findMembers() { return memberRepository.findAll(); } public Optional findOne(Long memberId) { return memberRepository.findById(memberId); } }"> findMembers() { return memberRepository.findAll(); } public Optional findOne(Long memberId) { return memberRepository.findById(memberId); } }"> findMembers() { return memberRepository.findAll(); } public Optional findOne(Long memberId) { return memberRepository.findById(memberId); } }"> 
package hello.hellospring.service;
 import hello.hellospring.domain.Member;
 import hello.hellospring.repository.MemberRepository;
 
  import java.util.List;
 import java.util.Optional;
 public class MemberService {
     private final MemberRepository memberRepository = new
 MemoryMemberRepository();
/**
* 회원가입 */
     public Long join(Member member) {
validateDuplicateMember(member); //중복 회원 검증 memberRepository.save(member);
return member.getId();
}
     private void validateDuplicateMember(Member member) {
         memberRepository.findByName(member.getName())
.ifPresent(m -> {
throw new IllegalStateException("이미 존재하는 회원입니다.");
}); }
/**
*전체 회원 조회 */
     public List<Member> findMembers() {
         return memberRepository.findAll();
}
     public Optional<Member> findOne(Long memberId) {
         return memberRepository.findById(memberId);
} }