♻️ refactor: 회원 탈퇴 로직에 Observer 패턴 적용하여 서비스 간 결합도 완화

[문제]
- 기존의 회원 탈퇴(`withdraw`) 로직은 MemberService가 GroupCommandService, ScheduleCommandService 들을 직접 호출하는 구조
- 서비스 간의 의존성이 높아져 코드의 유연성과 확장성이 저하되는 문제 발생

[접근]
Spring의 ApplicationEventPublisher를 사용하여 Observer 패턴을 적용

[변경 사항]
- MemberWithdrawalEvent: 회원 탈퇴 시 발행할 이벤트를 정의
- MemberService: ApplicationEventPublisher를 주입받아, 회원 탈퇴가 발생하면 MemberWithdrawalEvent를 발행하도록 withdraw 메서드를 변경, GroupCommandService와 ScheduleCommandService에 대한 직접적인 의존성을 제거
- Group/ScheduleCommandService: @eventlistener 어노테이션을 사용하여 MemberWithdrawalEvent를 구독하는 메서드를 각 서비스에 추가, 각 서비스는 회원 탈퇴 이벤트를 감지하여 그룹 탈퇴 처리, 일정 관리자 위임 등 관련된 후속 작업을 독립적으로 수행

향후 회원 탈퇴 시 추가적인 작업이 필요할 경우 다른 서비스 코드의 수정 없이 새로운 리스너를 추가하는 것만으로 간단하게 확장할 수 있음

Author: leeseojun34

src/main/java/com/grepp/spring/app/model/group/service/GroupCommandService.java

@@ -17,6 +17,7 @@
 import com.grepp.spring.app.model.group.repository.GroupMemberCommandRepository;
 import com.grepp.spring.app.model.group.repository.GroupMemberRepository;
 import com.grepp.spring.app.model.member.entity.Member;
+import com.grepp.spring.app.model.member.event.MemberWithdrawalEvent;
 import com.grepp.spring.app.model.member.repository.MemberRepository;
 import com.grepp.spring.app.model.schedule.code.ScheduleRole;
 import com.grepp.spring.app.model.schedule.entity.Schedule;
@@ -38,6 +39,7 @@
 import java.util.Optional;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
+import org.springframework.context.event.EventListener;
 import org.springframework.security.core.Authentication;
 import org.springframework.security.core.context.SecurityContextHolder;
 import org.springframework.stereotype.Service;
@@ -432,6 +434,14 @@ private void findScheduleMembersOrThrow(ScheduleToGroupRequest request) {
         }
     }
 
+    // 회원 탈퇴 이벤트 리스너
+    @EventListener
+    @Transactional
+    public void handleMemberWithdrawal(MemberWithdrawalEvent event) {
+        Member member = event.getMember();
+        handleGroupWithdrawal(member);
+    }
+
     // 회원 탈퇴 중 그룹 관련 처리 메서드
     @Transactional
     public void handleGroupWithdrawal(Member member) {

src/main/java/com/grepp/spring/app/model/member/event/MemberWithdrawalEvent.java

@@ -0,0 +1,16 @@
+package com.grepp.spring.app.model.member.event;
+
+import com.grepp.spring.app.model.member.entity.Member;
+import lombok.Getter;
+import org.springframework.context.ApplicationEvent;
+
+@Getter
+public class MemberWithdrawalEvent extends ApplicationEvent {
+
+    private final Member member;
+
+    public MemberWithdrawalEvent(Object source, Member member) {
+        super(source);
+        this.member = member;
+    }
+}

src/main/java/com/grepp/spring/app/model/member/service/MemberService.java

@@ -5,6 +5,7 @@
 import com.grepp.spring.app.controller.api.member.payload.ModifyMemberInfoResponse;
 import com.grepp.spring.app.model.group.service.GroupCommandService;
 import com.grepp.spring.app.model.member.entity.Member;
+import com.grepp.spring.app.model.member.event.MemberWithdrawalEvent;
 import com.grepp.spring.app.model.member.repository.MemberRepository;
 import com.grepp.spring.app.model.schedule.service.ScheduleCommandService;
 import com.grepp.spring.infra.error.exceptions.mypage.MemberNotFoundException;
@@ -14,6 +15,7 @@
 import java.util.Optional;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
+import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.security.core.context.SecurityContextHolder;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
@@ -25,8 +27,7 @@ public class MemberService {
 
     private final MemberRepository memberRepository;
     private final AuthService authService;
-    private final GroupCommandService groupCommandService;
-    private final ScheduleCommandService scheduleCommandService;
+    private final ApplicationEventPublisher eventPublisher;
 
     public Optional<Member> findById(String userId) {
         return memberRepository.findById(userId);
@@ -75,14 +76,14 @@ public ModifyMemberInfoResponse modifyProfileImage(String userId) {
     public void withdraw(String userId, HttpServletResponse response, HttpServletRequest request) {
         Member member = memberRepository.findById(userId)
             .orElseThrow(() -> new MemberNotFoundException(MyPageErrorCode.MEMBER_NOT_FOUND));
-        // 1. 그룹 관련
-        groupCommandService.handleGroupWithdrawal(member);
-        // 2. 일정 관련
-        scheduleCommandService.handleScheduleWithdrawal(member);
-        // 3. 회원 탈퇴(삭제)
+
+        // 1. 회원 탈퇴 이벤트 발행
+        eventPublisher.publishEvent(new MemberWithdrawalEvent(this, member));
+
+        // 2. 회원 탈퇴(삭제)
         memberRepository.delete(member);
         log.info("회원 탈퇴가 완료되었습니다. 회원 ID: {}, 회원명: {}", member.getId(), member.getName());
-        // 4. 로그아웃 (토큰 무효화)
+        // 3. 로그아웃 (토큰 무효화)
         authService.logout(request, response); // 다른 서비스 참조. 괜찮은가 ?
         SecurityContextHolder.clearContext();
     }

src/main/java/com/grepp/spring/app/model/schedule/service/ScheduleCommandService.java

@@ -8,6 +8,7 @@
 import com.grepp.spring.app.controller.api.schedule.payload.response.CreateSchedulesResponse;
 import com.grepp.spring.app.model.event.entity.Event;
 import com.grepp.spring.app.model.member.entity.Member;
+import com.grepp.spring.app.model.member.event.MemberWithdrawalEvent;
 import com.grepp.spring.app.model.member.repository.MemberRepository;
 import com.grepp.spring.app.model.schedule.code.MeetingPlatform;
 import com.grepp.spring.app.model.schedule.code.ScheduleRole;
@@ -29,6 +30,7 @@
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.event.EventListener;
 import org.springframework.http.*;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
@@ -555,6 +557,14 @@ private Location saveSuggestedLocation(Schedule schedule, WriteSuggestedLocation
         return location;
     }
 
+    // 회원 탈퇴 이벤트 리스너
+    @EventListener
+    @Transactional
+    public void handleMemberWithdrawal(MemberWithdrawalEvent event) {
+        Member member = event.getMember();
+        handleScheduleWithdrawal(member);
+    }
+
     // 회원 탈퇴 중 일정 관련 처리 메서드
     @Transactional
     public void handleScheduleWithdrawal(Member member) {