feat: 채팅방 멤버 목록 조회 API 추가

src/main/java/gg/agit/konect/domain/chat/controller/ChatApi.java

@@ -16,13 +16,15 @@
 import gg.agit.konect.domain.chat.dto.ChatMessageSendRequest;
 import gg.agit.konect.domain.chat.dto.ChatMuteResponse;
 import gg.agit.konect.domain.chat.dto.ChatRoomCreateRequest;
+import gg.agit.konect.domain.chat.dto.ChatRoomMembersResponse;
 import gg.agit.konect.domain.chat.dto.ChatRoomNameUpdateRequest;
 import gg.agit.konect.domain.chat.dto.ChatRoomResponse;
 import gg.agit.konect.domain.chat.dto.ChatRoomsSummaryResponse;
 import gg.agit.konect.domain.chat.dto.ChatSearchResponse;
 import gg.agit.konect.domain.chat.enums.ChatInviteSortBy;
 import gg.agit.konect.global.auth.annotation.UserId;
 import io.swagger.v3.oas.annotations.Operation;
+import io.swagger.v3.oas.annotations.Parameter;
 import io.swagger.v3.oas.annotations.tags.Tag;
 import jakarta.validation.Valid;
 import jakarta.validation.constraints.Max;
@@ -267,4 +269,23 @@ ResponseEntity<ChatRoomResponse> createGroupChatRoom(
         @Valid @RequestBody ChatRoomCreateRequest.Group request,
         @UserId Integer userId
     );
+
+    @Operation(summary = "채팅방 멤버 목록 조회", description = """
+        ## 설명
+        - 특정 채팅방의 모든 멤버 목록을 조회합니다.
+
+        ## 로직
+        - 채팅방에 참여 중인 멤버만 조회할 수 있습니다.
+        - 나간 멤버(leftAt이 설정된 멤버)는 목록에 포함되지 않습니다.
+        - 각 멤버의 userId, 이름, 프로필 이미지, 방장 여부, 참여 시간을 반환합니다.
+
+        ## 에러
+        - FORBIDDEN_CHAT_ROOM_ACCESS (403): 채팅방에 접근할 권한이 없습니다.
+        - NOT_FOUND_CHAT_ROOM (404): 채팅방을 찾을 수 없습니다.
+        """)
+    @GetMapping("/rooms/{chatRoomId}/members")
+    ResponseEntity<ChatRoomMembersResponse> getChatRoomMembers(
+        @Parameter(description = "채팅방 ID") @PathVariable Integer chatRoomId,
+        @UserId Integer userId
+    );
 }

src/main/java/gg/agit/konect/domain/chat/controller/ChatController.java

@@ -2,6 +2,7 @@
 
 import org.springframework.http.ResponseEntity;
 import org.springframework.validation.annotation.Validated;
+import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.RequestMapping;
@@ -14,11 +15,13 @@
 import gg.agit.konect.domain.chat.dto.ChatMessageSendRequest;
 import gg.agit.konect.domain.chat.dto.ChatMuteResponse;
 import gg.agit.konect.domain.chat.dto.ChatRoomCreateRequest;
+import gg.agit.konect.domain.chat.dto.ChatRoomMembersResponse;
 import gg.agit.konect.domain.chat.dto.ChatRoomNameUpdateRequest;
 import gg.agit.konect.domain.chat.dto.ChatRoomResponse;
 import gg.agit.konect.domain.chat.dto.ChatRoomsSummaryResponse;
 import gg.agit.konect.domain.chat.dto.ChatSearchResponse;
 import gg.agit.konect.domain.chat.enums.ChatInviteSortBy;
+import gg.agit.konect.domain.chat.service.ChatRoomMembershipService;
 import gg.agit.konect.domain.chat.service.ChatService;
 import gg.agit.konect.global.auth.annotation.UserId;
 import jakarta.validation.Valid;
@@ -31,6 +34,7 @@
 public class ChatController implements ChatApi {
 
     private final ChatService chatService;
+    private final ChatRoomMembershipService chatRoomMembershipService;
 
     @Override
     public ResponseEntity<ChatRoomResponse> createOrGetChatRoom(
@@ -147,4 +151,13 @@ public ResponseEntity<ChatRoomResponse> createGroupChatRoom(
         ChatRoomResponse response = chatService.createGroupChatRoom(userId, request);
         return ResponseEntity.ok(response);
     }
+
+    @Override
+    @GetMapping("/rooms/{chatRoomId}/members")
+    public ResponseEntity<ChatRoomMembersResponse> getChatRoomMembers(
+        @PathVariable Integer chatRoomId,
+        @UserId Integer userId) {
+        ChatRoomMembersResponse response = chatRoomMembershipService.getChatRoomMembers(chatRoomId, userId);
+        return ResponseEntity.ok(response);
+    }
 }

src/main/java/gg/agit/konect/domain/chat/dto/ChatRoomMemberResponse.java

@@ -0,0 +1,12 @@
+package gg.agit.konect.domain.chat.dto;
+
+import java.time.LocalDateTime;
+
+public record ChatRoomMemberResponse(
+    Integer userId,
+    String name,
+    String profileImageUrl,
+    boolean isOwner,
+    LocalDateTime joinedAt
+) {
+}

src/main/java/gg/agit/konect/domain/chat/dto/ChatRoomMembersResponse.java

@@ -0,0 +1,8 @@
+package gg.agit.konect.domain.chat.dto;
+
+import java.util.List;
+
+public record ChatRoomMembersResponse(
+    List<ChatRoomMemberResponse> members
+) {
+}

src/main/java/gg/agit/konect/domain/chat/repository/ChatRoomMemberRepository.java

@@ -120,6 +120,27 @@ List<RoomUnreadCountProjection> countUnreadByRoomIdsAndUserId(
         @Param("userId") Integer userId
     );
 
+    @Query("""
+        SELECT COUNT(crm) > 0
+        FROM ChatRoomMember crm
+        WHERE crm.id.chatRoomId = :chatRoomId
+          AND crm.id.userId = :userId
+          AND crm.leftAt IS NULL
+        """)
+    boolean existsActiveByChatRoomIdAndUserId(
+        @Param("chatRoomId") Integer chatRoomId,
+        @Param("userId") Integer userId
+    );
+
+    @Query("""
+        SELECT crm
+        FROM ChatRoomMember crm
+        JOIN FETCH crm.user
+        WHERE crm.id.chatRoomId = :chatRoomId
+          AND crm.leftAt IS NULL
+        """)
+    List<ChatRoomMember> findActiveMembersByChatRoomId(@Param("chatRoomId") Integer chatRoomId);
+
     List<ChatRoomMember> saveAll(Iterable<ChatRoomMember> chatRoomMembers);
 
 }

src/main/java/gg/agit/konect/domain/chat/service/ChatRoomMembershipService.java

@@ -2,6 +2,7 @@
 
 import static gg.agit.konect.global.code.ApiResponseCode.FORBIDDEN_CHAT_ROOM_ACCESS;
 import static gg.agit.konect.global.code.ApiResponseCode.NOT_FOUND_CHAT_ROOM;
+import static gg.agit.konect.global.code.ApiResponseCode.NOT_FOUND_USER;
 
 import java.time.LocalDateTime;
 import java.util.List;
@@ -15,6 +16,8 @@
 
 import gg.agit.konect.domain.chat.model.ChatRoom;
 import gg.agit.konect.domain.chat.model.ChatRoomMember;
+import gg.agit.konect.domain.chat.dto.ChatRoomMemberResponse;
+import gg.agit.konect.domain.chat.dto.ChatRoomMembersResponse;
 import gg.agit.konect.domain.chat.repository.ChatRoomMemberRepository;
 import gg.agit.konect.domain.chat.repository.ChatRoomRepository;
 import gg.agit.konect.domain.club.model.Club;
@@ -39,6 +42,46 @@ public class ChatRoomMembershipService {
     private final ClubMemberRepository clubMemberRepository;
     private final UserRepository userRepository;
 
+    @Transactional(readOnly = true)
+    public ChatRoomMembersResponse getChatRoomMembers(Integer chatRoomId, Integer currentUserId) {
+        User currentUser = userRepository.findById(currentUserId)
+            .orElseThrow(() -> CustomException.of(NOT_FOUND_USER));
+
+        // 채팅방 존재 여부 먼저 확인
+        ChatRoom chatRoom = chatRoomRepository.findById(chatRoomId)
+            .orElseThrow(() -> CustomException.of(NOT_FOUND_CHAT_ROOM));
+
+        validateMembership(chatRoom, currentUser);
+
+        List<ChatRoomMember> members = chatRoomMemberRepository.findActiveMembersByChatRoomId(chatRoomId);
+
+        return new ChatRoomMembersResponse(members.stream()
+            .filter(member -> member.getUser().getDeletedAt() == null)
+            .map(this::toMemberResponse)
+            .toList());
+    }
+
+    private void validateMembership(ChatRoom chatRoom, User currentUser) {
+        // 어드민은 시스템 어드민 방의 멤버를 조회할 수 있음
+        if (currentUser.isAdmin() && isSystemAdminRoom(chatRoom.getId())) {
+            return;
+        }
+
+        if (!chatRoomMemberRepository.existsActiveByChatRoomIdAndUserId(chatRoom.getId(), currentUser.getId())) {
+            throw CustomException.of(FORBIDDEN_CHAT_ROOM_ACCESS);
+        }
+    }
+
+    private ChatRoomMemberResponse toMemberResponse(ChatRoomMember member) {
+        return new ChatRoomMemberResponse(
+            member.getUser().getId(),
+            member.getUser().getName(),
+            member.getUser().getImageUrl(),
+            member.isOwner(),
+            member.getCreatedAt()
+        );
+    }
+
     @Transactional
     public void addClubMember(ClubMember clubMember) {
         LocalDateTime baseline = Objects.requireNonNull(clubMember.getCreatedAt());