Java 8 example for if else with Optional

Question

I have a method which returns Optional. Basically, it gets value from DB and if the value from DB is present and if the value is before 20 years, it returns currentDate-20 years or else return as it is.

Optional<Instant> getJoinDate(final Instant instant) {

        final Optional<Employee> joinTime = empService.retrieveById(1);

        if (joinTime.isPresent()) {

            final Instant joinDate = joinTime.get().getJoinTime().toInstant();

            if (joinDate.isBefore(instant.minus(20,ChronoUnit.YEARS))) {
                return Optional.of(instant.minus(20, ChronoUnit.YEARS));
            }
            else {
                return Optional.of(joinDate);
            }
        }

        return Optional.empty();
    }

Is there any simple way to do this with Java 8 without if else?

Thanks

Eran · Accepted Answer · 2017-11-14 14:21:21Z

You can use flatMap:

Optional<Instant> getJoinDate(final Instant instant) {
    final Optional<Employee> joinTime = empService.retrieveById(1);
    return joinTime.flatMap (emp -> {
        final Instant joinDate = emp.getJoinTime().toInstant();
        if (joinDate.isBefore(instant.minus(20,ChronoUnit.YEARS))) {
            return Optional.of(instant.minus(20, ChronoUnit.YEARS));
        }
        else {
            return Optional.of(joinDate);
        }
    });
}

of course you can replace the inner if-else with ternary conditional expression:

Optional<Instant> getJoinDate(final Instant instant) {
    final Optional<Employee> joinTime = empService.retrieveById(1);
    return joinTime.flatMap (emp -> {
        final Instant joinDate = emp.getJoinTime().toInstant();
        return joinDate.isBefore(instant.minus(20,ChronoUnit.YEARS)) ?
            Optional.of(instant.minus(20, ChronoUnit.YEARS)) :
            Optional.of(joinDate);
    });
}

or even shorter:

Optional<Instant> getJoinDate(final Instant instant) {
    return empService.retrieveById(1).flatMap (emp -> 
            emp.getJoinTime().toInstant().isBefore(instant.minus(20,ChronoUnit.YEARS)) ?
            Optional.of(instant.minus(20, ChronoUnit.YEARS)) :
            Optional.of(emp.getJoinTime().toInstant()));
}

However, this has the disadvantage of calling emp.getJoinTime().toInstant() twice.

Robert Bräutigam · Accepted Answer · 2017-11-14 14:55:17Z

1

If I understand your code correctly, this is it:

Optional<Instant> getJoinDate(Instant instant) {
    Instant cap = instant.minus(20,ChronoUnit.YEARS)
    return empService.retrieveById(1)
        .map(employee -> employee.getJoinTime().getInstant())
        .map(joinInstant -> joinInstant.before(cap)?cap:joinInstant);
}

answered Nov 14, 2017 at 14:55

Robert Bräutigam

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