一、舊時(shí)間日期問(wèn)題

1. 在 java.util 和 java.sql 包下都有時(shí)間日期類

   • java.util.Date 類包含時(shí)間和日期

   • java.sql.Date 類值包含日期

2. java.util.Date 類線程不安全，Date 對(duì)象可變

3. 時(shí)間日期格式化類在 java.text 包下

4. 時(shí)區(qū)處理困難，并不支持國(guó)際化，沒(méi)有時(shí)區(qū)支持

package com.my.olddate;import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;public class OldDateTest {public static void main(String[] args) {// 設(shè)計(jì)不合理Date date = new Date(2022, 7, 30);System.out.println(date); // Wed Aug 30 00:00:00 CST 3922System.out.println("--------------------");// 存在線程安全問(wèn)題SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");for (int i = 0; i < 50; i++) {new Thread(() -> {try {System.out.println(simpleDateFormat.parse("2022-07-30"));} catch (ParseException e) {e.printStackTrace();}}).start();}}
}

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二、新時(shí)間日期概述

1、基本介紹

• JDK 8 增加了一套全新的時(shí)間日期 API，這套 API 設(shè)計(jì)合理，線程安全

• 新時(shí)間日期 API 位于 java.time 包下

2、關(guān)鍵類介紹

類	說(shuō)明
LocalDate	日期，年月日
LocalTime	時(shí)間，時(shí)分秒
LocalDateTime	日期時(shí)間，年月日時(shí)分秒
DateTimeFormatter	日期時(shí)間格式化類
Instant	時(shí)間戳，時(shí)間瞬間
Duration	計(jì)算時(shí)間差
Period	計(jì)算日期差
ZonedDateTime	包含時(shí)區(qū)的時(shí)間

• Java 中使用的是 ISO 8601 日期和時(shí)間的表示方法，是世界民用歷法，即公歷，平年有 365 天，閏年有 366 天

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三、新時(shí)間日期操作

1、新時(shí)間日期創(chuàng)建

• 創(chuàng)建指定日期

LocalDate date1 = LocalDate.of(2022, 6, 30);
System.out.println(date1);

• 創(chuàng)建當(dāng)前日期

LocalDate date2 = LocalDate.now();
System.out.println(date2);

• 創(chuàng)建指定時(shí)間

LocalTime time1 = LocalTime.of(15, 30, 30, 123);
System.out.println(time1);

• 創(chuàng)建當(dāng)前時(shí)間

LocalTime time2 = LocalTime.now();
System.out.println(time2);

• 創(chuàng)建指定日期時(shí)間

LocalDateTime localDateTime1 = LocalDateTime.of(2022, 6, 30, 15, 30, 30, 123);
System.out.println(localDateTime1);

• 創(chuàng)建當(dāng)前日期時(shí)間

LocalDateTime localDateTime2 = LocalDateTime.now();
System.out.println(localDateTime2);

2、新時(shí)間日期信息獲取

• LocalDate 對(duì)象信息獲取

LocalDate localDate = LocalDate.now();System.out.println("年：" + localDate.getDayOfYear());
System.out.println("月：" + localDate.getMonth().getValue() + "  " + localDate.getMonth());
System.out.println("日：" + localDate.getDayOfMonth());
System.out.println("星期：" + localDate.getDayOfWeek().getValue() + "  " + localDate.getDayOfWeek());

• LocalTime 對(duì)象信息獲取

LocalTime localTime = LocalTime.now();System.out.println("時(shí)：" + localTime.getHour());
System.out.println("分：" + localTime.getMinute());
System.out.println("秒：" + localTime.getSecond());
System.out.println("納秒：" + localTime.getNano());

• LocalDateTime 對(duì)象信息獲取

LocalDateTime localDateTime = LocalDateTime.now();System.out.println("年：" + localDateTime.getDayOfYear());
System.out.println("月：" + localDateTime.getMonth().getValue() + "  " + localDateTime.getMonth());
System.out.println("日：" + localDateTime.getDayOfMonth());
System.out.println("星期：" + localDateTime.getDayOfWeek().getValue() + "  " + localDateTime.getDayOfWeek());
System.out.println("時(shí)：" + localDateTime.getHour());
System.out.println("分：" + localDateTime.getMinute());
System.out.println("秒：" + localDateTime.getSecond());
System.out.println("納秒" + localDateTime.getNano());

3、新時(shí)間日期修改

• 通過(guò)設(shè)置時(shí)間日期進(jìn)行修改

LocalDateTime now = LocalDateTime.now();System.out.println("當(dāng)前日期時(shí)間：" + now);
System.out.println("修改年：" + now.withYear(2000));
System.out.println("修改月：" + now.withMonth(10));
System.out.println("修改日：" + now.withDayOfMonth(25));
System.out.println("修改時(shí)：" + now.withHour(20));
System.out.println("修改分：" + now.withMinute(10));
System.out.println("修改秒：" + now.withSecond(30));
System.out.println("修改納秒：" + now.withNano(123456));

• 通過(guò)加減時(shí)間日期進(jìn)行修改

LocalDateTime now = LocalDateTime.now();System.out.println("五年后：" + now.plusYears(5));
System.out.println("五個(gè)月后：" + now.plusMonths(5));
System.out.println("五天后：" + now.plusDays(5));
System.out.println("五小時(shí)后：" + now.plusHours(5));
System.out.println("五分鐘后：" + now.plusMinutes(5));
System.out.println("五秒后：" + now.plusSeconds(5));
System.out.println("五納秒后：" + now.plusNanos(5));System.out.println("--------------------");System.out.println("五年前：" + now.minusYears(5));
System.out.println("五個(gè)月前：" + now.minusMonths(5));
System.out.println("五天前：" + now.minusDays(5));
System.out.println("五小時(shí)前：" + now.minusHours(5));
System.out.println("五分鐘前：" + now.minusMinutes(5));
System.out.println("五秒前：" + now.minusSeconds(5));
System.out.println("五納秒前：" + now.minusNanos(5));

4、新時(shí)間日期線程安全問(wèn)題

• 新時(shí)間日期類每次修改都會(huì)創(chuàng)建新的對(duì)象，原來(lái)的對(duì)象是不會(huì)被修改的，不會(huì)存在線程安去問(wèn)題

package com.my.newdate;import java.time.LocalDateTime;public class NewDateSafeTest {public static void main(String[] args) {LocalDateTime now = LocalDateTime.now();LocalDateTime localDateTime = now.plusYears(5);System.out.println(now + "  " + now.hashCode());System.out.println(localDateTime + "  " + localDateTime.hashCode());}
}

5、新時(shí)間日期比較

package com.my.newdate;import java.time.LocalDateTime;public class NewDateCompareTest {public static void main(String[] args) {LocalDateTime now = LocalDateTime.now();LocalDateTime localDateTime = LocalDateTime.of(2020, 1, 1, 15, 30, 30);System.out.println(now.isAfter(localDateTime));System.out.println(now.isBefore(localDateTime));System.out.println(now.isEqual(localDateTime));}
}

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四、新時(shí)間日期格式化與解析

• 使用 java.time.format.DateTimeFormatter 進(jìn)行格式化和解析操作

1、新時(shí)間日期格式化

• 使用系統(tǒng)默認(rèn)格式進(jìn)行格式化

LocalDateTime now = LocalDateTime.now();DateTimeFormatter basicIsoDate = DateTimeFormatter.BASIC_ISO_DATE;String format = now.format(basicIsoDate);
System.out.println(format);

• 使用指定格式進(jìn)行格式化

LocalDateTime now = LocalDateTime.now();DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");String format = now.format(dateTimeFormatter);
System.out.println(format);

2、新時(shí)間日期解析

package com.my.newdate;import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;public class NewDateParseTest {public static void main(String[] args) {String str2 = "2022-07-30 17:36:44";DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");LocalDateTime localDateTime2 = LocalDateTime.parse(str2, dateTimeFormatter);System.out.println(localDateTime2);}
}

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五、時(shí)間戳

1、基本介紹

• Instant 類，時(shí)間戳，可以獲取從 1970-01-01 00:00:00 起的秒數(shù)

2、基本使用

• 獲取時(shí)間戳

Instant now = Instant.now();
System.out.println(now);

• 獲取秒數(shù)

Instant now = Instant.now();System.out.println(now.getEpochSecond());

• 獲取納秒數(shù)

Instant now = Instant.now();System.out.println(now.toEpochMilli());

• 通過(guò)秒數(shù)獲取時(shí)間戳

Instant instant = Instant.ofEpochSecond(1659176030L);
System.out.println(instant);

• 通過(guò)納秒數(shù)獲取時(shí)間戳

Instant instant2 = Instant.ofEpochMilli(1659176030725L);
System.out.println(instant2);

• 耗時(shí)統(tǒng)計(jì)

Instant start = Instant.now();
Thread.sleep(5);
Instant end = Instant.now();
System.out.println("耗時(shí)（納秒）：" + (end.toEpochMilli() - start.toEpochMilli()));

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六、計(jì)算時(shí)間日期差

• Duration 和 Period 類，用來(lái)計(jì)算時(shí)間日期差

1、計(jì)算時(shí)間差

package com.my.newdate;import java.time.Duration;
import java.time.LocalTime;public class DurationTest {public static void main(String[] args) {LocalTime now = LocalTime.now();LocalTime time = LocalTime.of(10, 1, 1);Duration duration = Duration.between(time, now);System.out.println("天數(shù)差：" + duration.toDays());System.out.println("小時(shí)數(shù)差：" + duration.toHours());System.out.println("分鐘數(shù)差：" + duration.toMinutes());System.out.println("秒數(shù)差：" + duration.toMillis());System.out.println("納秒數(shù)差：" + duration.toNanos());}
}

2、計(jì)算日期差

package com.my.newdate;import java.time.LocalDate;
import java.time.Period;public class PeriodTest {public static void main(String[] args) {LocalDate now = LocalDate.now();LocalDate date = LocalDate.of(2020, 1, 1);Period period = Period.between(date, now);System.out.println("年份差：" + period.getYears());System.out.println("月份差：" + period.getMonths());System.out.println("日份差：" + period.getDays());}
}

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七、時(shí)間矯正器

1、TemporalAdjuster

（1）基本介紹

• TemporalAdjuster 是一個(gè)函數(shù)式接口，adjustInto 方法需要傳入一個(gè) Temporal 接口，Temporal 接口的實(shí)現(xiàn)類有LocalDate、LocalTime、LocalDateTime 等

@FunctionalInterface
public interface TemporalAdjuster {Temporal adjustInto(Temporal temporal);
}

（2）基本使用

package com.my.newdate;import java.time.LocalDateTime;
import java.time.temporal.TemporalAdjuster;public class TemporalAdjusterTest {public static void main(String[] args) {// 將當(dāng)前日期調(diào)整為下個(gè)月的第一天LocalDateTime now = LocalDateTime.now();TemporalAdjuster temporalAdjuster = (temporal) -> {LocalDateTime localDateTime = (LocalDateTime) temporal;LocalDateTime nextLocalDateTime = localDateTime.plusMonths(1).withDayOfMonth(1);return nextLocalDateTime;};LocalDateTime nextLocalDateTime = now.with(temporalAdjuster);System.out.println(nextLocalDateTime);}
}

2、TemporalAdjusters

（1）基本介紹

• TemporalAdjusterTests 類有大量靜態(tài)方法提供 TemporalAdjusterTest 接口的實(shí)現(xiàn)

（2）基本使用

package com.my.newdate;import java.time.LocalDateTime;
import java.time.temporal.TemporalAdjusters;public class TemporalAdjustersTest {public static void main(String[] args) {// 將當(dāng)前日期調(diào)整為明年的第一天LocalDateTime now = LocalDateTime.now();LocalDateTime nextLocalDateTime = now.with(TemporalAdjusters.firstDayOfNextYear());System.out.println(nextLocalDateTime);}
}

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八、時(shí)區(qū)

1、基本介紹

• JDK 8 增加了對(duì)時(shí)區(qū)的支持

• LocalDate、LocalTime 和 LocalDateTime 類是不支持時(shí)區(qū)的

• 支持時(shí)區(qū)類：ZonedDate、ZonedTime 和 ZonedDateTime 類

2、基本使用

• 獲取所有時(shí)區(qū) ID

ZoneId.getAvailableZoneIds().forEach(System.out::println);

• 獲取標(biāo)準(zhǔn)時(shí)間，對(duì)比當(dāng)前時(shí)間，我國(guó)使用東八區(qū)，比標(biāo)準(zhǔn)時(shí)間早 8 個(gè)小時(shí)

// 獲取當(dāng)前時(shí)間
LocalDateTime now = LocalDateTime.now();
System.out.println(now);// 獲取標(biāo)準(zhǔn)時(shí)間
ZonedDateTime zonedDateTime = ZonedDateTime.now(Clock.systemUTC());
System.out.println(zonedDateTime);

• 使用計(jì)算機(jī)默認(rèn)時(shí)區(qū)，獲取當(dāng)前時(shí)間

ZonedDateTime zonedDateTime = ZonedDateTime.now();
System.out.println(zonedDateTime);

• 獲取指定時(shí)區(qū)的時(shí)間

ZonedDateTime zonedDateTime2 = ZonedDateTime.now(ZoneId.of("America/Bogota"));
System.out.println(zonedDateTime2);