Parse period/duration string literal into Period/Duration instance in Java

Question

I would like to parse any duration/period string literal (in the format shown in the examples below) into a Period/Duration instance in Java.

By duration/period, I mean an amount of time that contains both date-based and time-based quantities. In Java, Duration alone only works for time-based quantities like seconds, minutes, and hours, while Period alone only works for date-based quantities like years, months, and days.

The string to parse won't always contain all quantities.

Examples:

• 29 days 23 hours 59 minutes 20 seconds
• 4 years 10 months 10 seconds
• 10 days 9 minutes
• 1 month

How would I do that, if possible?

Answer 1

The ThreeTen Extra library seems like a good solution, but in my case I rather not include a large library just for the privilege of using a class that basically is a simple wrapper around java.time.Duration and java.time.Period (though in threeten's case it is probably a wrapper around their versions of Duration and Period - which I encountered and mostly find annoying).

So I wrote this replacement (here by posted under CC0 and/or whatever SO pretends they can force people to license their copyrighted content under):

import java.time.Duration;
import java.time.Instant;
import java.time.Period;

/**
 * Copyright Oded Arbel <oded@geek.co.il>
 * Licensed under [CC0](https://creativecommons.org/public-domain/cc0/)
 */
public class PeriodDuration {
    public static final ZoneId ZONE_UTC = ZoneId.ofOffset("", ZoneOffset.UTC);
    private Period period;
    private Duration duration;
    
    private PeriodDuration(Period period, Duration duration) {
        this.period = period;
        this.duration = duration;
    }

    public static PeriodDuration parse(String iso8601period) {
        var val = iso8601period.toLowerCase().startsWith("p") ? iso8601period.substring(1) : iso8601period;
        var parts = val.split("T",2);
        return new PeriodDuration(
                parts[0].isEmpty() ? Period.ZERO : Period.parse("P" + parts[0]),
                parts.length < 2 || parts[1].isEmpty() ? Duration.ZERO : Duration.parse("PT" + parts[1]));
    }
    
    @Override
    public String toString() {
        return period.toString() + "T" + duration.toString().split("T")[1];
    }
    
    public Period getPeriod() {
        return period;
    }
    
    public Duration getDuration() {
        return duration;
    }
    
    public Instant addTo(Instant time) {
        return time.atZone(ZONE_UTC).plus(period).plus(duration).toInstant();
    }
    
    public Instant substractFrom(Instant time) {
        return time.atZone(ZONE_UTC).minus(period).minus(duration).toInstant();
    }
}

I did not review any ThreeTen code - so this implementation may be missing a lot of features and/or doing things wrong - YMMV.