TemporalAdjusters

- 日理万妓 2022-12-11 09:29 88阅读 0赞

Java8引入了新的日期、时间库--即java.time包，TemporalAdjuster类是其中之一。时间调节器，将一个时间调节成另外一个时间

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

有两种类等效的使用TemporalAdjuster的方式

//第一种
    temporal = thisAdjuster.adjustInto(temporal);
    //第二种
    temporal = temporal.with(thisAdjuster);

建议使用第二种，读起来更清晰。

TemporalAdjusters类包含一些标准的调节器。

比如：

*  查找每个月的第一天或最后一天

## ofDateAdjuster ##

//生成一个日期的调节器
        public static TemporalAdjuster ofDateAdjuster(UnaryOperator<LocalDate> dateBasedAdjuster) {
            Objects.requireNonNull(dateBasedAdjuster, "dateBasedAdjuster");
            return (temporal) -> {
                LocalDate input = LocalDate.from(temporal);
                LocalDate output = dateBasedAdjuster.apply(input);
                return temporal.with(output);
            };
        }

[官方文档][Link 1]

## firstDayOfMonth ##

返回每个月第一天的调节器

public static TemporalAdjuster firstDayOfMonth() {
            return (temporal) -> temporal.with(DAY_OF_MONTH, 1);
        }

## lastDayOfMonth ##

一个月的最后一天

public static TemporalAdjuster lastDayOfMonth() {
            return (temporal) -> temporal.with(DAY_OF_MONTH, temporal.range(DAY_OF_MONTH).getMaximum());
        }

## firstDayOfNextMonth ##

下个月的最后一天

public static TemporalAdjuster firstDayOfNextMonth() {
            return (temporal) -> temporal.with(DAY_OF_MONTH, 1).plus(1, MONTHS);
        }

## firstDayOfYear ##

一年的第一天

public static TemporalAdjuster firstDayOfYear() {
            return (temporal) -> temporal.with(DAY_OF_YEAR, 1);
        }

## lastDayOfYear ##

一年的最后一天

public static TemporalAdjuster lastDayOfYear() {
            return (temporal) -> temporal.with(DAY_OF_YEAR, temporal.range(DAY_OF_YEAR).getMaximum());
        }

## firstDayOfNextYear ##

下一年的第一天

public static TemporalAdjuster firstDayOfNextYear() {
            return (temporal) -> temporal.with(DAY_OF_YEAR, 1).plus(1, YEARS);
        }

## firstInMonth ##

某月的第一个星期几

public static TemporalAdjuster firstInMonth(DayOfWeek dayOfWeek) {
            return TemporalAdjusters.dayOfWeekInMonth(1, dayOfWeek);
        }

## lastInMonth ##

某月的最后一个星期几

public static TemporalAdjuster lastInMonth(DayOfWeek dayOfWeek) {
            return TemporalAdjusters.dayOfWeekInMonth(-1, dayOfWeek);
        }

## dayOfWeekInMonth ##

某月的第几个星期几

ordinal为正数，则从这个月的前面开始算，为负数，则倒着算

public static TemporalAdjuster dayOfWeekInMonth(int ordinal, DayOfWeek dayOfWeek) {
            Objects.requireNonNull(dayOfWeek, "dayOfWeek");
            int dowValue = dayOfWeek.getValue();
            if (ordinal >= 0) {
                return (temporal) -> {
                    Temporal temp = temporal.with(DAY_OF_MONTH, 1);
                    int curDow = temp.get(DAY_OF_WEEK);
                    int dowDiff = (dowValue - curDow + 7) % 7;
                    dowDiff += (ordinal - 1L) * 7L;  // safe from overflow
                    return temp.plus(dowDiff, DAYS);
                };
            } else {
                return (temporal) -> {
                    Temporal temp = temporal.with(DAY_OF_MONTH, temporal.range(DAY_OF_MONTH).getMaximum());
                    int curDow = temp.get(DAY_OF_WEEK);
                    int daysDiff = dowValue - curDow;
                    daysDiff = (daysDiff == 0 ? 0 : (daysDiff > 0 ? daysDiff - 7 : daysDiff));
                    daysDiff -= (-ordinal - 1L) * 7L;  // safe from overflow
                    return temp.plus(daysDiff, DAYS);
                };
            }
        }

例子：

public static void main(String[] args) {
    
            LocalDate localDate = LocalDate.now();
            // 当月的第一个星期日的日期
            localDate.with(TemporalAdjusters.firstInMonth(DayOfWeek.SUNDAY));
            System.out.println(localDate.with(TemporalAdjusters.firstInMonth(DayOfWeek.SUNDAY)));
            // 当月的第二个星期日的日期
            TemporalAdjuster temporalAdjuster = TemporalAdjusters.dayOfWeekInMonth(2, DayOfWeek.SUNDAY);
            System.out.println(localDate.with(temporalAdjuster));
    
            localDate.with(TemporalAdjusters.dayOfWeekInMonth(-1,DayOfWeek.SUNDAY));
            // 当月的最后一个星期日的日期
            System.out.println(localDate.with(TemporalAdjusters.dayOfWeekInMonth(-1,DayOfWeek.SUNDAY)));
            // 当月的倒数第二个星期日的日期
            System.out.println(localDate.with(TemporalAdjusters.dayOfWeekInMonth(-2,DayOfWeek.SUNDAY)));
    
    
        }

## next ##

*The input 2011-01-15 (a Saturday) for parameter (SATURDAY) will return 2011-01-22 (seven days later)*

下一个星期一是几月几号

public static TemporalAdjuster next(DayOfWeek dayOfWeek) {
            int dowValue = dayOfWeek.getValue();
            return (temporal) -> {
                int calDow = temporal.get(DAY_OF_WEEK);
                int daysDiff = calDow - dowValue;
                return temporal.plus(daysDiff >= 0 ? 7 - daysDiff : -daysDiff, DAYS);
            };
        }

## nextOrSame ##

The ISO calendar system behaves as follows:  
The input 2011-01-15 (a Saturday) for parameter (MONDAY) will return 2011-01-17 (two days later).  
The input 2011-01-15 (a Saturday) for parameter (WEDNESDAY) will return 2011-01-19 (four days later).  
The input 2011-01-15 (a Saturday) for parameter (SATURDAY) will return 2011-01-15 (same as input).

public static TemporalAdjuster nextOrSame(DayOfWeek dayOfWeek) {
            int dowValue = dayOfWeek.getValue();
            return (temporal) -> {
                int calDow = temporal.get(DAY_OF_WEEK);
                if (calDow == dowValue) {
                    return temporal;
                }
                int daysDiff = calDow - dowValue;
                return temporal.plus(daysDiff >= 0 ? 7 - daysDiff : -daysDiff, DAYS);
            };
        }

## previous ##

public static TemporalAdjuster previous(DayOfWeek dayOfWeek) {
            int dowValue = dayOfWeek.getValue();
            return (temporal) -> {
                int calDow = temporal.get(DAY_OF_WEEK);
                int daysDiff = dowValue - calDow;
                return temporal.minus(daysDiff >= 0 ? 7 - daysDiff : -daysDiff, DAYS);
            };
        }

##   previousOrSame ##

public static TemporalAdjuster previousOrSame(DayOfWeek dayOfWeek) {
            int dowValue = dayOfWeek.getValue();
            return (temporal) -> {
                int calDow = temporal.get(DAY_OF_WEEK);
                if (calDow == dowValue) {
                    return temporal;
                }
                int daysDiff = dowValue - calDow;
                return temporal.minus(daysDiff >= 0 ? 7 - daysDiff : -daysDiff, DAYS);
            };
        }

[Link 1]: https://docs.oracle.com/javase/8/docs/api/java/time/temporal/TemporalAdjusters.html