Get duration in microseconds

I wouldn’t use the java.time API for such a task, as you can simply use

long microseconds = TimeUnit.SECONDS.toMicros(2);

from the concurrency API which works since Java 5.

However, if you have an already existing Duration instance or any other reason to insist on using the java.time API, you can use

Duration existingDuration = Duration.ofSeconds(2);
long microseconds = existingDuration.dividedBy(ChronoUnit.MICROS.getDuration());

^{Requires Java 9 or newer}

For Java 8, there seems to be indeed no nicer way than existingDuration.toNanos() / 1000 or combine the two APIs like TimeUnit.NANOSECONDS.toMicros(existingDuration.toNanos()).

Based on Holger answer, my favorite would be:

final long microseconds = TimeUnit.NANOSECONDS.toMicros(twoSeconds.toNanos())