println(now3);//1970-01-01T01:00:00Z

        //对Instant操作
        //获取当前时刻与1970年1月1日0时0秒0分的毫秒数差值
        long milli = now.toEpochMilli();
        System.out.println(milli);//1613464115414
    }

    @Test
    public void testDateTimeFormatter() {
        //有三种方式创建对象，这里只测常用的一种
        //自定义格式器
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss");
        //对DateTimeFormatter的操作
        //格式化  LocalDateTime -->String
        String str = formatter.format(LocalDateTime.now());
        System.out.println(str);//2021-02-16 04:39:21
        //解析  String--->LocalDateTime
        TemporalAccessor localDateTime = formatter.parse("2021-02-16 04:39:21");
        //{SecondOfMinute=21, NanoOfSecond=0, MicroOfSecond=0, MinuteOfHour=39, MilliOfSecond=0, HourOfAmPm=4},ISO resolved to 2021-02-16
        System.out.println(localDateTime);
    }

}