perf: post 커서 기반 페이징

src/main/java/inu/codin/codin/domain/post/controller/PostController.java

@@ -6,15 +6,18 @@
 import inu.codin.codin.domain.post.dto.request.PostContentUpdateRequestDTO;
 import inu.codin.codin.domain.post.dto.request.PostCreateRequestDTO;
 import inu.codin.codin.domain.post.dto.request.PostStatusUpdateRequestDTO;
+import inu.codin.codin.domain.post.dto.response.CursorPageResponse;
 import inu.codin.codin.domain.post.dto.response.PostDetailResponseDTO;
 import inu.codin.codin.domain.post.dto.response.PostPageResponse;
 import inu.codin.codin.domain.post.entity.PostCategory;
+import inu.codin.codin.domain.post.service.PostCursorService;
 import inu.codin.codin.domain.post.service.PostService;
 import io.swagger.v3.oas.annotations.Operation;
 import io.swagger.v3.oas.annotations.tags.Tag;
 import jakarta.validation.Valid;
 import jakarta.validation.constraints.NotNull;
 import jakarta.validation.constraints.Size;
+import lombok.RequiredArgsConstructor;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
 import org.springframework.http.ResponseEntity;
@@ -28,13 +31,11 @@
 @RequestMapping("/posts")
 @Validated
 @Tag(name = "POST API", description = "게시글 API")
+@RequiredArgsConstructor
 public class PostController {
 
     private final PostService postService;
-
-    public PostController(PostService postService) {
-        this.postService = postService;
-    }
+    private final PostCursorService postCursorService;
 
     @Operation(
             summary = "게시물 작성",
@@ -152,4 +153,15 @@ public ResponseEntity<SingleResponse<?>> getBestPosts(@RequestParam("pageNumber"
         return ResponseEntity.ok()
                 .body(new SingleResponse<>(200, "Top3로 선정된 게시글들 모두 반환 완료", postService.getBestPosts(pageNumber)));
     }
+
+    @Operation(summary = "카테고리별 삭제되지 않은 게시물 조회 - 커서(ObjectId) 기반")
+    @GetMapping("/category/cursor")
+    public ResponseEntity<SingleResponse<CursorPageResponse<PostDetailResponseDTO>>> getAllPostsCursor(
+            @RequestParam PostCategory postCategory,
+            @RequestParam(required = false) String cursor,
+            @RequestParam(defaultValue = "20") int limit
+    ) {
+        return ResponseEntity.ok(new SingleResponse<>(200, "커서 기반 카테고리별 게시물 조회 성공",
+                postCursorService.getAllPostsByCursorIdOnly(postCategory, cursor, Math.min(limit, 100))));
+    }
 }

src/main/java/inu/codin/codin/domain/post/dto/response/CursorPageResponse.java

@@ -0,0 +1,14 @@
+package inu.codin.codin.domain.post.dto.response;
+
+import lombok.Builder;
+import lombok.Getter;
+
+import java.util.List;
+
+@Getter
+@Builder
+public class CursorPageResponse<T> {
+    private final List<T> items;
+    private final String nextCursor; // 다음 페이지 커서 값
+    private final boolean hasNext;
+}

src/main/java/inu/codin/codin/domain/post/repository/PostReadRepository.java

@@ -0,0 +1,54 @@
+package inu.codin.codin.domain.post.repository;
+
+import inu.codin.codin.domain.post.entity.PostEntity;
+import lombok.RequiredArgsConstructor;
+import org.bson.types.ObjectId;
+import org.springframework.data.domain.Sort;
+import org.springframework.data.mongodb.core.MongoTemplate;
+import org.springframework.data.mongodb.core.query.Criteria;
+import org.springframework.data.mongodb.core.query.Query;
+import org.springframework.stereotype.Repository;
+
+import java.util.List;
+import java.util.regex.Pattern;
+
+@Repository
+@RequiredArgsConstructor
+public class PostReadRepository {
+
+    private final MongoTemplate mongoTemplate;
+
+    /**
+     * 커서 기반 MongoDB posts 컬렉션 조회 기능
+     * @param postCategory 게시물 카테고리 PostCategory.
+     * @param blockedUsers 차단된 유저 id 리스트
+     * @param cursorId 커서 id - 마지막으로 본 post
+     * @param limit 페이지 크기
+     * @return List<PostEntity>
+     */
+    public List<PostEntity> findByCategoryWithIdCursor(String postCategory, List<ObjectId> blockedUsers, ObjectId cursorId, int limit) {
+        Criteria base = new Criteria().andOperator(
+                new Criteria().orOperator(
+                        Criteria.where("deleted_at").is(null),
+                        Criteria.where("deleted_at").exists(false)
+                ),
+                Criteria.where("postStatus").is("ACTIVE"),
+                Criteria.where("postCategory").is(postCategory)
+        );
+
+        // 차단 유저가 없을 때
+        if (blockedUsers != null && !blockedUsers.isEmpty()) {
+            base = new Criteria().andOperator(base, Criteria.where("userId").nin(blockedUsers));
+        }
+        // 첫번째 페이지 조회
+        if (cursorId != null) {
+            base = new Criteria().andOperator(base, Criteria.where("_id").lt(cursorId));
+        }
+
+        Query query = new Query(base)
+                .with(Sort.by(Sort.Direction.DESC, "_id"))
+                .limit(limit + 1);
+
+        return mongoTemplate.find(query, PostEntity.class, "posts");
+    }
+}

src/main/java/inu/codin/codin/domain/post/service/PostCursorService.java

@@ -0,0 +1,62 @@
+package inu.codin.codin.domain.post.service;
+
+import inu.codin.codin.common.util.ObjectIdUtil;
+import inu.codin.codin.domain.block.service.BlockService;
+import inu.codin.codin.domain.post.dto.response.CursorPageResponse;
+import inu.codin.codin.domain.post.dto.response.PostDetailResponseDTO;
+import inu.codin.codin.domain.post.entity.PostCategory;
+import inu.codin.codin.domain.post.entity.PostEntity;
+import inu.codin.codin.domain.post.repository.PostReadRepository;
+import lombok.RequiredArgsConstructor;
+import org.bson.types.ObjectId;
+import org.springframework.stereotype.Service;
+
+import java.util.List;
+
+@Service
+@RequiredArgsConstructor
+public class PostCursorService {
+
+    private final PostReadRepository postReadRepository;
+    private final BlockService blockService;
+    private final PostService postService;
+
+    /**
+     * 커서 기반 조회 서비스 로직
+     * @param category 게시글 카테고리
+     * @param cursor 마지막 커서 id
+     * @param limit 조회 개수
+     * @return CursorPageResponse<PostDetailResponseDTO> 반환
+     */
+    public CursorPageResponse<PostDetailResponseDTO> getAllPostsByCursorIdOnly(PostCategory category, String cursor, int limit) {
+        List<ObjectId> blockedUsers = blockService.getBlockedUsers();
+
+        // objectId가 24자리 16진수 검증
+        ObjectId lastId = null;
+        if (cursor != null && cursor.matches("^[a-fA-F0-9]{24}$")) {
+            lastId = ObjectIdUtil.toObjectId(cursor);
+        } else if (cursor != null && !cursor.isBlank()) {
+            throw new IllegalArgumentException("cursor는 24자리 hex(ObjectId)여야 합니다.");
+        }
+
+        List<PostEntity> batch = postReadRepository.findByCategoryWithIdCursor(category.name(), blockedUsers, lastId, limit);
+
+        // 다음 페이지 계산
+        boolean hasNext = batch.size() > limit;
+        if (hasNext) batch = batch.subList(0, limit);
+
+        // 다음 커서 id 생성
+        String nextCursor = null;
+        if (hasNext && !batch.isEmpty()) {
+            PostEntity tail = batch.get(batch.size() - 1);
+            nextCursor = ObjectIdUtil.toString(tail.get_id());
+        }
+
+        List<PostDetailResponseDTO> items = postService.getPostListResponseDtos(batch);
+        return CursorPageResponse.<PostDetailResponseDTO>builder()
+                .items(items)
+                .hasNext(hasNext)
+                .nextCursor(nextCursor)
+                .build();
+    }
+}