LocalDate无法用“YYYY”解析“WW”

Question

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyyw");
java.time.LocalDate startDate = java.time.LocalDate.parse("201710", formatter);
System.out.println(startDate);

java.time.format.DateTimeParseException: Text '201710' could not be parsed at index 0   

之后，我需要从LocalDate对象获得一周的第一天和最后一天。例如“201710”-05.03 12.03（每周第一天需为星期日）。

Answer 1

@Kayaman的公认答案是不正确的，因为您不能混合标准日期表示（使用yyyy=年份）和周日期表示（使用ww=周的周）。标准日历年和以周为基础的年之间微妙的差异在日历年的开始或结束时是相关的。结论：不要用符号“Y”，而要用符号“Y”。输入“201501”的反例：

正解

DateTimeFormatter formatter =
    new DateTimeFormatterBuilder()
    .appendValue(WeekFields.ISO.weekBasedYear(), 4)
    .appendValue(WeekFields.ISO.weekOfWeekBasedYear(), 2)
    .parseDefaulting(ChronoField.DAY_OF_WEEK, 1)
    .toFormatter();
LocalDate startDate = LocalDate.parse("201501", formatter);
System.out.println(startDate); // 2014-12-29

基于@Kayaman的提议：

DateTimeFormatter dtf =
    new DateTimeFormatterBuilder()
    .appendValue(ChronoField.YEAR, 4)
    .appendValue(ChronoField.ALIGNED_WEEK_OF_YEAR, 2)
    .parseDefaulting(WeekFields.ISO.dayOfWeek(), 1)
    .toFormatter();
System.out.println(LocalDate.parse("201501", dtf)); // 2015-01-05 (wrong)

    ChronoFormatter<CalendarWeek> cf =
        ChronoFormatter.ofPattern(
            "YYYYww",
            PatternType.CLDR,
            Locale.ROOT,
            CalendarWeek.chronology()
        );
    CalendarWeek cw = cf.parse("201501");
    System.out.println(cw); // 2015-W01
    System.out.println(cw.at(Weekday.MONDAY)); // 2014-12-29