#74 ✨ feat: item이 저장된 폴더 목록 반환 api 추가

Author: ramen0519

src/main/java/com/finsight/finsight/domain/storage/domain/service/FolderService.java

@@ -9,6 +9,7 @@
 import com.finsight.finsight.domain.storage.exception.StorageException;
 import com.finsight.finsight.domain.storage.exception.code.StorageErrorCode;
 import com.finsight.finsight.domain.storage.persistence.entity.FolderEntity;
+import com.finsight.finsight.domain.storage.persistence.entity.FolderItemEntity;
 import com.finsight.finsight.domain.storage.persistence.entity.FolderType;
 import com.finsight.finsight.domain.storage.persistence.repository.FolderItemRepository;
 import com.finsight.finsight.domain.storage.persistence.repository.FolderRepository;
@@ -140,4 +141,27 @@ public List<FolderResponse> updateFolderOrder(Long userId, UpdateFolderOrderRequ
 
         return getFolders(userId, folderType);
     }
+
+    /**
+     * 특정 아이템(뉴스/용어)이 저장된 폴더 목록 조회
+     */
+    public List<FolderResponse> getItemFolders(Long userId, String type, Long itemId) {
+        FolderType folderType;
+        try {
+            folderType = FolderType.valueOf(type.toUpperCase());
+        } catch (IllegalArgumentException e) {
+            throw new StorageException(StorageErrorCode.FOLDER_TYPE_MISMATCH);
+        }
+
+        List<FolderItemEntity> items = folderItemRepository.findByUserIdAndItemTypeAndItemId(
+                userId, folderType, itemId);
+
+        return items.stream()
+                .map(item -> {
+                    FolderEntity folder = item.getFolder();
+                    long itemCount = folderItemRepository.countByFolderFolderId(folder.getFolderId());
+                    return FolderResponse.from(folder, itemCount);
+                })
+                .toList();
+    }
 }

src/main/java/com/finsight/finsight/domain/storage/presentation/FolderController.java

@@ -77,4 +77,15 @@ public ResponseEntity<DataResponse<List<FolderResponse>>> updateFolderOrder(
         List<FolderResponse> response = folderService.updateFolderOrder(userDetails.getUserId(), request);
         return ResponseEntity.ok(DataResponse.from(response));
     }
+
+    @GetMapping("/items/{itemId}")
+    @Operation(summary = "아이템이 저장된 폴더 조회", description = "특정 뉴스/용어가 저장된 폴더 목록을 반환합니다.")
+    public ResponseEntity<DataResponse<List<FolderResponse>>> getItemFolders(
+            @AuthenticationPrincipal CustomUserDetails userDetails,
+            @PathVariable Long itemId,
+            @RequestParam String type
+    ) {
+        List<FolderResponse> response = folderService.getItemFolders(userDetails.getUserId(), type, itemId);
+        return ResponseEntity.ok(DataResponse.from(response));
+    }
 }