[refactor] Mapper에서 NPE 요소 제거하기 + 커스텀 예외 적용하기

backend/src/main/java/io/f1/backend/domain/game/app/GameService.java

@@ -10,6 +10,9 @@
 import io.f1.backend.domain.game.store.RoomRepository;
 import io.f1.backend.domain.quiz.app.QuizService;
 import io.f1.backend.domain.quiz.entity.Quiz;
+import io.f1.backend.global.exception.CustomException;
+import io.f1.backend.global.exception.errorcode.GameErrorCode;
+import io.f1.backend.global.exception.errorcode.RoomErrorCode;
 
 import lombok.RequiredArgsConstructor;
 
@@ -31,10 +34,10 @@ public GameStartData gameStart(Long roomId, Long quizId) {
         Room room =
                 roomRepository
                         .findRoom(roomId)
-                        .orElseThrow(() -> new IllegalArgumentException("404 존재하지 않는 방입니다."));
+                        .orElseThrow(() -> new CustomException(RoomErrorCode.ROOM_NOT_FOUND));
 
         if (!validateReadyStatus(room)) {
-            throw new IllegalArgumentException("E403004 : 레디 상태가 아닙니다.");
+            throw new CustomException(RoomErrorCode.PLAYER_NOT_READY);
         }
 
         // 방의 gameSetting에 설정된 퀴즈랑 요청 퀴즈랑 같은지 체크 후 GameSetting에서 라운드 가져오기
@@ -58,7 +61,7 @@ private Integer checkGameSetting(Room room, Long quizId) {
         GameSetting gameSetting = room.getGameSetting();
 
         if (!gameSetting.checkQuizId(quizId)) {
-            throw new IllegalArgumentException("E409002 : 게임 설정이 다릅니다. (게임을 시작할 수 없습니다.)");
+            throw new CustomException(GameErrorCode.GAME_SETTING_CONFLICT);
         }
 
         return gameSetting.getRound();

backend/src/main/java/io/f1/backend/domain/question/app/QuestionService.java

@@ -9,14 +9,14 @@
 import io.f1.backend.domain.question.entity.Question;
 import io.f1.backend.domain.question.entity.TextQuestion;
 import io.f1.backend.domain.quiz.entity.Quiz;
+import io.f1.backend.global.exception.CustomException;
+import io.f1.backend.global.exception.errorcode.QuestionErrorCode;
 
 import lombok.RequiredArgsConstructor;
 
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
-import java.util.NoSuchElementException;
-
 @Service
 @RequiredArgsConstructor
 public class QuestionService {
@@ -44,7 +44,8 @@ public void updateQuestionContent(Long questionId, String content) {
         Question question =
                 questionRepository
                         .findById(questionId)
-                        .orElseThrow(() -> new NoSuchElementException("존재하지 않는 문제입니다."));
+                        .orElseThrow(
+                                () -> new CustomException(QuestionErrorCode.QUESTION_NOT_FOUND));
 
         TextQuestion textQuestion = question.getTextQuestion();
         textQuestion.changeContent(content);
@@ -58,7 +59,8 @@ public void updateQuestionAnswer(Long questionId, String answer) {
         Question question =
                 questionRepository
                         .findById(questionId)
-                        .orElseThrow(() -> new NoSuchElementException("존재하지 않는 문제입니다."));
+                        .orElseThrow(
+                                () -> new CustomException(QuestionErrorCode.QUESTION_NOT_FOUND));
 
         question.changeAnswer(answer);
     }
@@ -69,20 +71,21 @@ public void deleteQuestion(Long questionId) {
         Question question =
                 questionRepository
                         .findById(questionId)
-                        .orElseThrow(() -> new NoSuchElementException("존재하지 않는 문제입니다."));
+                        .orElseThrow(
+                                () -> new CustomException(QuestionErrorCode.QUESTION_NOT_FOUND));
 
         questionRepository.delete(question);
     }
 
     private void validateAnswer(String answer) {
         if (answer.trim().length() < 5 || answer.trim().length() > 30) {
-            throw new IllegalArgumentException("정답은 1자 이상 30자 이하로 입력해주세요.");
+            throw new CustomException(QuestionErrorCode.INVALID_ANSWER_LENGTH);
         }
     }
 
     private void validateContent(String content) {
         if (content.trim().length() < 5 || content.trim().length() > 30) {
-            throw new IllegalArgumentException("문제는 5자 이상 30자 이하로 입력해주세요.");
+            throw new CustomException(QuestionErrorCode.INVALID_CONTENT_LENGTH);
         }
     }
 }

backend/src/main/java/io/f1/backend/domain/quiz/api/QuizController.java

@@ -6,6 +6,8 @@
 import io.f1.backend.domain.quiz.dto.QuizListPageResponse;
 import io.f1.backend.domain.quiz.dto.QuizQuestionListResponse;
 import io.f1.backend.domain.quiz.dto.QuizUpdateRequest;
+import io.f1.backend.global.exception.CustomException;
+import io.f1.backend.global.exception.errorcode.CommonErrorCode;
 
 import jakarta.validation.Valid;
 
@@ -28,8 +30,6 @@
 import org.springframework.web.bind.annotation.RestController;
 import org.springframework.web.multipart.MultipartFile;
 
-import java.io.IOException;
-
 @RestController
 @RequestMapping("/quizzes")
 @RequiredArgsConstructor
@@ -40,8 +40,7 @@ public class QuizController {
     @PostMapping(consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
     public ResponseEntity<QuizCreateResponse> saveQuiz(
             @RequestPart(required = false) MultipartFile thumbnailFile,
-            @Valid @RequestPart QuizCreateRequest request)
-            throws IOException {
+            @Valid @RequestPart QuizCreateRequest request) {
         QuizCreateResponse response = quizService.saveQuiz(thumbnailFile, request);
 
         return ResponseEntity.status(HttpStatus.CREATED).body(response);
@@ -58,8 +57,7 @@ public ResponseEntity<Void> deleteQuiz(@PathVariable Long quizId) {
     public ResponseEntity<Void> updateQuiz(
             @PathVariable Long quizId,
             @RequestPart(required = false) MultipartFile thumbnailFile,
-            @RequestPart QuizUpdateRequest request)
-            throws IOException {
+            @RequestPart QuizUpdateRequest request) {
 
         if (request.title() != null) {
             quizService.updateQuizTitle(quizId, request.title());
@@ -83,6 +81,13 @@ public ResponseEntity<QuizListPageResponse> getQuizzes(
             @RequestParam(required = false) String title,
             @RequestParam(required = false) String creator) {
 
+        if (page <= 0) {
+            throw new CustomException(CommonErrorCode.INVALID_PAGINATION);
+        }
+        if (size <= 0 || size > 100) {
+            throw new CustomException(CommonErrorCode.INVALID_PAGINATION);
+        }
+
         Pageable pageable =
                 PageRequest.of(page - 1, size, Sort.by(Sort.Direction.DESC, "createdAt"));
         QuizListPageResponse quizzes = quizService.getQuizzes(title, creator, pageable);

backend/src/main/java/io/f1/backend/domain/quiz/app/QuizService.java

@@ -17,6 +17,9 @@
 import io.f1.backend.domain.quiz.entity.Quiz;
 import io.f1.backend.domain.user.dao.UserRepository;
 import io.f1.backend.domain.user.entity.User;
+import io.f1.backend.global.exception.CustomException;
+import io.f1.backend.global.exception.errorcode.AuthErrorCode;
+import io.f1.backend.global.exception.errorcode.QuizErrorCode;
 
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
@@ -48,15 +51,15 @@ public class QuizService {
     private String defaultThumbnailPath;
 
     private final String DEFAULT = "default";
+    private static final long MAX_FILE_SIZE = 5 * 1024 * 1024; // 5MB
 
     // TODO : 시큐리티 구현 이후 삭제해도 되는 의존성 주입
     private final UserRepository userRepository;
     private final QuestionService questionService;
     private final QuizRepository quizRepository;
 
     @Transactional
-    public QuizCreateResponse saveQuiz(MultipartFile thumbnailFile, QuizCreateRequest request)
-            throws IOException {
+    public QuizCreateResponse saveQuiz(MultipartFile thumbnailFile, QuizCreateRequest request) {
         String thumbnailPath = defaultThumbnailPath;
 
         if (thumbnailFile != null && !thumbnailFile.isEmpty()) {
@@ -81,29 +84,38 @@ public QuizCreateResponse saveQuiz(MultipartFile thumbnailFile, QuizCreateReques
     private void validateImageFile(MultipartFile thumbnailFile) {
 
         if (!thumbnailFile.getContentType().startsWith("image")) {
-            // TODO : 이후 커스텀 예외로 변경
-            throw new IllegalArgumentException("이미지 파일을 업로드해주세요.");
+            throw new CustomException(QuizErrorCode.UNSUPPORTED_MEDIA_TYPE);
         }
 
         List<String> allowedExt = List.of("jpg", "jpeg", "png", "webp");
-        if (!allowedExt.contains(getExtension(thumbnailFile.getOriginalFilename()))) {
-            throw new IllegalArgumentException("지원하지 않는 확장자입니다.");
+        String ext = getExtension(thumbnailFile.getOriginalFilename());
+        if (!allowedExt.contains(ext)) {
+            throw new CustomException(QuizErrorCode.UNSUPPORTED_IMAGE_FORMAT);
+        }
+
+        if (thumbnailFile.getSize() > MAX_FILE_SIZE) {
+            throw new CustomException(QuizErrorCode.FILE_SIZE_TOO_LARGE);
         }
     }
 
-    private String convertToThumbnailPath(MultipartFile thumbnailFile) throws IOException {
+    private String convertToThumbnailPath(MultipartFile thumbnailFile) {
         String originalFilename = thumbnailFile.getOriginalFilename();
         String ext = getExtension(originalFilename);
         String savedFilename = UUID.randomUUID().toString() + "." + ext;
 
-        Path savePath = Paths.get(uploadPath, savedFilename).toAbsolutePath();
-        thumbnailFile.transferTo(savePath.toFile());
+        try {
+            Path savePath = Paths.get(uploadPath, savedFilename).toAbsolutePath();
+            thumbnailFile.transferTo(savePath.toFile());
+        } catch (IOException e) {
+            log.error("썸네일 업로드 중 IOException 발생", e);
+            throw new CustomException(QuizErrorCode.THUMBNAIL_SAVE_FAILED);
+        }
 
         return "/images/thumbnail/" + savedFilename;
     }
 
     private String getExtension(String filename) {
-        return filename.substring(filename.lastIndexOf(".") + 1);
+        return filename.substring(filename.lastIndexOf(".") + 1).toLowerCase();
     }
 
     @Transactional
@@ -112,11 +124,11 @@ public void deleteQuiz(Long quizId) {
         Quiz quiz =
                 quizRepository
                         .findById(quizId)
-                        .orElseThrow(() -> new NoSuchElementException("존재하지 않는 퀴즈입니다."));
+                        .orElseThrow(() -> new CustomException(QuizErrorCode.QUIZ_NOT_FOUND));
 
         // TODO : util 메서드에서 사용자 ID 꺼내쓰는 식으로 수정하기
         if (1L != quiz.getCreator().getId()) {
-            throw new RuntimeException("권한이 없습니다.");
+            throw new CustomException(AuthErrorCode.FORBIDDEN);
         }
 
         deleteThumbnailFile(quiz.getThumbnailUrl());
@@ -128,7 +140,7 @@ public void updateQuizTitle(Long quizId, String title) {
         Quiz quiz =
                 quizRepository
                         .findById(quizId)
-                        .orElseThrow(() -> new NoSuchElementException("존재하지 않는 퀴즈입니다."));
+                        .orElseThrow(() -> new CustomException(QuizErrorCode.QUIZ_NOT_FOUND));
 
         validateTitle(title);
         quiz.changeTitle(title);
@@ -140,19 +152,19 @@ public void updateQuizDesc(Long quizId, String description) {
         Quiz quiz =
                 quizRepository
                         .findById(quizId)
-                        .orElseThrow(() -> new NoSuchElementException("존재하지 않는 퀴즈입니다."));
+                        .orElseThrow(() -> new CustomException(QuizErrorCode.QUIZ_NOT_FOUND));
 
         validateDesc(description);
         quiz.changeDescription(description);
     }
 
     @Transactional
-    public void updateThumbnail(Long quizId, MultipartFile thumbnailFile) throws IOException {
+    public void updateThumbnail(Long quizId, MultipartFile thumbnailFile) {
 
         Quiz quiz =
                 quizRepository
                         .findById(quizId)
-                        .orElseThrow(() -> new NoSuchElementException("존재하지 않는 퀴즈입니다."));
+                        .orElseThrow(() -> new CustomException(QuizErrorCode.QUIZ_NOT_FOUND));
 
         validateImageFile(thumbnailFile);
         String newThumbnailPath = convertToThumbnailPath(thumbnailFile);
@@ -163,13 +175,13 @@ public void updateThumbnail(Long quizId, MultipartFile thumbnailFile) throws IOE
 
     private void validateDesc(String desc) {
         if (desc.trim().length() < 10 || desc.trim().length() > 50) {
-            throw new IllegalArgumentException("설명은 10자 이상 50자 이하로 입력해주세요.");
+            throw new CustomException(QuizErrorCode.INVALID_DESC_LENGTH);
         }
     }
 
     private void validateTitle(String title) {
         if (title.trim().length() < 2 || title.trim().length() > 30) {
-            throw new IllegalArgumentException("제목은 2자 이상 30자 이하로 입력해주세요.");
+            throw new CustomException(QuizErrorCode.INVALID_TITLE_LENGTH);
         }
     }
 
@@ -192,7 +204,7 @@ private void deleteThumbnailFile(String oldFilename) {
             }
         } catch (IOException e) {
             log.error("기존 썸네일 삭제 중 오류 : {}", filePath);
-            throw new RuntimeException(e);
+            throw new CustomException(QuizErrorCode.THUMBNAIL_DELETE_FAILED);
         }
     }
 
@@ -202,9 +214,9 @@ public QuizListPageResponse getQuizzes(String title, String creator, Pageable pa
         Page<Quiz> quizzes;
 
         // 검색어가 있을 때
-        if (StringUtils.isBlank(title)) {
+        if (!StringUtils.isBlank(title)) {
             quizzes = quizRepository.findQuizzesByTitleContaining(title, pageable);
-        } else if (StringUtils.isBlank(creator)) {
+        } else if (!StringUtils.isBlank(creator)) {
             quizzes = quizRepository.findQuizzesByCreator_NicknameContaining(creator, pageable);
         } else { // 검색어가 없을 때 혹은 빈 문자열일 때
             quizzes = quizRepository.findAll(pageable);
@@ -220,7 +232,7 @@ public Quiz getQuizWithQuestionsById(Long quizId) {
         Quiz quiz =
                 quizRepository
                         .findQuizWithQuestionsById(quizId)
-                        .orElseThrow(() -> new RuntimeException("E404002: 존재하지 않는 퀴즈입니다."));
+                        .orElseThrow(() -> new CustomException(QuizErrorCode.QUIZ_NOT_FOUND));
         return quiz;
     }
 
@@ -234,7 +246,7 @@ public QuizQuestionListResponse getQuizWithQuestions(Long quizId) {
         Quiz quiz =
                 quizRepository
                         .findById(quizId)
-                        .orElseThrow(() -> new NoSuchElementException("존재하지 않는 퀴즈입니다."));
+                        .orElseThrow(() -> new CustomException(QuizErrorCode.QUIZ_NOT_FOUND));
 
         return quizToQuizQuestionListResponse(quiz);
     }

backend/src/main/java/io/f1/backend/domain/quiz/entity/Quiz.java

@@ -50,7 +50,7 @@ public class Quiz extends BaseEntity {
     private String thumbnailUrl;
 
     @ManyToOne
-    @JoinColumn(name = "creator_id")
+    @JoinColumn(name = "creator_id", nullable = true)
     private User creator;
 
     public Quiz(
@@ -81,4 +81,20 @@ public void changeDescription(String description) {
     public void changeThumbnailUrl(String thumbnailUrl) {
         this.thumbnailUrl = thumbnailUrl;
     }
+
+    public Long getUserIdIfExists() {
+        if (this.creator == null) {
+            return null;
+        }
+
+        return this.creator.getId();
+    }
+
+    public String getUserNicknameIfExists() {
+        if (this.creator == null) {
+            return "탈퇴한 사용자";
+        }
+
+        return this.creator.getNickname();
+    }
 }

backend/src/main/java/io/f1/backend/domain/quiz/mapper/QuizMapper.java

@@ -39,15 +39,15 @@ public static QuizCreateResponse quizToQuizCreateResponse(Quiz quiz) {
                 quiz.getQuizType(),
                 quiz.getDescription(),
                 quiz.getThumbnailUrl(),
-                quiz.getCreator().getId());
+                quiz.getUserIdIfExists());
     }
 
     public static QuizListResponse quizToQuizListResponse(Quiz quiz) {
         return new QuizListResponse(
                 quiz.getId(),
                 quiz.getTitle(),
                 quiz.getDescription(),
-                quiz.getCreator().getNickname(),
+                quiz.getUserNicknameIfExists(),
                 quiz.getQuestions().size(),
                 quiz.getThumbnailUrl());
     }
@@ -79,7 +79,7 @@ public static QuizQuestionListResponse quizToQuizQuestionListResponse(Quiz quiz)
         return new QuizQuestionListResponse(
                 quiz.getTitle(),
                 quiz.getQuizType(),
-                quiz.getCreator().getId(),
+                quiz.getUserIdIfExists(),
                 quiz.getDescription(),
                 quiz.getThumbnailUrl(),
                 quiz.getQuestions().size(),

backend/src/main/java/io/f1/backend/global/exception/errorcode/GameErrorCode.java

@@ -0,0 +1,18 @@
+package io.f1.backend.global.exception.errorcode;
+
+import lombok.Getter;
+import lombok.RequiredArgsConstructor;
+
+import org.springframework.http.HttpStatus;
+
+@Getter
+@RequiredArgsConstructor
+public enum GameErrorCode implements ErrorCode {
+    GAME_SETTING_CONFLICT("E409002", HttpStatus.CONFLICT, "게임 설정이 맞지 않습니다.");
+
+    private final String code;
+
+    private final HttpStatus httpStatus;
+
+    private final String message;
+}