How to get and set specified time in java.time.Instant?

You have to interpret the Instant at some time zone to get ZonedDateTime. As an Instant measures the ellapsed seconds and nano seconds from epoch 1970-01-01T00:00:00Z you should use UTC to get the same time as the Instant would print. (Z ≙ Zulu Time ≙ UTC)

Getting the time

Instant instant;

// get overall time
LocalTime time = instant.atZone(ZoneOffset.UTC).toLocalTime();
// get hour
int hour = instant.atZone(ZoneOffset.UTC).getHour();
// get minute
int minute = instant.atZone(ZoneOffset.UTC).getMinute();
// get second
int second = instant.atZone(ZoneOffset.UTC).getSecond();
// get nano
int nano = instant.atZone(ZoneOffset.UTC).getNano();

There are also methods to get days, month and year (getX).

Setting the time

Instants are immutable so you can only “set” the time by creating a copy of your instant with the given time change.

instant = instant.atZone(ZoneOffset.UTC)
        .withHour(hour)
        .withMinute(minute)
        .withSecond(second)
        .withNano(nano)
        .toInstant();

There are also methods to alter days, month and year (withX) as well as methods to add (plusX) or subtract (minusX) time or date values.

To set the time to a value given as a string use: .with(LocalTime.parse("12:45:30"))