一文帶你搞懂Java8的LocalDateTime

更新時(shí)間：2023年04月06日 09:05:57 作者：Java技術(shù)指北

LocalDateTime?是Java8中新加入的日期時(shí)間類，現(xiàn)在都?Java20?了，不會(huì)還有人沒用過?LocalDateTime?吧？今天給大家演示一下?LocalDateTime?的常用方法

獲取當(dāng)前時(shí)間
獲取當(dāng)前時(shí)間的年月日時(shí)分秒
給LocalDateTime賦值
時(shí)間與字符串相互轉(zhuǎn)換
時(shí)間運(yùn)算：加上對(duì)應(yīng)時(shí)間
時(shí)間運(yùn)算：減去對(duì)應(yīng)時(shí)間
兩個(gè)時(shí)間比較
利用Duration計(jì)算時(shí)間差
改變當(dāng)前時(shí)間的年月日時(shí)分秒
自定義輸出的格式
LocalDateTime的with()方法
兩個(gè)日期前后的比較與判斷

結(jié)束語

前言

LocalDateTime、LocalDate、LocalTime 是 Java8 全新的日期框架，加強(qiáng)了對(duì)時(shí)間的管理，有很多特別好用的時(shí)間運(yùn)算方法，而且是線程安全的，較之前的 util.Date 以及 Calander 使用起來更加的方便直觀，下面介紹幾種常見的日期對(duì)象用法。

LocalDateTime：日期加時(shí)間的日期對(duì)象，包含年月日時(shí)分秒
LocalDate：日期類，包含年月日
LocalTime：時(shí)間類，包含時(shí)分秒

LocalDateTime

獲取當(dāng)前時(shí)間

@Test
public?void?test()?{
????LocalDate?localDate?=?LocalDate.now();
????LocalTime?localTime?=?LocalTime.now();
????LocalDateTime?localDateTime?=?LocalDateTime.now();
????System.out.println("localDate:"+localDate);//2023-02-22
????System.out.println("localTime:"+localTime);//17:25:36.590
????System.out.println("localDateTime:"+localDateTime);//2023-02-22T17:25:36.590
}

輸出結(jié)果：

可以看到不用做格式轉(zhuǎn)換就可以得到可讀性很高的日期格式。注意：ISO 8601規(guī)定的日期和時(shí)間分隔符是T。標(biāo)準(zhǔn)格式如下：

日期：yyyy-MM-dd
時(shí)間：HH:mm:ss
帶毫秒的時(shí)間：HH:mm:ss.SSS
日期和時(shí)間：yyyy-MM-dd'T'HH:mm:ss
帶毫秒的日期和時(shí)間：yyyy-MM-dd'T'HH:mm:ss.SSS

獲取當(dāng)前時(shí)間的年月日時(shí)分秒

@Test
public?void?test()?{
????LocalDateTime?localDateTime?=?LocalDateTime.now();?//?獲取當(dāng)前時(shí)間
????int?year?=?localDateTime.getYear();?//?獲取年份?2023
????int?month?=?localDateTime.getMonthValue();?//?獲取月份?2
????int?day?=?localDateTime.getDayOfMonth();?//?獲取月中的天數(shù)?22
????int?hour?=?localDateTime.getHour();?//?獲取當(dāng)前的小時(shí)?17
????int?minute?=?localDateTime.getMinute();?//?獲取當(dāng)前分鐘?33
????int?second?=?localDateTime.getSecond();?//?獲取當(dāng)前秒數(shù)?22
????System.out.println(year);
????System.out.println(month);
????System.out.println(day);
????System.out.println(hour);
????System.out.println(minute);
????System.out.println(second);
}

輸出結(jié)果：

給LocalDateTime賦值

在static目錄中新建kaptcha.html頁面,代碼如下：

public?void?test()?{
????LocalDateTime?of?=?LocalDateTime.of(2023,2,22,22,22,22);
????System.out.println(of);?//?輸出2023-02-22T22:22:22
}

時(shí)間與字符串相互轉(zhuǎn)換

@Test
public?void?test()?{
????//?將字符串轉(zhuǎn)換為指定格式的時(shí)間（格式要和給定的格式一致，不然會(huì)報(bào)錯(cuò)）
????LocalDateTime?parse?=?LocalDateTime.parse("2023-02-22?22:22:22",?DateTimeFormatter.ofPattern("yyyy-MM-dd?HH:mm:ss"));
????LocalDateTime?parse1?=?LocalDateTime.parse("2023?02?22?22:22:22",?DateTimeFormatter.ofPattern("yyyy?MM?dd?HH:mm:ss"));
????LocalDateTime?parse2?=?LocalDateTime.parse("2023.02.22?22:22:22",?DateTimeFormatter.ofPattern("yyyy.MM.dd?HH:mm:ss"));
????System.out.println(parse);?//?輸出2023-02-22T22:22:22
????System.out.println(parse1);?//?輸出2023-02-22T22:22:22
????System.out.println(parse2);?//?輸出2023-02-22T22:22:22
????//?時(shí)間轉(zhuǎn)字符串
????LocalDateTime?now?=?LocalDateTime.now();
????DateTimeFormatter?of?=?DateTimeFormatter.ofPattern("yyyy-MM-dd?HH:mm:ss");
????String?dateTime?=?now.format(of);
????System.out.println(dateTime);?//?輸出?2023-02-22?17:56:18
}

輸出結(jié)果：

時(shí)間運(yùn)算：加上對(duì)應(yīng)時(shí)間

LocalDateTime提供了對(duì)日期和時(shí)間進(jìn)行加減的非常簡(jiǎn)單的鏈?zhǔn)秸{(diào)用，讓時(shí)間運(yùn)算變得非常簡(jiǎn)單：

@Test
public?void?test()?{
????LocalDateTime?now?=?LocalDateTime.now();?//?當(dāng)前時(shí)間2023-02-22T18:00:19.352
????LocalDateTime?plusYears=?now.plusYears(2);?//?在當(dāng)前時(shí)間加上2年2025-02-22T18:00:19.352
????LocalDateTime?plusMonths=?now.plusMonths(2);//?在當(dāng)前時(shí)間商加上2月2023-04-22T18:00:19.352
????LocalDateTime?plusDays=?now.plusDays(2);?//?在當(dāng)前時(shí)間加上2天2023-02-24T18:00:19.352
????LocalDateTime?plusHours=?now.plusHours(2);?//?在當(dāng)前時(shí)間加上2個(gè)小時(shí)2023-02-22T20:00:19.352
????LocalDateTime?plusMinutes=?now.plusMinutes(30);?//?在當(dāng)前時(shí)間加上30分鐘2023-02-22T18:30:19.352
????LocalDateTime?plusSeconds?=?now.plusSeconds(30);?//?在當(dāng)前時(shí)間加上30秒2023-02-22T18:00:49.352
????System.out.println(now);
????System.out.println(plusYears);
????System.out.println(plusMonths);
????System.out.println(plusDays);
????System.out.println(plusHours);
????System.out.println(plusMinutes);
????System.out.println(plusSeconds);
}

輸出結(jié)果：

時(shí)間運(yùn)算：減去對(duì)應(yīng)時(shí)間

@Test
public?void?test()?{
????LocalDateTime?now?=?LocalDateTime.now();?//?當(dāng)前時(shí)間
????LocalDateTime?minusYears?=?now.minusYears(2);?//?在當(dāng)前時(shí)間減上2年
????LocalDateTime?minusMonths?=?now.minusMonths(2);//?在當(dāng)前時(shí)間商減上2月
????LocalDateTime?minusDays?=?now.minusDays(2);?//?在當(dāng)前時(shí)間減上2天
????LocalDateTime?minusHours?=?now.minusHours(2);?//?在當(dāng)前時(shí)間減上2個(gè)小時(shí)
????LocalDateTime?minusMinutes?=?now.minusMinutes(30);?//?在當(dāng)前時(shí)間減上30分鐘
????LocalDateTime?minusSeconds?=?now.minusSeconds(30);?//?在當(dāng)前時(shí)間減上30秒
????System.out.println("now:"?+?now);
????System.out.println("minusYears:"?+?minusYears);
????System.out.println("minusMonths:"?+?minusMonths);
????System.out.println("minusDays:"?+?minusDays);
????System.out.println("minusHours:"?+?minusHours);
????System.out.println("minusMinutes:"?+?minusMinutes);
????System.out.println("minusSeconds:"?+?minusSeconds);
}

輸出結(jié)果：

兩個(gè)時(shí)間比較

@Test
public?void?test()?{
????LocalDateTime?now?=?LocalDateTime.now();?//?當(dāng)前時(shí)間
????LocalDateTime?now1?=?now.plusYears(5);?//?在當(dāng)前時(shí)間加上5年
????//??給LocalDateTime?賦值
????LocalDateTime?of?=?LocalDateTime.of(2023,2,2,22,22,22);
????LocalDateTime?of1?=?LocalDateTime.of(2023,8,5,1,1,1);
????//兩個(gè)時(shí)間作比較，第一個(gè)時(shí)間減去第二個(gè)時(shí)間(如果年份相同，比較月份，月份相同比較天數(shù)，以此類推)
????int?compareTo?=?now1.compareTo(now);
????int?compareTo1?=?now.compareTo(now1);
????int?compareTo2?=?now.compareTo(of);
????int?compareTo3?=?now.compareTo(of1);
????System.out.println(now);???//?輸出?2023-02-22T20:19:44.112v
????System.out.println(now1);?//?輸出?2028-02-22T20:19:44.112
????System.out.println(of);?//?輸出?2023-02-02T22:22:22
????System.out.println(of1);?//?輸出?2023-08-05T01:01:01
????System.out.println(compareTo);?//?輸出?5
????System.out.println(compareTo1);?//?輸出?-5
????System.out.println(compareTo2);?//?輸出?20
????System.out.println(compareTo3);?//?輸出?-6
}

輸出結(jié)果：

利用Duration計(jì)算時(shí)間差

注意沒有計(jì)算相差的年和秒值，對(duì)于要計(jì)算相差的秒數(shù)，可以利用計(jì)算毫秒來進(jìn)行轉(zhuǎn)換

@Test
public?void?test()?{
????LocalDateTime?now?=?LocalDateTime.now();?//?當(dāng)前時(shí)間
????//??給LocalDateTime?賦值
????LocalDateTime?of?=?LocalDateTime.of(2022,2,22,2,2,2);
????Duration?duration?=?Duration.between(of,now);?//?后面減去前面
????long?toDays?=?Duration.between(of,now).toDays();?//相差的天數(shù)
????long?toHours?=?Duration.between(of,now).toHours();//相差的小時(shí)數(shù)
????long?toMinutes?=?Duration.between(of,now).toMinutes();//相差的分鐘數(shù)
????long?toMillis?=?Duration.between(of,now).toMillis();//相差毫秒數(shù)
????long?toNanos?=?Duration.between(of,now).toNanos();//相差的納秒數(shù)
????System.out.println("toDays:"+?toDays);?//?輸出?toDays:365
????System.out.println("toHours:"+?toHours);?//?輸出?toHours:8778
????System.out.println("toMinutes:"+?toMinutes);?//?輸出?toMinutes:526732
????System.out.println("toMillis:"+?toMillis);?//?輸出?toMillis:31603973840
????System.out.println("toNanos:"+?toNanos);?//?輸出?toNanos:31603973840000000
}

輸出結(jié)果：

改變當(dāng)前時(shí)間的年月日時(shí)分秒

@Test
public?void?test()?{
????LocalDateTime?now?=?LocalDateTime.now();?//?當(dāng)前時(shí)間
????LocalDateTime?withYear?=?now.withYear(2060);?//?改變當(dāng)前年份（變成2060年）
????LocalDateTime?withMonth?=?now.withMonth(12);?//?改變當(dāng)前月份（變成12月份）
????LocalDateTime?withDayOfMonth?=?now.withDayOfMonth(28);?//改變當(dāng)前天數(shù)（變成28日）
????LocalDateTime?withHour?=?now.withHour(23);?//?改變當(dāng)前小時(shí)數(shù)（變成23時(shí)）
????LocalDateTime?withMinute?=?now.withMinute(30);?//?改變當(dāng)前分鐘（變成30分鐘）
????LocalDateTime?withSecond?=?now.withSecond(23);?//?改變當(dāng)前小時(shí)數(shù)（變成23時(shí)）
????LocalDateTime?withDayOfYear?=?now.withDayOfYear(60);?//?從一月一號(hào)開始加上60天
????System.out.println(now);
????System.out.println("withYear:"+?withYear);
????System.out.println("withMonth:"+?withMonth);
????System.out.println("withDayOfMonth:"+?withDayOfMonth);
????System.out.println("withHour:"+?withHour);
????System.out.println("withMinute:"+?withMinute);
????System.out.println("withSecond:"+?withSecond);
????System.out.println("withDayOfYear:"+?withDayOfYear);
}

輸出結(jié)果：

自定義輸出的格式

@Test
public?void?test()?{
????//?自定義格式化:
????DateTimeFormatter?dtf?=?DateTimeFormatter.ofPattern("yyyy/MM/dd?HH:mm:ss");
????DateTimeFormatter?dtf1?=?DateTimeFormatter.ofPattern("yyyy.MM.dd?HH:mm:ss");
????System.out.println("自定義格式y(tǒng)yyy/MM/dd HH:mm:ss ："+dtf.format(LocalDateTime.now()));
????System.out.println("自定義格式y(tǒng)yyy.MM.dd HH:mm:ss ："+dtf1.format(LocalDateTime.now()));

????//?用自定義格式解析:
????LocalDateTime?dt2?=?LocalDateTime.parse("2020/10/20?15:16:17",?dtf);
????System.out.println("格式解析:"+dt2);
}

輸出結(jié)果：

LocalDateTime的with()方法

@Test
public?void?test()?{
????//?本月第一天0:00時(shí)刻:
????LocalDateTime?firstDay?=?LocalDate.now().withDayOfMonth(1).atStartOfDay();
????//?本月最后1天:
????LocalDate?lastDay?=?LocalDate.now().with(TemporalAdjusters.lastDayOfMonth());
????//?下月第1天:
????LocalDate?nextMonthFirstDay?=?LocalDate.now().with(TemporalAdjusters.firstDayOfNextMonth());
????//?本月第1個(gè)周一:
????LocalDate?firstWeekday?=?LocalDate.now().with(TemporalAdjusters.firstInMonth(DayOfWeek.MONDAY));
}

兩個(gè)日期前后的比較與判斷

@Test
public?void?test()?{
????//判斷兩個(gè)時(shí)間點(diǎn)的前后
????LocalDateTime?now?=?LocalDateTime.now();
????LocalDateTime?target?=?LocalDateTime.of(2022,?2,?22,?22,?22,?22);
????boolean?isBefore?=?now.isBefore(target);
????System.out.println("now:"+now);
????System.out.println("target:"+target);
????System.out.println("isBefore:"+isBefore);
????System.out.println(LocalDate.now().isBefore(LocalDate.of(2022,?2,?22)));
????System.out.println(LocalTime.now().isAfter(LocalTime.parse("08:15:00")));
}

輸出結(jié)果：