How to properly use ThreeTenABP to get the time in milliseconds between two dates based on UTC

Question

I'm using this library I just discovered which is supposedly less heavier than Joda time for android and I said what the heck, let's use it. But now I'm struggling to find any good examples on the web about how to use it, besides these two methods I have:

// ZonedDateTime contains timezone information at the end
// For example, 2011-12-03T10:15:30+01:00[Europe/Paris]
public static ZonedDateTime getDate(String dateString) {
    return ZonedDateTime.parse(dateString).withZoneSameInstant(ZoneId.of("UTC"));
}

public static String formatDate(String format, String dateString) {
    return DateTimeFormatter.ofPattern(format).format(getDate(dateString));
}

So how can I get the difference between two dates with this library?

Answer 1

There are several options depending on what you require from the difference you obtain.

It’s easiest to find the difference measured in some time unit. Use ChronoUnit.between. For example:

    ZonedDateTime zdt1 = getDate("2011-12-03T10:15:30+01:00[Europe/Paris]");
    ZonedDateTime zdt2 = getDate("2017-11-23T23:43:45-05:00[America/New_York]");

    long diffYears = ChronoUnit.YEARS.between(zdt1, zdt2);
    System.out.println("Difference is " + diffYears + " years");

    long diffMilliseconds = ChronoUnit.MILLIS.between(zdt1, zdt2);
    System.out.println("Difference is " + diffMilliseconds + " ms");

This prints:

Difference is 5 years
Difference is 188594895000 ms

I am using your getDate method, so the format required is that of ZonedDateTime (modified from ISO 8601), for example 2011-12-03T10:15:30+01:00[Europe/Paris]. Seconds and fraction of second are optional, as is time zone ID in square brackets.

BTW you don’t need to convert to UTC before finding the difference. You will get the same result even if you leave out that conversion.

You may also get the difference in years, months and days. The Period class can give you this, but it cannot handle time of day, so convert to LocalDate first:

    Period diff = Period.between(zdt1.toLocalDate(), zdt2.toLocalDate());
    System.out.println("Difference is " + diff);

Difference is P5Y11M21D

The output means a period of 5 years 11 months 21 days. The syntax may feel a little strange at first, but is straightforward. It is defined by the ISO 8601 standard. In this case the time zone matters since it is never the same date in all time zones.

To get the difference in hours, minutes and seconds use the Duration class (I am introducing a new time since using Duration for nearly 6 years would be too atypical (though possible)).

    ZonedDateTime zdt3 = getDate("2017-11-24T18:45:00+01:00[Europe/Copenhagen]");
    Duration diff = Duration.between(zdt2, zdt3);
    System.out.println("Difference is " + diff);

Difference is PT13H1M15S

A period of 13 hours 1 minute 15 seconds. The T that you already know from 2011-12-03T10:15:30+01:00[Europe/Paris] here too separates the date part from the time part so you know that in this case 1M means 1 minute, not 1 month.