JDK1.8 & 日期和时间的使用

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JDK1.8 中增加了一套全新的日期时间API，这套API设计合理，是线程安全的，API的位于java.time包下。

• LocalDate： 表示日期，返回格式为 yyyy-MM-HH 即 1970-01-01
• LocalTime： 表示时间，返回格式为 hh:mm:ss 即 23:59:59.999999999
• LocalDateTime：表示日期时间，返回格式为 yyyy-MM-HH T hh:mm:ss 即 2007-12-03T10:15:30.11
• DateTimeFormatter: 日期时间格式转化类
• Instant：时间戳，表示一个时间戳
• Duration：计算2个时间的距离
• Period：计算2个日期的距离
• ZoneDateTime: 包含时区的时间 JDK1.8还提供了 4 套其他的历法
• ThaiBuddhistDate：泰国的佛教历
• JapaneseDate：日本历
• HijrahDate：伊斯兰历 这里我们说三个感性却可以多了解一下第四个。

java.time 包下的类

常见的操作

创建指定日期 以及一些获取

测试：

public static void main(String[] args) {
    //创建指定日期
    LocalDate f= LocalDate.of(2021,05,23);
    System.out.println("f = " + f);
    //获取当前日期
    LocalDate now = LocalDate.now();
    System.out.println("now = " + now);

    //获取LocalDate 对应的 年 月 日
    System.out.println("now.getYear() = " + now.getYear());
    //获取月份
    System.out.println("now.getMonth() = " + now.getMonth().getValue());
    //这个月 的第几天
    System.out.println("now.getDayOfMonth() = " + now.getDayOfMonth());
    //一周的星期几
    System.out.println("now.getDayOfWeek() = " + now.getDayOfWeek());
    //一年的第几天
    System.out.println("now.getDayOfYear() = " + now.getDayOfYear());
}

输出结果：

f = 2021-05-23
now = 2022-06-05
now.getYear() = 2022
now.getMonth() = 6
now.getDayOfMonth() = 5
now.getDayOfWeek() = SUNDAY
now.getDayOfYear() = 156

创建时间

测试：

public static void main(String[] args) {
    //获取当前时间
    LocalTime now = LocalTime.now();
    System.out.println("now = " + now);
    System.out.println("now.getHour() = " + now.getHour());
    System.out.println("now.getMinute() = " + now.getMinute());
    System.out.println("now.getSecond() = " + now.getSecond());
    System.out.println("now.getNano() = " + now.getNano());
    //获取指定的 时间
    LocalTime of = LocalTime.of(11, 23, 20, 1111);
    System.out.println("of = " + of);
}

输出结果：

now = 11:25:16.782
now.getHour() = 11
now.getMinute() = 25
now.getSecond() = 16
now.getNano() = 782000000
of = 11:23:20.000001111

日期的修改和比较

测试 日期修改：

public static void main(String[] args) {
    LocalDateTime now = LocalDateTime.now();
    System.out.println("now = " + now);
    //修改年份 获取到新的LocalDateTime 不会修改原来的 LocalDateTime对象 其他的值修改也是同理
    LocalDateTime localDateTime = now.withYear(2088);
    System.out.println("localDateTime = " + localDateTime);
    //两天后的时间 当然也有 年 月的方法
    LocalDateTime localDateTime1 = now.plusDays(2);
    System.out.println("localDateTime1 = " + localDateTime1);
    //两天前的时间 当然也有 年 月的方法
    LocalDateTime localDateTime2 = now.minusDays(2);
    System.out.println("localDateTime2 = " + localDateTime2);
}

输出结果：

now = 2022-06-05T11:33:46.725
localDateTime = 2088-06-05T11:33:46.725
localDateTime1 = 2022-06-07T11:33:46.725
localDateTime2 = 2022-06-03T11:33:46.725

测试 日期比较

public static void main(String[] args) {
    LocalDate now = LocalDate.now();
    LocalDate of = LocalDate.of(2023, 5, 1);
    System.out.println("now.isAfter(of) = " + now.isAfter(of));//在他之后
    System.out.println("now.isBefore(of) = " + now.isBefore(of));//在他之前
    System.out.println("now.isEqual(of) = " + now.isEqual(of));//是否是同一个时间
}

输出结果：

now.isAfter(of) = false
now.isBefore(of) = true
now.isEqual(of) = false

日期格式化

测试：

public static void main(String[] args) {
    LocalDateTime now = LocalDateTime.now();
    DateTimeFormatter dateTimeFormatter= DateTimeFormatter.ISO_LOCAL_DATE_TIME;
    String format = now.format(dateTimeFormatter);
    System.out.println("format = " + format);
}

DateTimeFormatter.ISO_LOCAL_DATE_TIME;

public static final DateTimeFormatter ISO_LOCAL_DATE_TIME;
static {
    ISO_LOCAL_DATE_TIME = new DateTimeFormatterBuilder()
            .parseCaseInsensitive()
            .append(ISO_LOCAL_DATE)
            .appendLiteral('T')
            .append(ISO_LOCAL_TIME)
            .toFormatter(ResolverStyle.STRICT, IsoChronology.INSTANCE);
}

输出结果：

format = 2022-06-05T11:43:30.964

当然我们也可以指定特定的格式进行格式化
测试：

public static void main(String[] args) {
    LocalDateTime now = LocalDateTime.now();
    DateTimeFormatter dateTimeFormatter= DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    String format = now.format(dateTimeFormatter);
    System.out.println("format = " + format);
}

输出结果：

format = 2022-06-05 11:45:05

计算时间日期的差值

测试：

public static void main(String[] args) {
    LocalTime now = LocalTime.now();
    System.out.println("now = " + now);
    LocalTime of = LocalTime.of(13, 48, 59);
    System.out.println("of = " + of);
    Duration duration = Duration.between(now, of);
    //差几天
    System.out.println("duration.toDays() = " + duration.toDays());
    //差几小时
    System.out.println("duration.toHours() = " + duration.toHours());
    //差几分钟
    System.out.println("duration.toMinutes() = " + duration.toMinutes());
    //差几秒
    System.out.println("duration.toMillis() = " + duration.toMillis());
    System.out.println("========================================");
    LocalDate now1 = LocalDate.now();
    System.out.println("now1 = " + now1);
    LocalDate of1 = LocalDate.of(2025, 6, 5);
    System.out.println("of1 = " + of1);
    Period between = Period.between(now1, of1);
    //差几年
    System.out.println("between.getYears() = " + between.getYears());
    //差几月
    System.out.println("between.getMonths() = " + between.getMonths());
    //差几日
    System.out.println("between.getDays() = " + between.getDays());
}

输出结果：

now = 12:02:53.234
of = 13:48:59
duration.toDays() = 0
duration.toHours() = 1
duration.toMinutes() = 106
duration.toMillis() = 6365766
========================================
now1 = 2022-06-05
of1 = 2025-06-05
between.getYears() = 3
between.getMonths() = 0
between.getDays() = 0

TemporalAdjusters 和 TemporalAdjuster 的使用

public static void main(String[] args) {
    LocalDateTime localDateTime =LocalDateTime.now();
    System.out.println("localDateTime = " + localDateTime);
    //函数时接口实现
    TemporalAdjuster adjuster =(temporal)->{
        LocalDateTime lo= (LocalDateTime) temporal;
        LocalDateTime localDateTime1 = lo.plusMonths(1).withDayOfMonth(1);
        System.out.println("函数式接口 TemporalAdjuster="+localDateTime1);
        return localDateTime1;
    };
    LocalDateTime with1 = localDateTime.with(adjuster);
    System.out.println("TemporalAdjuster "+with1);

    //这里直接使用TemporalAdjusters的静态方法
    LocalDateTime with = localDateTime.with(TemporalAdjusters.firstDayOfNextMonth());
    System.out.println("TemporalAdjusters static = " + with);

}

输出结果：

localDateTime = 2022-06-05T12:16:51.863
函数式接口 TemporalAdjuster=2022-07-01T12:16:51.863
TemporalAdjuster 2022-07-01T12:16:51.863
TemporalAdjusters static = 2022-07-01T12:16:51.863

实践是检验真理的唯一方法！ 明天见🥰🥰🥰