Period of weeks to string with weeks instead of days only - kotlin

Question

var period = Period.ofWeeks(2)
println("period of two weeks: $period")
gives
period of two weeks: P14D
Unfortunately for my purpose I need P2W as output, so directly the weeks instead of weeks converted to days. Is there any elegant way to do this, besides building my Period string manually?

Answer 1

Your observation is true. java.time.Period does not really conserve the week value but automatically converts it to days - already in the factory method during construction. Reason is that a Period only has days and months/years as inner state.
Possible workarounds or alternatives in the order of increasing complexity and count of features:
You write your own class implementing the interface java.time.temporal.TemporalAmount with weeks as inner state.
You use the small library threeten-extra which offers the class Weeks. But be aware of the odd style of printing negative durations like P-2W instead of -P2W. Example:
Weeks w1 = Weeks.of(2);
Weeks w2 = Weeks.parse("P2W");
System.out.println(w1.toString()); // P2W
System.out.println(w2.toString()); // P2W
Or you use my library Time4J which offers the class net.time4j.Duration. This class does not implement the interface TemporalAmount but offers a conversion method named toTemporalAmount(). Various normalization features and formatting (ISO, via patterns and via net.time4j.PrettyTime) and parsing (ISO and via patterns) capabilities are offered, too. Example:
Duration<CalendarUnit> d1 = Duration.of(2, CalendarUnit.WEEKS);
Duration<IsoDateUnit> d2 = Duration.parseWeekBasedPeriod("P2W"); // also for week-based-years
System.out.println(d1.toString()); // P2W
System.out.println(PrettyTime.of(Locale.US).print(d2); // 2 weeks
As extra, the same library also offers the class net.time4j.range.Weeks as simplified week-only duation.

Answer 2

The Period toString method only handles Day, Month and Year.
as you can see below is toString() method from class java.time.Period.
So Unfortunately I think you need to create it yourself.
/**
* Outputs this period as a {#code String}, such as {#code P6Y3M1D}.
* <p>
* The output will be in the ISO-8601 period format.
* A zero period will be represented as zero days, 'P0D'.
*
* #return a string representation of this period, not null
*/
#Override
public String toString() {
if (this == ZERO) {
return "P0D";
} else {
StringBuilder buf = new StringBuilder();
buf.append('P');
if (years != 0) {
buf.append(years).append('Y');
}
if (months != 0) {
buf.append(months).append('M');
}
if (days != 0) {
buf.append(days).append('D');
}
return buf.toString();
}
}