In java8, I would use the Instant class which is already in UTC and is convenient to work with.
import java.time.Instant;
Instant ins = Instant.now();
long ts = ins.toEpochMilli();
Instant ins2 = Instant.ofEpochMilli(ts)
Alternatively, you can use the following:
import java.time.*;
Instant ins = Instant.now();
OffsetDateTime odt = ins.atOffset(ZoneOffset.UTC);
ZonedDateTime zdt = ins.atZone(ZoneId.of("UTC"));
Back to Instant
Instant ins4 = Instant.from(odt);