JDK8日期、时间的使用

 1 import org.junit.Test;

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;

/**
 * LocalDate,LocalTime,LocalDateTime的使用
 * @author fu jingchao
 * @creat 2021/12/2-17:22
 */
public class JDK8DateTimeTest {
    @Test
    public void test1(){
        //now():获取当前的日期、时间、日期+时间
        LocalDate localDate = LocalDate.now();
        LocalTime localTime = LocalTime.now();
        LocalDateTime localDateTime = LocalDateTime.now();
        System.out.println(localDate);//2021-12-02
        System.out.println(localTime);//17:43:43.962
        System.out.println(localDateTime);//2021-12-02T17:43:43.962

        //getXxx():获取相关的属性
        System.out.println(localDateTime.getDayOfMonth());
        System.out.println(localDateTime.getDayOfWeek());
        System.out.println(localDateTime.getMonth());

        //of:指定时间创建对象
        LocalDateTime localDateTime1 = LocalDateTime.of(2021,12,2,17,
                50,28);
        System.out.println(localDateTime1);//2021-12-02T17:50:28

        //体现不可变性
        //withXxx():设置相关的属性
        LocalDate localDate1 = localDate.withDayOfMonth(22);
        System.out.println(localDate);//2021-12-02
        System.out.println(localDate1);//2021-12-22

        LocalDateTime localDateTime2 = localDateTime.withHour(4);//相当于设置成4点
        System.out.println(localDateTime);//2021-12-03T14:09:37.680
        System.out.println(localDateTime2);//2021-12-03T04:09:37.680

        //加
        LocalDateTime localDateTime3 = localDateTime.plusMonths(3);
        System.out.println(localDateTime);//2021-12-03T14:09:37.680
        System.out.println(localDateTime3);//2022-03-03T14:09:37.680

        //减
        LocalDateTime localDateTime4 = localDateTime.minusDays(3);
        System.out.println(localDateTime);//2021-12-03T14:13:03.345
        System.out.println(localDateTime4);//2021-11-30T14:13:03.345
    }
}

 

   /*
   Instant的使用
    类似于java.util.Date类

    */
    @Test
    public void test2(){
        //now()获取本初子午线对应的标准时间
        Instant instant = Instant.now();
        System.out.println(instant);//2021-12-03T07:36:54.266Z

        //东八区(北京时间)
        OffsetDateTime offsetDateTime = instant.atOffset(ZoneOffset.ofHours(8));
        System.out.println(offsetDateTime);//2021-12-03T15:36:54.266+08:00

        //获取自1970年1月1日0时0分0秒（UTC）开始的毫秒数---->Date类的getTime()
        long mill = instant.toEpochMilli();
        System.out.println(mill);//1638517411713

        //ofEpochMilli():通过指定的毫秒数，获取Instant实例------>Date(long millis)
        Instant instant1 = Instant.ofEpochMilli(1638517411713L);
        System.out.println(instant1);//2021-12-03T07:43:31.713Z

    }

 

    /*
    DateTimeFormatter:格式化或解析日期、时间
        类似于SimpleDateFormat
     */
    @Test
    public void test3(){
        //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 str1 = formatter.format(localDateTime);
        System.out.println(localDateTime);//2021-12-03T16:14:16.243
        System.out.println(str1);//2021-12-03T16:14:16.243
        System.out.println(localDateTime.getClass());//class java.time.LocalDateTime
        System.out.println(str1.getClass());//class java.lang.String

        //解析：字符串---->日期
        TemporalAccessor parse = formatter.parse("2021-12-03T16:14:16.243");
        System.out.println(parse);//{},ISO resolved to 2021-12-03T16:14:16.243

        //方式二：本地化相关的格式。如：ofLocalizedDateTime(FormatStyle.LONG)
        //FormatStyle.LONG/ FormatStyle.MEDIUM/ FormatStyle.SHORT:适用于LocalDateTime
        DateTimeFormatter formatter1 = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.SHORT);
        DateTimeFormatter formatter2 = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.LONG);
        //格式化
        String str2 = formatter1.format(localDateTime);
        System.out.println(str2);//21-12-3 下午4:30

        String str3 = formatter2.format(localDateTime);
        System.out.println(str3);//2021年12月3日 下午04时30分39秒

        //本地化相关的格式。如：ofLocalizedDate()
        //FormatStyle.FULL/ FormatStyle.LONG/ FormatStyle.MEDIUM/ FormatStyle.SHORT:适用于LocalDate
        DateTimeFormatter formatter3 = DateTimeFormatter.ofLocalizedDate(FormatStyle.FULL);
        //格式化
        String str4 = formatter3.format(LocalDate.now());
        System.out.println(str4);//2021年12月3日 星期五

        DateTimeFormatter formatter4 = DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM);
        //格式化
        String str5 = formatter4.format(LocalDate.now());
        System.out.println(str5);//2021-12-3

        //方式三：自定义的格式：如：ofPattern("yyyy-MM-dd hh:mm:ss E")
        DateTimeFormatter formatter5 = DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss");
        //格式化
        String str6 = formatter5.format(LocalDateTime.now());
        System.out.println(str6);//2021-12-03 04:44:10

        //解析
        TemporalAccessor parse1 = formatter5.parse("2021-12-03 04:44:10");
        System.out.println(parse1);//{NanoOfSecond=0, MilliOfSecond=0, MinuteOfHour=44, HourOfAmPm=4, SecondOfMinute=10, MicroOfSecond=0},ISO resolved to 2021-12-03


    }