深入理解Java8新特性之新日期時(shí)間API的應(yīng)用

更新時(shí)間：2021年11月11日 08:55:51 作者：張起靈-小哥

自從 14 年發(fā)布 Java 8 以后，我們古老 java.util.Date 終于不再是我們 Java 里操作日期時(shí)間的唯一的選擇，其實(shí) Java 里的日期時(shí)間的相關(guān) API 一直為世猿詬病，今天我們來(lái)了解新的日期時(shí)間API是怎么使用吧

1.新舊對(duì)比（線程安全問(wèn)題）

我們先來(lái)看下面的代碼：👇👇👇 （關(guān)于代碼中某些類(lèi)中的某些方法，我在這里就不說(shuō)了，大家可以去查找api文檔）

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<Date> task1 = new Callable<Date>() {
            @Override
            public Date call() throws Exception {
                return sdf.parse("20211109");
            }
        };
 
        ExecutorService pool1 = Executors.newFixedThreadPool(10);
        List<Future<Date>> futureList1 = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            futureList1.add(pool1.submit(task1));
        }
 
        for (Future<Date> future : futureList1) {
            System.out.println(future.get());
        }
 
        pool1.shutdown();
 
        //=================================================================
 
//        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyyMMdd");
//
//        Callable<LocalDate> task2 = new Callable<LocalDate>() {
//            @Override
//            public LocalDate call() throws Exception {
//                return LocalDate.parse("20211109",dtf);
//            }
//        };
//
//        ExecutorService pool2 = Executors.newFixedThreadPool(10);
//        List<Future<LocalDate>> futureList2 = new ArrayList<>();
//        for (int i = 0; i < 10; i++) {
//            futureList2.add(pool2.submit(task2));
//        }
//
//        for (Future<LocalDate> future : futureList2) {
//            System.out.println(future.get());
//        }
//
//        pool2.shutdown();
    }
}

運(yùn)行之后，就出現(xiàn)了線程安全問(wèn)題。

將代碼中的上半部分注釋掉，然后打開(kāi)下半部分的代碼，再次運(yùn)行，線程安全問(wèn)題就不存在了。

也就是Java8中提供了新一套日期時(shí)間API已經(jīng)解決了線程安全問(wèn)題。

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("小時(shí)：" + lt1.getHour() + ", 分鐘：" + 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()
                + ", 小時(shí)：" + ldt2.getHour() + ", 分鐘：" + ldt2.getMinute() + ", 秒：" + ldt2.getSecond());
    }
}

5.Instant

package com.szh.java8.datetime;
 
import java.time.Instant;
import java.time.OffsetDateTime;
import java.time.ZoneOffset;
 
/**
 * Instant : 時(shí)間戳（使用 Unix 元年  1970年1月1日 00:00:00 所經(jīng)歷的毫秒值）
 *           默認(rèn)使用 UTC 時(shí)區(qū)
 */
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;
 
/**
 * Period : 用于計(jì)算兩個(gè)“日期”間隔
 * Duration : 用于計(jì)算兩個(gè)“時(shí)間”間隔
 */
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("兩個(gè)日期相差：" + period.getYears() + "年，" + period.getMonths() + "個(gè)月，"
                            + period.getDays() + "天....");
        System.out.println(period.isNegative()); //檢查此期間的三個(gè)單位是否為負(fù)
        System.out.println(period.isZero()); //檢查此期間的所有三個(gè)單位是否為零
 
        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("兩個(gè)時(shí)間相差：" + duration.toHours() + "個(gè)小時(shí)，" + duration.toMinutes() + "分鐘，"
                            + duration.getSeconds() + "秒....");
        System.out.println(duration.isNegative()); //檢查此期間的三個(gè)單位是否為負(fù)
        System.out.println(duration.isZero()); //檢查此期間的所有三個(gè)單位是否為零
    }
}

7.TestTemporalAdjuster、TestTemporalAdjusters

package com.szh.java8.datetime;
 
import java.time.DayOfWeek;
import java.time.LocalDateTime;
import java.time.temporal.TemporalAdjusters;
 
/**
 *  TemporalAdjuster : 時(shí)間校正器。有時(shí)我們可能需要獲取例如：將日期調(diào)整到“下個(gè)周日”等操作。
 *  TemporalAdjusters : 該類(lèi)通過(guò)靜態(tài)方法提供了大量的常用 TemporalAdjuster 的實(shí)現(xiàn)。
 */
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);
 
        //自定義：下一個(gè)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;
 
/**
 * 解析與格式化
 */
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);
    }
}