OffsetDateTimeToMillisecond

import java.time.OffsetDateTime;
import java.time.ZoneOffset;

public class CodeTest {
    public static void main(String[] args) {
        // https://currentmillis.com
        // https://perfectacle.github.io/2018/09/26/java8-date-time/
        OffsetDateTime offsetDateTime = OffsetDateTime.of(2019, 12, 2, 0, 0, 0, 0, ZoneOffset.UTC);
        System.out.println(offsetDateTime.toInstant().toEpochMilli());
    }
}