회원 리포지토리, 도메인을 활용하여 실제 비즈니스 로직을 작성 1. service 패키지, MemberService 클래스 작성 package hello.hellospring.service; import hello.hellospring.domain.Member; import hello.hellospring.repository.MemberRepository; import hello.hellospring.repository.MemoryMemberRepository; import java.util.Optional; public class MemberService { private final MemberRepository memberRepository = new MemoryMemberRepository(); /..