JDK8中新日期时间API

package day2_14;

import org.junit.Test;

import java.time.*;
import java.time.format.DateTimeFormatter;
import java.time.format.FormatStyle;
import java.time.temporal.TemporalAccessor;

/**
 * @Author Tianhao
 * @create 2021-02-14-21:47
 */
public class JDK8DateTimeTest {

    /*
    LocalDate、LocalTime、LocalDateTime 的使用
    说明：
         1.LocalDateTime用的多一些
         2.类似于Calendar
     */

    @Test
    public void test1() {
        //两种实例化方式

        //第一种：now():获取当前日期、时间、或者日期+时间来创建对象
        LocalDate localDate = LocalDate.now();
        LocalTime localTime = LocalTime.now();
        LocalDateTime localDateTime = LocalDateTime.now();
        System.out.println(localDate);//2021-02-14
        System.out.println(localTime);//22:11:01.820
        System.out.println(localDateTime);//2021-02-14T22:11:01.820

        //第二种：of():设置指定的年、月、日、时、分、秒。没有偏移量
        LocalDateTime localDateTime1 = LocalDateTime.of(2021, 2, 18, 13, 14, 59);
        System.out.println(localDateTime1);//2021-02-18T13:14:59

        System.out.println("**************");
        //getXxx()  获得相关的属性
        System.out.println(localDateTime.getDayOfMonth());
        System.out.println(localDateTime.getDayOfWeek()); //SUNDAY
        System.out.println(localDateTime.getDayOfYear());
        System.out.println(localDateTime.getMinute());
        System.out.println(localDateTime.getMonth());//FEBRUARY
        System.out.println(localDateTime.getMonthValue());//2

        System.out.println("****************");
        //下面都体现不可变性
        //withXxx()  设置相关的属性
        LocalDateTime localDateTime2 = localDateTime.withDayOfMonth(28);
        System.out.println(localDateTime);//2021-02-14T22:13:00.105
        System.out.println(localDateTime2);//2021-02-28T22:13:00.105

        LocalDateTime localDateTime3 = localDateTime.withHour(4);
        System.out.println(localDateTime);//2021-02-14T22:16:14.357
        System.out.println(localDateTime3);//2021-02-14T04:16:14.357

        System.out.println("****************");
        //增加相关属性值
        LocalDateTime localDateTime4 = localDateTime.plusMonths(3);
        System.out.println(localDateTime);//2021-02-14T22:19:52.258
        System.out.println(localDateTime4);//2021-05-14T22:19:52.258

        //减少相关属性值
        LocalDateTime localDateTime5 = localDateTime.minusDays(6);
        System.out.println(localDateTime);//2021-02-14T22:22:18.514
        System.out.println(localDateTime5);//2021-02-08T22:22:18.514
    }


    /*
        Instant:瞬时类
        类似于java.util.Date类
     */

    @Test
    public void test2() {
        //创建对象方式一：
        //now():获取本初子午线对应的标准时间
        Instant instant = Instant.now();
        System.out.println(instant);//2021-02-14T14:39:03.994Z

        //中国在东八区，时钟需要加上8小时的偏移量
        OffsetDateTime offsetDateTime = instant.atOffset(ZoneOffset.ofHours(8));
        System.out.println(offsetDateTime);//2021-02-14T22:39:03.994+08:00

        //toEpochMilli():获取自1970年1月1日0时0分0秒（UTC）开始的毫秒数
        //类似于Date类的getTime()
        long milli = instant.toEpochMilli();
        System.out.println(milli);//1613313872550

        System.out.println("***************");
        //创建对象方式二：
        //ofEpochMilli():通过给定的毫秒数获取一个Instant实例
        //类似于Date(Long millis)构造器
        Instant instant1 = Instant.ofEpochMilli(1613313872550L);
        System.out.println(instant1);//2021-02-14T14:44:32.550Z
    }

    /*
        DateTimeFormatter:格式化或解析日期、时间
        类似于SimpleDateFormat
         */
    @Test
    public void test3 () {

    //3种实例化方式
       //方式一：预定义的标准格式。如：ISO_LOCAL_DATE_TIME;ISO_LOCAL_DATE;ISO_LOCAL_TIME
        DateTimeFormatter formatter = DateTimeFormatter.ISO_LOCAL_DATE_TIME;
        LocalDateTime localDateTime = LocalDateTime.now();
        //格式化:日期--->字符串
        String str = formatter.format(localDateTime);
        System.out.println(localDateTime);//2021-02-15T13:08:53.245  --LocalDateTime类型
        System.out.println(str);//2021-02-15T13:08:53.245  --String类型

        //解析：字符串-->日期
        //TemporalAccessor接口,这里是多态
        TemporalAccessor parse = formatter.parse("2021-02-15T13:08:53.245");
        System.out.println(parse);//{},ISO resolved to 2021-02-15T13:08:53.245

        System.out.println("***************");
        //方式二：本地化相关的格式。如：ofLocalizedDateTime(FormatStyle.LONG)
        DateTimeFormatter formatter2 = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.LONG);
        String str2 = formatter2.format(localDateTime);
        System.out.println(str2);//2021年2月15日 下午01时21分21秒
        TemporalAccessor parse2 = formatter2.parse("2021年2月14日 下午03时59分59秒");
        System.out.println(parse2);//

        System.out.println("***************");
        //重点：方式三：自定义的格式，如：ofPattern("yyyy-MM-dd hh-mm-ss")
        DateTimeFormatter formatter3 = DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss");
        //格式化
        String str3 = formatter3.format(localDateTime);
        System.out.println(str3);//2021-02-15 01:36:11
        //解析
        TemporalAccessor parse3 = formatter3.parse("2021-02-15 02:59:59");
        System.out.println(parse3);
        //{NanoOfSecond=0, MicroOfSecond=0, HourOfAmPm=2, MinuteOfHour=59, MilliOfSecond=0, SecondOfMinute=59},ISO resolved to 2021-02-15


    }
}