실제 애플리케이션에서 DB 트랜잭션을 사용해서 계좌이체 같이 원자성이 중요한 비즈니스 로직을 어떻게 구현하는지 알아봅시다.

먼저 트랜잭션 없이 단순하게 계좌이체 비즈니스 로직만 구현해보겠습니다.

MemberServiceV1

@RequiredArgsConstructor
public class MemberServiceV1 {

    private final MemberRepositoryV1 memberRepository;

		//...1
    public void accountTransfer(String fromId, String toId, int money) throws SQLException {
        Member fromMember = memberRepository.findById(fromId);
        Member toMember = memberRepository.findById(toId);

				//...2
        memberRepository.update(fromId, fromMember.getMoney() - money);
        validation(toMember);
		    //...3
        memberRepository.update(toId, toMember.getMoney() + money);
    }

    private void validation(Member toMember) {
				//...4
        if (toMember.getMemberId().equals("ex")) {
            throw new IllegalStateException("이체중 예외 발생");
        }
    }

}
  1. throw SQLException
  2. fromId 회원의 돈을 money 만큼 감소시킵니다. → UPDATE SQL 실행
  3. toId 회원의 돈을 money 만큼 증가시킵니다. → UPDATE SQL 실행
  4. 예외 상황을 테스트해보기 위해 toId 가 "ex" 인 경우 예외를 발생시킵니다.

formId 의 회원을 조회해서 toId 의 회원에게 money 만큼의 돈을 계좌이체 하는 로직입니다.

MemberServiceV1Test - 정상이체 - accountTransfer()

/**
 * 기본 동작, 트랜잭션이 없어서 문제 발생
 */
class MemberServiceV1Test {

    public static final String MEMBER_A = "memberA";
    public static final String MEMBER_B = "memberB";
    public static final String MEMBER_EX = "ex";

    private MemberRepositoryV1 memberRepository;
    private MemberServiceV1 memberService;

    @BeforeEach
    void before() {
		    //...1
        DriverManagerDataSource dataSource = new DriverManagerDataSource(URL, USERNAME, PASSWORD);
        memberRepository = new MemberRepositoryV1(dataSource);
        memberService = new MemberServiceV1(memberRepository);
    }

    @Test
    @DisplayName("정상 이체")
    void accountTransfer() throws SQLException {
        //given
        Member memberA = new Member(MEMBER_A, 10000);
        Member memberB = new Member(MEMBER_B, 10000);
        memberRepository.save(memberA);
        memberRepository.save(memberB);

        //when
        memberService.accountTransfer(memberA.getMemberId(), memberB.getMemberId(), 2000);

        //then
        Member findMemberA = memberRepository.findById(memberA.getMemberId());
        Member findMemberB = memberRepository.findById(memberB.getMemberId());
        assertThat(findMemberA.getMoney()).isEqualTo(8000);
        assertThat(findMemberB.getMoney()).isEqualTo(12000);
    }

}
  1. DriverManagerDataSource
  2. @BeforeEach