如何从一个日期获得零售日历周(4-5-4)

Question

我需要从日期中获得4-5-4日历周。对于4-5-4零售日历，Java中有像格鲁吉亚日历这样的实用工具吗？如果没有，我如何创建一个？所有的逻辑都需要什么？什么是第53周，如果是飞跃年？

例如，如果我传递一个日期(DD-MM-YYY) 04-03-2018作为输入，我应该得到March Week 1作为输出。或者，如果我给01-04-2018作为输入，我应该得到March Week 5作为输出。

请帮助我提供一种方法来构建这个实用程序。

Answer 1

下面的课应该这样做：

public class NrfMonthWeek {

    public static NrfMonthWeek getWeek(LocalDate date) {
        // Determine NRF calendar year.
        // The year begins on the Sunday in the interval Jan 29 through Feb 4.
        LocalDate firstDayOfNrfYear = date.with(MonthDay.of(Month.JANUARY, 29))
                .with(TemporalAdjusters.nextOrSame(DayOfWeek.SUNDAY));
        if (date.isBefore(firstDayOfNrfYear)) { // previous NRF year
            firstDayOfNrfYear = date.minusYears(1)
                    .with(MonthDay.of(Month.JANUARY, 29))
                    .with(TemporalAdjusters.nextOrSame(DayOfWeek.SUNDAY));
        }
        // 1-based week of NRF year
        int weekOfNrfYear = (int) ChronoUnit.WEEKS.between(firstDayOfNrfYear, date) + 1;
        assert 1 <= weekOfNrfYear && weekOfNrfYear <= 53 : weekOfNrfYear;
        YearMonth firstMonthOfNrfYear = YearMonth.from(firstDayOfNrfYear)
                .with(Month.FEBRUARY);
        if (weekOfNrfYear == 53) {
            // Special case: the last week of a 53 weeks year belongs to
            // the last month, January; this makes it a 5 weeks month.
            return new NrfMonthWeek(firstMonthOfNrfYear.plusMonths(11), 5);
        } else {
            // 1-based month of NRF year (1 = February through 12 = January).
            // A little math trickery to make the 4-5-4 pattern real.
            int monthOfNrfYear = (weekOfNrfYear * 3 + 11) / 13;
            // Number of weeks before the NRF month: 0 for February, 4 for March, 9 for April, etc.
            int weeksBeforeMonth = (monthOfNrfYear * 13 - 12) / 3;
            int weekOfMonth = weekOfNrfYear - weeksBeforeMonth;
            return new NrfMonthWeek(
                    firstMonthOfNrfYear.plusMonths(monthOfNrfYear - 1), weekOfMonth);
        }
    }

    private YearMonth month;
    /** 1 through 5 */
    private int weekOfMonth;

    public NrfMonthWeek(YearMonth month, int weekOfMonth) {
        this.month = Objects.requireNonNull(month);
        if (weekOfMonth < 1 || weekOfMonth > 5) {
            throw new IllegalArgumentException("Incorrect week number " + weekOfMonth);
        }
        this.weekOfMonth = weekOfMonth;
    }

    @Override
    public String toString() {
        return month.getMonth().getDisplayName(TextStyle.FULL, Locale.US)
                + " Week " + weekOfMonth;
    }
}

我们试试看。在这里，我将两个日期从您的问题传递给getWeek方法：

    System.out.println(NrfMonthWeek.getWeek(LocalDate.of(2018, Month.MARCH, 4)));
    System.out.println(NrfMonthWeek.getWeek(LocalDate.of(2018, Month.APRIL, 1)));

这将打印所需的内容：

March Week 1
March Week 5

虽然只打印月份和周，但是从getWeek返回的对象中也包含了年份。

计算月和月周的公式是神秘的.我并没有很好的理由来解释它们的作用，尽管这样的论点可能是可以建立起来的。我已经用所有相关的价值观测试过它们，您也可以这样做。除此之外，使用java.time (现代java.time和time )并不是太糟糕。

如果是我，我将在NrfMonthWeek构造函数中进行更好的验证，只允许在可能有5周的月份中的第5周。我把这个留给你。我会进行相当彻底的单元测试。

请检查我的理解是否与您的理解一致:如果我从示例日历中正确地理解了Bourque与在他的回答中的链接，NRF 4-5-4年从2月开始。每周从周日开始，一年中的第一周是包含至少4天2月的第一周。换句话说，包含2月4日的那一周。换句话说，从1月29日到2月4日间隔的一个星期日开始的一周。三月、六月、九月和十二月总是有五个星期。如果是53周，1月份也有5周。

Answer 2

没有内置的支持

现代java.time类和遗留日期时类(Date/Calendar)都不直接支持全国零售联合会4-5-4日历。

实现Chronology

我怀疑解决这个问题的最好方法是为Chronology框架实现一个java.time。

Java 8和更高版本捆绑了五个实现(HijrahChronology、IsoChronology、JapaneseChronology、MinguoChronology、ThaiBuddhistChronology)。它们的源代码可以在OpenJDK项目中获得。

http://www.threeten.org/threeten-extra/项目提供十多个年表 (AccountingChronology、BritishCutoverChronology、CopticChronology、DiscordianChronology、EthiopicChronology、InternationalFixedChronology、JulianChronology、< code >D19、Symmetry010Chronology、Symmetry454Chronology)，源代码可能会有所帮助。