如何在给定的本地日期后获得下周五13号

Question

我需要使用LocalDate获得给定日期后的下周五13号。

如何实施？

Answer 1

您可以使用IntStream迭代几天：

public static LocalDate findFridayThirteen(LocalDate fromDate) {
    return IntStream.iterate(0, i -> i + 1)
            .mapToObj(fromDate::plusDays)
            .filter(date -> date.getDayOfWeek() == DayOfWeek.FRIDAY 
                    && date.getDayOfMonth() == 13)
            .findFirst()
            .orElseThrow();
}

或者，您只能在周五重复：

public static LocalDate findFridayThirteen2(LocalDate fromDate) {
    LocalDate nextFriday = fromDate.with(
            TemporalAdjusters.nextOrSame(DayOfWeek.FRIDAY));
    return IntStream.iterate(0, i -> i + 7)
            .mapToObj(nextFriday::plusDays)
            .filter(date -> date.getDayOfMonth() == 13)
            .findFirst()
            .orElseThrow();
}  

或者，您可以只迭代每个月的13次：

public static LocalDate findFridayThirteen3(LocalDate fromDate) {
    LocalDate nextThirteen = fromDate.getDayOfMonth() > 13 
            ? fromDate.withDayOfMonth(13).plusMonths(1) 
            : fromDate.withDayOfMonth(13);
    return IntStream.iterate(0, i -> i + 1)
            .mapToObj(nextThirteen::plusMonths)
            .filter(date -> date.getDayOfWeek() == DayOfWeek.FRIDAY)
            .findFirst()
            .orElseThrow();
}  

测试：

LocalDate date = LocalDate.of(2022, 1, 1);

LocalDate friday13 = findFridayThirteen(date);

DateTimeFormatter formatter = DateTimeFormatter
        .ofLocalizedDate(FormatStyle.FULL);

System.out.println(friday13.format(formatter));

输出：

Friday, May 13, 2022

Answer 2

    public static void main(String[] args) {
    boolean is13Friday = false;
    LocalDate nextFriday = LocalDate.now();
    while (!is13Friday) {
        nextFriday = getNextFriday(nextFriday);
        is13Friday = is13Friday(nextFriday);
    }
    System.out.println(nextFriday);

}

public static LocalDate getNextFriday(LocalDate d) {
    return d.with(TemporalAdjusters.next(DayOfWeek.FRIDAY));
}

public static boolean is13Friday(LocalDate d) {
    return d.getDayOfMonth() == 13;
}

Answer 3

只需在LocalDate中添加7天，即可获得预期的日期：

例如：

 LocalDate today = LocalDate.now();

 //tomorrow
 LocalDate tomorrow = today.plusDays(1);

 // next week day
 LocalDate nextWeekDay= today.plusDays(7);

或者通过这个：

today.with(TemporalAdjusters.next(DayOfWeek.FRIDAY));