Get the weeknumber from a given date in Java FX

Question

I have a javafx.scene.control.DatePicker. I want to extract the (Locale) week number from the selected date. Until now i haven\'t found a solution and i prefer not to write

Answer 1

FX DatePicker is based on the new (to jdk8) Date/Time api - time to learn how-to use it (not entirely sure I found the shortest way, though - corrections welcome :-)

The picker's value is a LocalDate, which can be queried for certain TemporalFields. Locale-aware week-related fields are provided by the WeekFields class, f.i. weekOfYear:

DatePicker picker = new DatePicker();
picker.valueProperty().addListener((p, oldValue, newValue) -> {
    if (newValue == null) return;
    WeekFields fields = WeekFields.of(Locale.getDefault());

    // # may range from 0 ... 54 without overlapping the boundaries of calendar year
    int week = newValue.get(fields.weekOfYear());

    // # may range from 1 ... 53 with overlapping 
    int weekBased = newValue.get(fields.weekOfWeekBasedYear());

    LOG.info("week/Based " + week + "/" + weekBased);
});

To see the difference, choose f.i. January 2012 (in locales that start a week at Monday). Which one to actually use, depends on context - the picker itself uses weekOfYear (if showWeekNumbers is enabled)