Java8新特性——新一套日期时间API

文章目录：

1.新旧对比（线程安全问题）

2.LocalDate

3.LocalTime

4.LocalDateTime

5.Instant

6.Duration、Period

7.TestTemporalAdjuster、TestTemporalAdjusters

8.DateTimeFormatter

1.新旧对比（线程安全问题）

我们先来看下面的代码： （关于代码中某些类中的某些方法，我在这里就不说了，大家可以去查找api文档）

package com.szh.java8.datetime;

import java.text.SimpleDateFormat;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.concurrent.*;


public class TestSimpleDateFormat {

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");

        Callable task1 = new Callable() {
            @Override
            public Date call() throws Exception {
                return sdf.parse("20211109");
            }
        };

        ExecutorService pool1 = Executors.newFixedThreadPool(10);
        List> futureList1 = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            futureList1.add(pool1.submit(task1));
        }

        for (Future future : futureList1) {
            System.out.println(future.get());
        }

        pool1.shutdown();

        //=================================================================

//        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyyMMdd");
//
//        Callable task2 = new Callable() {
//            @Override
//            public LocalDate call() throws Exception {
//                return LocalDate.parse("20211109",dtf);
//            }
//        };
//
//        ExecutorService pool2 = Executors.newFixedThreadPool(10);
//        List> futureList2 = new ArrayList<>();
//        for (int i = 0; i < 10; i++) {
//            futureList2.add(pool2.submit(task2));
//        }
//
//        for (Future future : futureList2) {
//            System.out.println(future.get());
//        }
//
//        pool2.shutdown();
    }
}

运行之后，就出现了线程安全问题。

将代码中的上半部分注释掉，然后打开下半部分的代码，再次运行，线程安全问题就不存在了。

也就是Java8中提供了新一套日期时间API已经解决了线程安全问题。

2.LocalDate

package com.szh.java8.datetime;

import java.time.LocalDate;


public class TestLocalDate {

    public static void main(String[] args) {
        LocalDate ld1 = LocalDate.now();
        System.out.println(ld1);

        LocalDate ld2 = LocalDate.of(2021,5,1);
        System.out.println(ld2);

        LocalDate ld3 = ld1.plusYears(20);
        System.out.println(ld3);

        LocalDate ld4 = ld1.minusMonths(3);
        System.out.println(ld4);

        System.out.println(ld1.isBefore(ld2));
        System.out.println(ld2.isAfter(ld1));
        System.out.println(ld1.isLeapYear());

        System.out.println("年：" + ld1.getYear() + ", 月：" + ld1.getMonth() + ", 日：" + ld1.getDayOfMonth());
        System.out.println("年：" + ld1.getYear() + ", 月：" + ld1.getMonthValue() + ", 日：" + ld1.getDayOfMonth());
    }
}

3.LocalTime

package com.szh.java8.datetime;

import java.time.LocalTime;


public class TestLocalTime {

    public static void main(String[] args) {
        LocalTime lt1 = LocalTime.now();
        System.out.println(lt1);

        LocalTime lt2 = LocalTime.of(13,14,15);
        System.out.println(lt2);

        LocalTime lt3 = lt2.plusHours(3);
        System.out.println(lt3);

        LocalTime lt4 = lt2.minusMinutes(14);
        System.out.println(lt4);

        System.out.println(lt1.isBefore(lt2));
        System.out.println(lt2.isAfter(lt1));
        System.out.println("小时：" + lt1.getHour() + ", 分钟：" + lt1.getMinute() + ", 秒：" + lt1.getSecond());
    }
}

4.LocalDateTime

package com.szh.java8.datetime;

import java.time.LocalDateTime;


public class TestLocalDateTime {

    public static void main(String[] args) {
        LocalDateTime ldt1 = LocalDateTime.now();
        System.out.println(ldt1);

        LocalDateTime ldt2 = LocalDateTime.of(2020,5,1,13,14,15);
        System.out.println(ldt2);

        LocalDateTime ldt3 = ldt1.plusYears(15);
        System.out.println(ldt3);

        LocalDateTime ldt4 = ldt1.minusDays(20);
        System.out.println(ldt4);

        System.out.println(ldt1.isBefore(ldt2));
        System.out.println(ldt2.isAfter(ldt1));
        System.out.println("年：" + ldt2.getYear() + ", 月：" + ldt2.getMonthValue() + ", 日：" + ldt2.getDayOfMonth()
                + ", 小时：" + ldt2.getHour() + ", 分钟：" + ldt2.getMinute() + ", 秒：" + ldt2.getSecond());
    }
}

5.Instant

package com.szh.java8.datetime;

import java.time.Instant;
import java.time.OffsetDateTime;
import java.time.ZoneOffset;


public class TestInstant {

    public static void main(String[] args) {
        Instant instant1 = Instant.now();
        System.out.println(instant1);

        OffsetDateTime odt = instant1.atOffset(ZoneOffset.ofHoursMinutesSeconds(8,16,32));
        System.out.println(odt);

        System.out.println(instant1.getEpochSecond());
        System.out.println(instant1.toEpochMilli());

        Instant instant2 = Instant.ofEpochSecond(1000);
        System.out.println(instant2);

        Instant instant3 = instant1.plusSeconds(30);
        System.out.println(instant3);

        Instant instant4 = instant1.minusSeconds(50);
        System.out.println(instant4);
    }
}

6.Duration、Period

package com.szh.java8.datetime;

import java.time.Duration;
import java.time.LocalDate;
import java.time.LocalTime;
import java.time.Period;


public class TestPeriodDuration {

    public static void main(String[] args) {
        LocalDate ld1 = LocalDate.now();
        LocalDate ld2 = LocalDate.of(2020,5,1);
        Period period = Period.between(ld2,ld1);
        System.out.println("两个日期相差：" + period.getYears() + "年，" + period.getMonths() + "个月，"
                            + period.getDays() + "天....");
        System.out.println(period.isNegative()); //检查此期间的三个单位是否为负
        System.out.println(period.isZero()); //检查此期间的所有三个单位是否为零

        System.out.println("--------------------------------------------");

        LocalTime lt1 = LocalTime.now();
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        LocalTime lt2 = LocalTime.now();
        Duration duration = Duration.between(lt1,lt2);
        System.out.println("两个时间相差：" + duration.toHours() + "个小时，" + duration.toMinutes() + "分钟，"
                            + duration.getSeconds() + "秒....");
        System.out.println(duration.isNegative()); //检查此期间的三个单位是否为负
        System.out.println(duration.isZero()); //检查此期间的所有三个单位是否为零
    }
}

7.TestTemporalAdjuster、TestTemporalAdjusters

package com.szh.java8.datetime;

import java.time.DayOfWeek;
import java.time.LocalDateTime;
import java.time.temporal.TemporalAdjusters;


public class TestTemporalAdjuster {

    public static void main(String[] args) {
        LocalDateTime ldt1 = LocalDateTime.now();
        System.out.println(ldt1);

        LocalDateTime ldt2 = ldt1.withMonth(5);
        System.out.println(ldt2);

        LocalDateTime ldt3 = ldt1.with(TemporalAdjusters.next(DayOfWeek.SATURDAY));
        System.out.println(ldt3);

        //自定义：下一个工作日
        LocalDateTime ldt4 = ldt1.with((l) -> {
            LocalDateTime ldt5 = (LocalDateTime) l;
            DayOfWeek dow = ldt5.getDayOfWeek();

            if (dow.equals(DayOfWeek.FRIDAY)) {
                return ldt5.plusDays(3);
            } else if (dow.equals(DayOfWeek.SATURDAY)) {
                return ldt5.plusDays(2);
            } else {
                return ldt5.plusDays(1);
            }
        });
        System.out.println(ldt4);
    }
}

8.DateTimeFormatter

package com.szh.java8.datetime;

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;


public class TestDateTimeFormatter {

    public static void main(String[] args) {
        DateTimeFormatter dtf1 = DateTimeFormatter.ISO_LOCAL_DATE_TIME;
        LocalDateTime ldt1 = LocalDateTime.now();

        String strDate1 = ldt1.format(dtf1);
        System.out.println(strDate1);

        System.out.println("-----------------------------------");

        DateTimeFormatter dtf2 = DateTimeFormatter.ofPattern("yyyy年MM月dd日 HH:mm:ss");
        String strDate2 = ldt1.format(dtf2);
        System.out.println(strDate2);

        System.out.println("-----------------------------------");

        LocalDateTime newDate = ldt1.parse(strDate2, dtf2);
        System.out.println(newDate);
    }
}

Java8新特性——新一套日期时间API

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