time - Java 8 Instant.now() with nanosecond resolution?

Question

Java 8's java.time.Instant stores in "nanosecond resolution", but using Instant.now() only provides millisecond resolution...

Instant instant = Instant.now();
System.out.println(instant);
System.out.println(instant.getNano());

Result...

2013-12-19T18:22:39.639Z
639000000

How can I get an Instant whose value is 'now', but with nanosecond resolution?

Answer 1

While default Java8 clock does not provide nanoseconds resolution, you can combine it with Java ability to measure time differences with nanoseconds resolution, thus creating an actual nanosecond-capable clock.

public class NanoClock extends Clock
{
    private final Clock clock;

    private final long initialNanos;

    private final Instant initialInstant;

    public NanoClock()
    {
        this(Clock.systemUTC());
    }

    public NanoClock(final Clock clock)
    {
        this.clock = clock;
        initialInstant = clock.instant();
        initialNanos = getSystemNanos();
    }

    @Override
    public ZoneId getZone()
    {
        return clock.getZone();
    }

    @Override
    public Instant instant()
    {
        return initialInstant.plusNanos(getSystemNanos() - initialNanos);
    }

    @Override
    public Clock withZone(final ZoneId zone)
    {
        return new NanoClock(clock.withZone(zone));
    }

    private long getSystemNanos()
    {
        return System.nanoTime();
    }
}

Using it is straightforward: just provide extra parameter to Instant.now(), or call Clock.instant() directly:

    final Clock clock = new NanoClock();   
    final Instant instant = Instant.now(clock);
    System.out.println(instant);
    System.out.println(instant.getNano());

Although this solution might work even if you re-create NanoClock instances every time, it's always better to stick with a stored clock initialized early in your code, then used wherever it's needed.