Develop

src/main/java/com/jiwon/mylog/domain/post/controller/PostController.java

@@ -1,5 +1,6 @@
 package com.jiwon.mylog.domain.post.controller;
 
+import com.jiwon.mylog.domain.post.dto.response.PostNavigationResponse;
 import com.jiwon.mylog.domain.post.service.PostService;
 import com.jiwon.mylog.domain.post.service.PostViewService;
 import com.jiwon.mylog.global.security.auth.annotation.AllUser;
@@ -122,6 +123,24 @@ public ResponseEntity<PageResponse> getPosts(
         return new ResponseEntity<>(response, HttpStatus.OK);
     }
 
+    @GetMapping("/posts/{postId}/navigation")
+    @Operation(
+            summary = "현재 게시글의 정보(카테고리 ID, 카테고리 내에서의 현재 page, offset)를 획득한다."
+    )
+    public ResponseEntity<PostNavigationResponse> getPostNavigation(@PathVariable("postId") Long postId) {
+        PostNavigationResponse response = postService.getPostNavigation(postId);
+        return ResponseEntity.ok(response);
+    }
+
+    @GetMapping("/categories/{categoryId}/posts")
+    public ResponseEntity<PageResponse> getCategorizedPosts(
+            @PathVariable("categoryId") Long categoryId,
+            @RequestParam Long userId,
+            @PageableDefault(size = 5, sort = "createdAt", direction = Direction.DESC) Pageable pageable) {
+        PageResponse response = postService.getCategorizedPosts(categoryId, userId, pageable);
+        return ResponseEntity.ok(response);
+    }
+
     @GetMapping("/users/{userId}/categories/{categoryId}/posts")
     @Operation(
             summary = "특정 유저의 카테고리별 게시글 조회 (태그 필터링 및 키워드 검색 포함)",

src/main/java/com/jiwon/mylog/domain/post/dto/response/PostDetailResponse.java

@@ -36,6 +36,8 @@ public class PostDetailResponse {
     private CategoryResponse category;
     private List<TagResponse> tags;
     private List<CommentResponse> comments;
+    private RelatedPostResponse previousPost;
+    private RelatedPostResponse nextPost;
 
     public PostDetailResponse(Long postId, String title, String content, String contentPreview, int views, PostStatus postStatus, Visibility visibility, LocalDateTime createdAt, boolean pinned, PostType type, UserResponse user, CategoryResponse category) {
         this.postId = postId;
@@ -75,6 +77,11 @@ public static PostDetailResponse fromPost(Post post) {
                 .build();
     }
 
+    public void setRelatedPosts(RelatedPostResponse previous, RelatedPostResponse next) {
+        this.previousPost = previous;
+        this.nextPost = next;
+    }
+
     public void setViews(int views) {
         this.views = views;
     }

src/main/java/com/jiwon/mylog/domain/post/dto/response/PostNavigationResponse.java

@@ -0,0 +1,17 @@
+package com.jiwon.mylog.domain.post.dto.response;
+
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Getter;
+
+@Builder
+@AllArgsConstructor
+@Getter
+public class PostNavigationResponse {
+    private final Long postId;
+    private final Long userId;
+    private final Long categoryId;
+    private final Long currentOffset;
+    private final Long currentPage;
+    private final Long totalPosts;
+}

src/main/java/com/jiwon/mylog/domain/post/dto/response/RelatedPostResponse.java

@@ -0,0 +1,20 @@
+package com.jiwon.mylog.domain.post.dto.response;
+
+import lombok.Builder;
+import lombok.Getter;
+
+import java.time.LocalDateTime;
+
+@Getter
+@Builder
+public class RelatedPostResponse {
+    private final Long postId;
+    private final String title;
+    private final LocalDateTime createdAt;
+
+    public RelatedPostResponse(Long postId, String title, LocalDateTime createdAt) {
+        this.postId = postId;
+        this.title = title;
+        this.createdAt = createdAt;
+    }
+}

src/main/java/com/jiwon/mylog/domain/post/repository/PostRepositoryCustom.java

@@ -1,8 +1,9 @@
 package com.jiwon.mylog.domain.post.repository;
 
 import com.jiwon.mylog.domain.post.dto.response.PostDetailResponse;
+import com.jiwon.mylog.domain.post.dto.response.PostNavigationResponse;
 import com.jiwon.mylog.domain.post.dto.response.PostSummaryResponse;
-import com.jiwon.mylog.domain.post.entity.Post;
+import com.jiwon.mylog.domain.post.dto.response.RelatedPostResponse;
 import com.jiwon.mylog.domain.user.dto.response.UserActivityResponse;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
@@ -19,4 +20,8 @@ public interface PostRepositoryCustom {
     Optional<PostDetailResponse> findPostDetail(Long postId);
 
     List<UserActivityResponse> findUserActivities(Long userId, LocalDate start, LocalDate end);
+
+    PostNavigationResponse findPostNavigation(Long postId);
+
+    Page<RelatedPostResponse> findCategorizedPosts(Long categoryId, Long userId, Pageable pageable);
 }

src/main/java/com/jiwon/mylog/domain/post/repository/PostRepositoryImpl.java

@@ -7,7 +7,9 @@
 import com.jiwon.mylog.domain.image.entity.QProfileImage;
 import com.jiwon.mylog.domain.like.QLike;
 import com.jiwon.mylog.domain.post.dto.response.PostDetailResponse;
+import com.jiwon.mylog.domain.post.dto.response.PostNavigationResponse;
 import com.jiwon.mylog.domain.post.dto.response.PostSummaryResponse;
+import com.jiwon.mylog.domain.post.dto.response.RelatedPostResponse;
 import com.jiwon.mylog.domain.post.entity.QPost;
 import com.jiwon.mylog.domain.tag.dto.response.TagResponse;
 import com.jiwon.mylog.domain.tag.entity.QPostTag;
@@ -17,6 +19,7 @@
 import com.jiwon.mylog.domain.user.dto.response.UserSummaryResponse;
 import com.jiwon.mylog.domain.user.entity.QUser;
 import com.querydsl.core.BooleanBuilder;
+import com.querydsl.core.Tuple;
 import com.querydsl.core.types.Projections;
 import com.querydsl.core.types.dsl.BooleanExpression;
 import com.querydsl.core.types.dsl.DateTemplate;
@@ -27,6 +30,7 @@
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.PageImpl;
+import org.springframework.data.domain.PageRequest;
 import org.springframework.data.domain.Pageable;
 import org.springframework.stereotype.Repository;
 
@@ -47,6 +51,9 @@ public class PostRepositoryImpl implements PostRepositoryCustom {
 
     private final JPAQueryFactory jpaQueryFactory;
     private static final QPost POST = QPost.post;
+    private static final QPost PREV_POST = new QPost("prev");
+    private static final QPost NEXT_POST = new QPost("next");
+    private static final QPost SUB_POST = new QPost("sub");
     private static final QUser USER = QUser.user;
     private static final QProfileImage PROFILE_IMAGE = QProfileImage.profileImage;
     private static final QCategory CATEGORY = QCategory.category;
@@ -153,7 +160,21 @@ public Optional<PostDetailResponse> findPostDetail(Long postId) {
             return Optional.empty();
         }
 
-        List<TagResponse> tags = jpaQueryFactory
+        List<TagResponse> tags = getTagsByPostId(postId);
+        List<CommentResponse> comments = getCommentsByPostId(postId);
+
+        Tuple postData = getPostData(postId);
+        RelatedPostResponse previousPost = findPreviousPost(postData);
+        RelatedPostResponse nextPost = findNextPost(postData);
+
+        postDetailResponse.setTagsAndComments(tags, comments);
+        postDetailResponse.setRelatedPosts(previousPost, nextPost);
+
+        return Optional.of(postDetailResponse);
+    }
+
+    private List<TagResponse> getTagsByPostId(Long postId) {
+        return jpaQueryFactory
                 .select(Projections.constructor(TagResponse.class,
                         TAG.id,
                         TAG.name
@@ -163,8 +184,10 @@ public Optional<PostDetailResponse> findPostDetail(Long postId) {
                 .where(POST_TAG.post.id.eq(postId))
                 .orderBy(POST_TAG.id.asc())
                 .fetch();
+    }
 
-        List<CommentResponse> comments = jpaQueryFactory
+    private List<CommentResponse> getCommentsByPostId(Long postId) {
+        return jpaQueryFactory
                 .select(Projections.constructor(CommentResponse.class,
                                 COMMENT.id,
                                 COMMENT.parent.id,
@@ -190,9 +213,138 @@ public Optional<PostDetailResponse> findPostDetail(Long postId) {
                 .where(COMMENT.post.id.eq(postId))
                 .orderBy(COMMENT.createdAt.desc())
                 .fetch();
+    }
 
-        postDetailResponse.setTagsAndComments(tags, comments);
-        return Optional.of(postDetailResponse);
+    @Override
+    public PostNavigationResponse findPostNavigation(Long postId) {
+
+        Tuple postData = getPostData(postId);
+        if (postData == null) {
+            return null;
+        }
+
+        Long defaultPageSize = 5L;
+
+        Long userId = postData.get(0, Long.class);
+        Long categoryId = postData.get(1, Long.class);
+        LocalDateTime createdAt = postData.get(2, LocalDateTime.class);
+
+        BooleanBuilder conditions = createCategorizedDefaultConditions(userId, categoryId);
+        Long total = createCountQuery(conditions);
+        Long offset = createCountQuery(conditions.and(POST.createdAt.gt(createdAt)));
+
+        long currentPage = offset / defaultPageSize;
+        long currentPageOffset = offset - (offset % defaultPageSize);
+
+        return PostNavigationResponse.builder()
+                .postId(postId)
+                .userId(userId)
+                .categoryId(categoryId)
+                .currentOffset(currentPageOffset)
+                .currentPage(currentPage)
+                .totalPosts(total)
+                .build();
+    }
+
+    @Override
+    public Page<RelatedPostResponse> findCategorizedPosts(Long categoryId, Long userId, Pageable pageable) {
+        BooleanBuilder conditions = createCategorizedDefaultConditions(userId, categoryId);
+        List<RelatedPostResponse> categorizedPosts =
+                createdCategorizedPostsQuery(conditions, pageable);
+        Long total = createCountQuery(conditions);
+        return new PageImpl<>(categorizedPosts, pageable, total);
+    }
+
+    private BooleanBuilder createCategorizedDefaultConditions(Long userId, Long categoryId) {
+        BooleanBuilder conditions = new BooleanBuilder()
+                .and(POST.user.id.eq(userId))
+                .and(POST.deletedAt.isNull());
+
+        if (categoryId != null && categoryId > 0L) {
+            conditions.and(POST.category.id.eq(categoryId));
+        } else {
+            conditions.and(POST.category.isNull());
+        }
+
+        return conditions;
+    }
+
+    private List<RelatedPostResponse> createdCategorizedPostsQuery(BooleanBuilder conditions, Pageable pageable) {
+        return jpaQueryFactory
+                .select(Projections.constructor(RelatedPostResponse.class,
+                                POST.id, POST.title, POST.createdAt
+                        )
+                )
+                .from(POST)
+                .where(conditions)
+                .orderBy(POST.createdAt.desc())
+                .offset(pageable.getOffset())
+                .limit(pageable.getPageSize())
+                .fetch();
+    }
+
+    private RelatedPostResponse findPreviousPost(Tuple currentPost) {
+
+        if (currentPost == null) {
+            return null;
+        }
+
+        Long userId = currentPost.get(0, Long.class);
+        Long categoryId = currentPost.get(1, Long.class);
+        LocalDateTime createdAt = currentPost.get(2, LocalDateTime.class);
+
+        BooleanBuilder conditions =
+                createCategorizedDefaultConditions(userId, categoryId)
+                .and(POST.createdAt.lt(createdAt));
+
+        return jpaQueryFactory
+                .select(Projections.constructor(RelatedPostResponse.class,
+                                POST.id, POST.title, POST.createdAt
+                        )
+                )
+                .from(POST)
+                .where(conditions)
+                .orderBy(POST.createdAt.desc())
+                .limit(1)
+                .fetchOne();
+    }
+
+    private RelatedPostResponse findNextPost(Tuple currentPost) {
+
+        if (currentPost == null) {
+            return null;
+        }
+
+        Long userId = currentPost.get(0, Long.class);
+        Long categoryId = currentPost.get(1, Long.class);
+        LocalDateTime createdAt = currentPost.get(2, LocalDateTime.class);
+
+        BooleanBuilder conditions =
+                createCategorizedDefaultConditions(userId, categoryId)
+                .and(POST.createdAt.gt(createdAt));
+
+        return jpaQueryFactory
+                .select(Projections.constructor(RelatedPostResponse.class,
+                                POST.id, POST.title, POST.createdAt
+                        )
+                )
+                .from(POST)
+                .where(conditions)
+                .orderBy(POST.createdAt.asc())
+                .limit(1)
+                .fetchOne();
+    }
+
+    private Tuple getPostData(Long postId) {
+        Tuple currentPost = jpaQueryFactory
+                .select(POST.user.id,
+                        POST.category.id.coalesce(-1L),
+                        POST.createdAt
+                )
+                .from(POST)
+                .where(POST.id.eq(postId))
+                .fetchOne();
+        return currentPost;
     }
 
     @Override

src/main/java/com/jiwon/mylog/domain/post/service/PostService.java

@@ -7,6 +7,8 @@
 import com.jiwon.mylog.domain.post.dto.response.MainPostResponse;
 import com.jiwon.mylog.domain.post.dto.response.NoticePostResponse;
 import com.jiwon.mylog.domain.post.dto.response.PostDetailResponse;
+import com.jiwon.mylog.domain.post.dto.response.PostNavigationResponse;
+import com.jiwon.mylog.domain.post.dto.response.RelatedPostResponse;
 import com.jiwon.mylog.global.common.entity.PageResponse;
 import com.jiwon.mylog.domain.post.dto.response.PostSummaryResponse;
 import com.jiwon.mylog.domain.post.entity.Post;
@@ -196,6 +198,23 @@ public PageResponse getPosts(Pageable pageable) {
                 postPage.getTotalElements());
     }
 
+    @Transactional(readOnly = true)
+    public PostNavigationResponse getPostNavigation(Long postId) {
+        return postRepository.findPostNavigation(postId);
+    }
+
+    @Transactional(readOnly = true)
+    public PageResponse getCategorizedPosts(Long categoryId, Long userId, Pageable pageable) {
+        Page<RelatedPostResponse> postPage = postRepository.findCategorizedPosts(categoryId, userId, pageable);
+        return PageResponse.from(
+          postPage.getContent(),
+          postPage.getNumber(),
+          postPage.getSize(),
+          postPage.getTotalPages(),
+          postPage.getTotalElements()
+        );
+    }
+
     @Cacheable(value = "post::filter", keyGenerator = "postCacheKeyGenerator")
     @Transactional(readOnly = true)
     public PageResponse getFilteredPosts(