✨ Feat/#314 이전 내용 불러오기 기능 구현

backend/src/main/java/org/example/backend/domain/question/controller/QuestionController.java

@@ -38,4 +38,11 @@ public ApiResponse<?> getQuestions(@PathVariable("lectureId") UUID lectureId) {
             return ApiResponse.onSuccess(result);
         }
     }
+
+    // 이전 내용 불러오기
+    @GetMapping("/chatting/before/{lectureId}")
+    public ApiResponse<List<QuestionResponseDTO.beforeChatting>> getBeforeChatting(@PathVariable("lectureId") UUID lectureId) {
+        List<QuestionResponseDTO.beforeChatting> result = questionService.getBeforeChatting(lectureId);
+        return ApiResponse.onSuccess(result);
+    }
 }

backend/src/main/java/org/example/backend/domain/question/dto/response/QuestionResponseDTO.java

@@ -4,6 +4,7 @@
 import lombok.Builder;
 import lombok.Getter;
 import lombok.NoArgsConstructor;
+import org.example.backend.domain.user.entity.Role;
 
 import java.time.LocalDateTime;
 import java.util.UUID;
@@ -33,4 +34,14 @@ public static class student {
         private String content;
     }
 
+    @Builder
+    @Getter
+    @NoArgsConstructor
+    @AllArgsConstructor
+    public static class beforeChatting {
+        private String content;
+        private LocalDateTime timestamp;
+        private Role role;
+    }
+
 }

backend/src/main/java/org/example/backend/domain/question/exception/QuestionErrorCode.java

@@ -10,7 +10,8 @@
 @AllArgsConstructor
 public enum QuestionErrorCode implements BaseErrorCode {
     _FORBIDDEN_LECTURE_ACCESS(HttpStatus.FORBIDDEN,"QUESTION403_1","해당 강의를 수강중인 학생만 조회가능합니다."),
-    _CHAT_MESSAGE_SEND_FAIL(HttpStatus.INTERNAL_SERVER_ERROR, "QUESTION500_1", "채팅 메시지 전송에 실패했습니다.");
+    _CHAT_MESSAGE_SEND_FAIL(HttpStatus.INTERNAL_SERVER_ERROR, "QUESTION500_1", "채팅 메시지 전송에 실패했습니다."),
+    _INVALID_JSON_FORMAT(HttpStatus.BAD_REQUEST,"QUESTION400_1","저장된 채팅 데이터를 읽는 데 실패했습니다.");
 
     private final HttpStatus httpStatus;
     private final String code;

backend/src/main/java/org/example/backend/domain/question/service/QuestionService.java

@@ -11,4 +11,6 @@ public interface QuestionService {
     List<QuestionResponseDTO.teacher> getTeacherQuestions(UUID lectureId, User user);
     //학생용 질문 조회
     List<QuestionResponseDTO.student> getStudentQuestions(UUID lectureId, User user);
+    // 이전 채팅 내용 불러오개
+    List<QuestionResponseDTO.beforeChatting> getBeforeChatting(UUID lectureId);
 }

backend/src/main/java/org/example/backend/domain/question/service/QuestionServiceImpl.java

@@ -1,5 +1,7 @@
 package org.example.backend.domain.question.service;
 
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
 import lombok.RequiredArgsConstructor;
 import org.example.backend.domain.question.converter.QuestionConverter;
 import org.example.backend.domain.question.dto.response.QuestionResponseDTO;
@@ -8,8 +10,11 @@
 import org.example.backend.domain.question.repository.QuestionRepository;
 import org.example.backend.domain.studentClass.repository.StudentClassRepository;
 import org.example.backend.domain.user.entity.User;
+import org.springframework.data.redis.core.RedisTemplate;
 import org.springframework.stereotype.Service;
 
+import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.UUID;
 
@@ -20,6 +25,8 @@ public class QuestionServiceImpl implements QuestionService {
     private final QuestionRepository questionRepository;
     private final StudentClassRepository studentClassRepository;
     private final QuestionConverter questionConverter;
+    private final RedisTemplate<String,String> redisTemplate;
+    private final ObjectMapper objectMapper;
 
     @Override
     public List<QuestionResponseDTO.teacher> getTeacherQuestions(UUID lectureId, User user ) {
@@ -41,4 +48,34 @@ public List<QuestionResponseDTO.student> getStudentQuestions(UUID lectureId, Use
                 .map(questionConverter::toStudentQuestions)
                 .toList();
     }
+
+    // 이전 내용 불러오기
+    @Override
+    public List<QuestionResponseDTO.beforeChatting> getBeforeChatting(UUID lectureId) {
+        String redisKey = "chat:lecture:" + lectureId;
+
+        List<String> rawMessages = redisTemplate.opsForList().range(redisKey, 0, -1);
+
+        // 이전 내용이 없다면 빈배열 반환
+        if(rawMessages == null || rawMessages.isEmpty()){
+            return Collections.emptyList();
+        }
+
+        // 반환리스트
+        List<QuestionResponseDTO.beforeChatting> chatList = new ArrayList<>();
+
+        // 최신 메시지가 먼저 저장됨 -> 역순으로 순회
+        for(int i=rawMessages.size()-1;i>=0;i--){
+            try{
+                // JSON 문자열 -> DTO 변환
+                QuestionResponseDTO.beforeChatting dto = objectMapper.readValue(rawMessages.get(i), QuestionResponseDTO.beforeChatting.class);
+                chatList.add(dto);
+            }
+            catch (JsonProcessingException e){
+                // 파싱 실패
+                throw new QuestionException(QuestionErrorCode._INVALID_JSON_FORMAT);
+            }
+        }
+        return chatList;
+    }
 }