feature: 게시물 단건 조회 구현

src/main/java/daybyquest/post/application/GetPostService.java

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+package daybyquest.post.application;
+
+import daybyquest.post.dto.response.PostResponse;
+import daybyquest.post.query.PostDao;
+import daybyquest.post.query.PostData;
+import daybyquest.user.query.Profile;
+import daybyquest.user.query.ProfileDao;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Service
+public class GetPostService {
+
+    private final PostDao postDao;
+
+    private final ProfileDao profileDao;
+
+    public GetPostService(final PostDao postDao, final ProfileDao profileDao) {
+        this.postDao = postDao;
+        this.profileDao = profileDao;
+    }
+
+    @Transactional(readOnly = true)
+    public PostResponse invoke(final Long loginId, final Long postId) {
+        final PostData postData = postDao.getByPostId(loginId, postId);
+        final Profile profile = profileDao.getById(loginId, postData.getUserId());
+        return PostResponse.of(postData, profile);
+    }
+}

src/main/java/daybyquest/post/dto/response/PostResponse.java

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+package daybyquest.post.dto.response;
+
+import daybyquest.image.vo.Image;
+import daybyquest.post.query.PostData;
+import daybyquest.user.dto.response.ProfileResponse;
+import daybyquest.user.query.Profile;
+import java.time.LocalDateTime;
+import java.util.List;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+
+@Getter
+@NoArgsConstructor
+public class PostResponse {
+
+    private ProfileResponse author;
+
+    private Long id;
+
+    private String content;
+
+    private LocalDateTime updatedAt;
+
+    private boolean liked;
+
+    private List<String> images;
+
+    public PostResponse(final ProfileResponse author, final Long id, final String content,
+            final LocalDateTime updatedAt, final boolean liked,
+            final List<String> images) {
+        this.author = author;
+        this.id = id;
+        this.content = content;
+        this.updatedAt = updatedAt;
+        this.liked = liked;
+        this.images = images;
+    }
+
+    public static PostResponse of(final PostData postData, final Profile profile) {
+        return new PostResponse(ProfileResponse.of(profile), postData.getId(), postData.getContent(),
+                postData.getUpdatedAt(), postData.isLiked(),
+                postData.getImages().stream().map(Image::getImageIdentifier).toList()
+        );
+    }
+}

src/main/java/daybyquest/post/presentation/PostQueryApi.java

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+package daybyquest.post.presentation;
+
+import daybyquest.auth.Authorization;
+import daybyquest.auth.UserId;
+import daybyquest.post.application.GetPostService;
+import daybyquest.post.dto.response.PostResponse;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+public class PostQueryApi {
+
+    private final GetPostService getPostService;
+
+    public PostQueryApi(final GetPostService getPostService) {
+        this.getPostService = getPostService;
+    }
+
+    @GetMapping("/post/{postId}")
+    @Authorization
+    public ResponseEntity<PostResponse> getPost(@UserId final Long loginId, @PathVariable final Long postId) {
+        final PostResponse response = getPostService.invoke(loginId, postId);
+        return ResponseEntity.ok(response);
+    }
+}

src/main/java/daybyquest/post/query/PostDao.java

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+package daybyquest.post.query;
+
+public interface PostDao {
+
+    PostData getByPostId(final Long userId, final Long postId);
+}

src/main/java/daybyquest/post/query/PostDaoQuerydslImpl.java

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+package daybyquest.post.query;
+
+import static daybyquest.image.vo.QImage.image;
+import static daybyquest.like.domain.QPostLike.postLike;
+import static daybyquest.post.domain.QPost.post;
+
+import com.querydsl.core.types.Projections;
+import com.querydsl.jpa.JPAExpressions;
+import com.querydsl.jpa.impl.JPAQueryFactory;
+import daybyquest.global.error.exception.NotExistPostException;
+import daybyquest.image.vo.Image;
+import java.util.List;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public class PostDaoQuerydslImpl implements PostDao {
+
+    private final JPAQueryFactory factory;
+
+    public PostDaoQuerydslImpl(final JPAQueryFactory factory) {
+        this.factory = factory;
+    }
+
+    @Override
+    public PostData getByPostId(final Long userId, final Long postId) {
+        final PostData postData = factory.select(Projections.constructor(PostData.class,
+                        post.userId,
+                        post.id,
+                        post.content,
+                        post.updatedAt,
+                        JPAExpressions.selectFrom(postLike)
+                                .where(postLike.userId.eq(userId).and(postLike.postId.eq(postId)))
+                                .exists()))
+                .from(post)
+                .where(post.id.eq(postId))
+                .fetchOne();
+        if (postData == null) {
+            throw new NotExistPostException();
+        }
+        final List<Image> images = factory.select(image)
+                .from(post)
+                .leftJoin(post.images, image)
+                .where(post.id.eq(postId))
+                .fetch();
+        postData.setImages(images);
+        return postData;
+    }
+}

src/main/java/daybyquest/post/query/PostData.java

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+package daybyquest.post.query;
+
+import daybyquest.image.vo.Image;
+import java.time.LocalDateTime;
+import java.util.List;
+import lombok.Getter;
+
+@Getter
+public class PostData {
+
+    private final Long userId;
+
+    private final Long id;
+
+    private final String content;
+
+    private final LocalDateTime updatedAt;
+
+    private final boolean liked;
+
+    private List<Image> images;
+
+    public PostData(final Long userId, final Long id, final String content, final LocalDateTime updatedAt,
+            final boolean liked) {
+        this.userId = userId;
+        this.id = id;
+        this.content = content;
+        this.updatedAt = updatedAt;
+        this.liked = liked;
+    }
+
+    public void setImages(final List<Image> images) {
+        this.images = images;
+    }
+}