如何找到任意日期的最近工作日？

Question

有没有一种优雅的方法可以使用JodaTime查找给定日期的星期几？我最初以为setCopy()会是这样,但这会把这一天设定为同一周的特定日期.因此,如果ld是2011-11-27和day是"星期一",则以下函数返回2011-11-21,而不是2011-11-28我想要的.

    // Note that "day" can be _any_ day of the week, not just weekdays.
    LocalDate getNearestDayOfWeek(LocalDate ld, String day) {
        return ld.dayOfWeek().setCopy(day);
    }

各种输入的所需输出:

2011-12-04, Monday    => 2011-12-05
2011-12-04, Tuesday   => 2011-12-06
2011-12-04, Wednesday => 2011-12-07
2011-12-04, Thursday  => 2011-12-01
2011-12-04, Friday    => 2011-12-02
2011-12-04, Saturday  => 2011-12-03
2011-12-04, Sunday    => 2011-12-04

2011-12-05, Monday    => 2011-12-05
2011-12-05, Tuesday   => 2011-12-06
2011-12-05, Wednesday => 2011-12-07
2011-12-05, Thursday  => 2011-12-08
2011-12-05, Friday    => 2011-12-02
2011-12-05, Saturday  => 2011-12-03
2011-12-05, Sunday    => 2011-12-04

下面是我提出的解决方案,它适用于我当前情况下的特定约束,但我很乐意帮助找到一个始终有效的完全通用的解决方案.

    LocalDate getNearestDayOfWeek(LocalDate ld, String day) {
        LocalDate target = ld.dayOfWeek().setCopy(day);
        if (ld.getDayOfWeek() > DateTimeConstants.SATURDAY) {
            target = target.plusWeeks(1);
        }
        return target;
    }

Answer 1

在Jodatime中,这种事情应该是三行或四行:

   /** Given a reference LocalDate and a day of week, eg DateTimeConstants.MONDAY 
       Returns the nearest date with that day of week */
   public static LocalDate getNearestDayOfWeek(LocalDate t0,int dow) {
        LocalDate t1 = t0.withDayOfWeek(dow);
        LocalDate t2 = t1.isBefore(t0) ? t1.plusWeeks(1) : t1.minusWeeks(1);
        return  Math.abs(Days.daysBetween(t1, t0).getDays()) < 
                Math.abs(Days.daysBetween(t2, t0).getDays()) ? t1 : t2;
   }

或者更紧凑,更高效:

public static LocalDate getNearestDayOfWeek(LocalDate t0, int dow) {
    LocalDate t1 = t0.withDayOfWeek(dow);
    if (t1.isBefore(t0.minusDays(3)))       return t1.plusWeeks(1);
    else if (t1.isAfter(t0.plusDays(3)))    return t1.minusWeeks(1);
    else return t1;
}

如果你想以星期几的形式传递星期几:

public static LocalDate getNearestDayOfWeek(LocalDate t0, String dow) {
    return getNearestDayOfWeek(t0,t0.dayOfWeek().setCopy(dow).getDayOfWeek());
}

例:

    // prints 2011-11-28
   public static  void  main(String[] args) throws Exception {
        LocalDate today = new LocalDate(2011,11,27);
        int dow = DateTimeConstants.MONDAY;
        System.out.println(getNearestDayOfWeek(today ,dow ));
   }