java LocalDateTime OffsetDateTime 의 호환

자바로 구성된 애플리케이션에서 자주 발생하는 문제중 LocalDateTime 과 OffsetDateTime 간의 컨버팅이 필요할 때가 있다. 

OffsetDateTime ➡️ LocalDateTime

@Test
public void offsetToLocalTest() {
    DateTimeFormatter formatter1 = DateTimeFormatter.ISO_OFFSET_DATE_TIME;
    DateTimeFormatter formatter2 = DateTimeFormatter.ISO_DATE_TIME;
    TemporalAccessor input = formatter1.parse("2023-03-13T01:00:00+01:00");

    OffsetDateTime offset = OffsetDateTime.from(input);
    LocalDateTime local = offset
            .atZoneSameInstant(ZoneId.systemDefault())
            .toLocalDateTime();

    System.out.println("Offset: " + formatter2.format(offset));
    System.out.println("Local : " + formatter2.format(local));

    Date offDate = Date.from(offset.toInstant());
    Date localDate = Date.from(local.atZone(ZoneId.systemDefault()).toInstant());

    Assertions.assertThat(offDate).isEqualTo(localDate);
}

LocalDateTime ➡️ OffsetDateTime

@Test
public void localToOffsetTest() {
    DateTimeFormatter formatter1 = DateTimeFormatter.ISO_OFFSET_DATE_TIME;
    DateTimeFormatter formatter2 = DateTimeFormatter.ISO_DATE_TIME;
    TemporalAccessor input = formatter2.parse("2023-03-13T09:00:00");
    LocalDateTime local = LocalDateTime.from(input);
    OffsetDateTime offset = local.atZone(ZoneId.systemDefault()).toOffsetDateTime();
    offset = offset.withOffsetSameInstant(ZoneOffset.UTC);

    System.out.println("Local : " + formatter2.format(local));
    System.out.println("Offset: " + formatter2.format(offset));

    Date offDate = Date.from(offset.toInstant());
    Date localDate = Date.from(local.atZone(ZoneId.systemDefault()).toInstant());

    Assertions.assertThat(offDate).isEqualTo(localDate);
}

전체 소스 코드

import org.assertj.core.api.Assertions;
import org.junit.jupiter.api.Test;

import java.time.LocalDateTime;
import java.time.OffsetDateTime;
import java.time.ZoneId;
import java.time.ZoneOffset;
import java.time.format.DateTimeFormatter;
import java.time.temporal.TemporalAccessor;
import java.util.Date;

public class DateTimeTest {

    @Test
    public void offsetToLocalTest() {
        DateTimeFormatter formatter1 = DateTimeFormatter.ISO_OFFSET_DATE_TIME;
        DateTimeFormatter formatter2 = DateTimeFormatter.ISO_DATE_TIME;
        TemporalAccessor input = formatter1.parse("2023-03-13T01:00:00+01:00");

        OffsetDateTime offset = OffsetDateTime.from(input);
        LocalDateTime local = offset
                .atZoneSameInstant(ZoneId.systemDefault())
                .toLocalDateTime();

        System.out.println("Offset: " + formatter2.format(offset));
        System.out.println("Local : " + formatter2.format(local));

        Date offDate = Date.from(offset.toInstant());
        Date localDate = Date.from(local.atZone(ZoneId.systemDefault()).toInstant());

        Assertions.assertThat(offDate).isEqualTo(localDate);
    }


    @Test
    public void localToOffsetTest() {
        DateTimeFormatter formatter1 = DateTimeFormatter.ISO_OFFSET_DATE_TIME;
        DateTimeFormatter formatter2 = DateTimeFormatter.ISO_DATE_TIME;
        TemporalAccessor input = formatter2.parse("2023-03-13T09:00:00");
        LocalDateTime local = LocalDateTime.from(input);
        OffsetDateTime offset = local.atZone(ZoneId.systemDefault()).toOffsetDateTime();
        offset = offset.withOffsetSameInstant(ZoneOffset.UTC);

        System.out.println("Local : " + formatter2.format(local));
        System.out.println("Offset: " + formatter2.format(offset));

        Date offDate = Date.from(offset.toInstant());
        Date localDate = Date.from(local.atZone(ZoneId.systemDefault()).toInstant());

        Assertions.assertThat(offDate).isEqualTo(localDate);
    }
}