时间调节器

# 时间调节器

调整时间的高级方法

# TemporalAdjusters

LocalDateTime还有一个通用的 with()方法允许我们做更复杂的运算。with 的参数是 TemporalAdjuster 对象，是一个时间调节器，将一个时间调节成另外一个时间。我们来看看示例代码：

    LocalDateTime dt = LocalDateTime.of(2022,5, 21, 13, 14, 15);

    dt = dt.with(TemporalAdjusters.firstDayOfMonth());
    System.out.println("firstDayOfMonth: " + dt); //2022-05-01T13:14:15

    dt = dt.with(TemporalAdjusters.lastDayOfMonth());
    System.out.println("lastDayOfMonth: " + dt);  //2022-05-31T13:14:15

    dt = dt.with(TemporalAdjusters.next(DayOfWeek.MONDAY)); //找到下一个星期一
    System.out.println("DayOfWeek.MONDAY: " + dt);  //2022-06-06T13:14:15

    dt = dt.with(TemporalAdjusters.firstDayOfNextMonth());  //找到下个月的第一天。
    System.out.println("firstDayOfNextMonth: " + dt);   //2022-07-01T13:14:15


    dt = dt.with(TemporalAdjusters.lastDayOfYear());  //找到一年中的最后一天。
    System.out.println("lastDayOfYear: " + dt);   // 2022-12-31T13:14:15


    dt = dt.with(TemporalAdjusters.firstDayOfYear()); //一年的第一天
    System.out.println("firstDayOfYear: " + dt);  //2022-01-01T13:14:15

    dt = dt.with(TemporalAdjusters.lastInMonth(DayOfWeek.SUNDAY));  //该月的最后一个星期日
    System.out.println("lastInMonth DayOfWeek.SUNDAY: " + dt);  //2022-01-30T13:14:15

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# TemporalAdjuster

我们还可以自定义调节器规则，在规则里写业务逻辑等

TemporalAdjuster taj = t -> t.plus(Period.ofDays(14));  // lambda语法，增加14天
dt = dt.with(taj);
System.out.println(dt); //2022-02-13T13:14:15

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# 实现 `TemporalAdjuster`接口

我们还可以通过实现 TemporalAdjuster 接口来创建时间调整器

import java.time.LocalDate;
import java.time.temporal.ChronoField;
import java.time.temporal.Temporal;
import java.time.temporal.TemporalAdjuster;

class NextChristmas implements TemporalAdjuster {

    @Override
    public Temporal adjustInto(Temporal temporal) {

        return temporal.with(ChronoField.MONTH_OF_YEAR, 12)
                .with(ChronoField.DAY_OF_MONTH, 25);

    }
}

public class JavaCustomTemporalAdjusterEx2 {

    public static void main(String[] args) {

        var now = LocalDate.now();
        System.out.println("Today: " + now);

        var xmas = now.with(new NextChristmas());
        System.out.println("Next XMas: " + xmas);
    }
}