Feat: 댓글 생성 API 구현 (#152)

src/main/java/com/back/domain/board/controller/CommentController.java

@@ -0,0 +1,36 @@
+package com.back.domain.board.controller;
+
+import com.back.domain.board.dto.CommentRequest;
+import com.back.domain.board.dto.CommentResponse;
+import com.back.domain.board.service.CommentService;
+import com.back.global.common.dto.RsData;
+import com.back.global.security.user.CustomUserDetails;
+import jakarta.validation.Valid;
+import lombok.RequiredArgsConstructor;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.security.core.annotation.AuthenticationPrincipal;
+import org.springframework.web.bind.annotation.*;
+
+@RestController
+@RequestMapping("/api/posts/{postId}/comments")
+@RequiredArgsConstructor
+public class CommentController implements CommentControllerDocs {
+    private final CommentService commentService;
+
+    // 댓글 생성
+    @PostMapping
+    public ResponseEntity<RsData<CommentResponse>> createComment(
+            @PathVariable Long postId,
+            @RequestBody @Valid CommentRequest request,
+            @AuthenticationPrincipal CustomUserDetails user
+    ) {
+        CommentResponse response = commentService.createComment(postId, request, user.getUserId());
+        return ResponseEntity
+                .status(HttpStatus.CREATED)
+                .body(RsData.success(
+                        "댓글이 생성되었습니다.",
+                        response
+                ));
+    }
+}

src/main/java/com/back/domain/board/controller/CommentControllerDocs.java

@@ -0,0 +1,144 @@
+package com.back.domain.board.controller;
+
+import com.back.domain.board.dto.CommentRequest;
+import com.back.domain.board.dto.CommentResponse;
+import com.back.global.common.dto.RsData;
+import com.back.global.security.user.CustomUserDetails;
+import io.swagger.v3.oas.annotations.Operation;
+import io.swagger.v3.oas.annotations.media.Content;
+import io.swagger.v3.oas.annotations.media.ExampleObject;
+import io.swagger.v3.oas.annotations.responses.ApiResponse;
+import io.swagger.v3.oas.annotations.responses.ApiResponses;
+import io.swagger.v3.oas.annotations.tags.Tag;
+import org.springframework.http.ResponseEntity;
+import org.springframework.security.core.annotation.AuthenticationPrincipal;
+import org.springframework.web.bind.annotation.*;
+
+@Tag(name = "Comment API", description = "댓글 관련 API")
+public interface CommentControllerDocs {
+
+    @Operation(
+            summary = "댓글 생성",
+            description = "로그인한 사용자가 특정 게시글에 댓글을 작성합니다."
+    )
+    @ApiResponses({
+            @ApiResponse(
+                    responseCode = "201",
+                    description = "댓글 생성 성공",
+                    content = @Content(
+                            mediaType = "application/json",
+                            examples = @ExampleObject(value = """
+                                    {
+                                      "success": true,
+                                      "code": "SUCCESS_200",
+                                      "message": "댓글이 생성되었습니다.",
+                                      "data": {
+                                        "commentId": 25,
+                                        "postId": 101,
+                                        "author": {
+                                          "id": 5,
+                                          "nickname": "홍길동"
+                                        },
+                                        "content": "좋은 글 감사합니다!",
+                                        "createdAt": "2025-09-22T11:30:00",
+                                        "updatedAt": "2025-09-22T11:30:00"
+                                      }
+                                    }
+                                    """)
+                    )
+            ),
+            @ApiResponse(
+                    responseCode = "400",
+                    description = "잘못된 요청 (필드 누락 등)",
+                    content = @Content(
+                            mediaType = "application/json",
+                            examples = @ExampleObject(value = """
+                                    {
+                                      "success": false,
+                                      "code": "COMMON_400",
+                                      "message": "잘못된 요청입니다.",
+                                      "data": null
+                                    }
+                                    """)
+                    )
+            ),
+            @ApiResponse(
+                    responseCode = "401",
+                    description = "인증 실패 (토큰 없음/잘못됨/만료)",
+                    content = @Content(
+                            mediaType = "application/json",
+                            examples = {
+                                    @ExampleObject(name = "토큰 없음", value = """
+                                            {
+                                              "success": false,
+                                              "code": "AUTH_001",
+                                              "message": "인증이 필요합니다.",
+                                              "data": null
+                                            }
+                                            """),
+                                    @ExampleObject(name = "잘못된 토큰", value = """
+                                            {
+                                              "success": false,
+                                              "code": "AUTH_002",
+                                              "message": "유효하지 않은 액세스 토큰입니다.",
+                                              "data": null
+                                            }
+                                            """),
+                                    @ExampleObject(name = "만료된 토큰", value = """
+                                            {
+                                              "success": false,
+                                              "code": "AUTH_004",
+                                              "message": "만료된 액세스 토큰입니다.",
+                                              "data": null
+                                            }
+                                            """)
+                            }
+                    )
+            ),
+            @ApiResponse(
+                    responseCode = "404",
+                    description = "존재하지 않는 사용자 또는 게시글",
+                    content = @Content(
+                            mediaType = "application/json",
+                            examples = {
+                                    @ExampleObject(name = "존재하지 않는 사용자", value = """
+                                            {
+                                              "success": false,
+                                              "code": "USER_001",
+                                              "message": "존재하지 않는 사용자입니다.",
+                                              "data": null
+                                            }
+                                            """),
+                                    @ExampleObject(name = "존재하지 않는 게시글", value = """
+                                            {
+                                              "success": false,
+                                              "code": "POST_001",
+                                              "message": "존재하지 않는 게시글입니다.",
+                                              "data": null
+                                            }
+                                            """)
+                            }
+                    )
+            ),
+            @ApiResponse(
+                    responseCode = "500",
+                    description = "서버 내부 오류",
+                    content = @Content(
+                            mediaType = "application/json",
+                            examples = @ExampleObject(value = """
+                                    {
+                                      "success": false,
+                                      "code": "COMMON_500",
+                                      "message": "서버 오류가 발생했습니다.",
+                                      "data": null
+                                    }
+                                    """)
+                    )
+            )
+    })
+    ResponseEntity<RsData<CommentResponse>> createComment(
+            @PathVariable Long postId,
+            @RequestBody CommentRequest request,
+            @AuthenticationPrincipal CustomUserDetails user
+    );
+}

src/main/java/com/back/domain/board/dto/CommentRequest.java

@@ -0,0 +1,13 @@
+package com.back.domain.board.dto;
+
+import jakarta.validation.constraints.NotBlank;
+
+/**
+ * 댓글 작성 및 수정을 위한 요청 DTO
+ *
+ * @param content   댓글 내용
+ */
+public record CommentRequest(
+        @NotBlank String content
+) {
+}

src/main/java/com/back/domain/board/dto/CommentResponse.java

@@ -0,0 +1,35 @@
+package com.back.domain.board.dto;
+
+import com.back.domain.board.entity.Comment;
+
+import java.time.LocalDateTime;
+
+/**
+ * 댓글 응답 DTO
+ *
+ * @param commentId 댓글 Id
+ * @param postId    게시글 Id
+ * @param author    작성자 정보
+ * @param content   댓글 내용
+ * @param createdAt 댓글 생성 일시
+ * @param updatedAt 댓글 수정 일시
+ */
+public record CommentResponse(
+        Long commentId,
+        Long postId,
+        AuthorResponse author,
+        String content,
+        LocalDateTime createdAt,
+        LocalDateTime updatedAt
+) {
+    public static CommentResponse from(Comment comment) {
+        return new CommentResponse(
+                comment.getId(),
+                comment.getPost().getId(),
+                AuthorResponse.from(comment.getUser()),
+                comment.getContent(),
+                comment.getCreatedAt(),
+                comment.getUpdatedAt()
+        );
+    }
+}

src/main/java/com/back/domain/board/entity/Comment.java

@@ -34,4 +34,11 @@ public class Comment extends BaseEntity {
 
     @OneToMany(mappedBy = "comment", cascade = CascadeType.ALL, orphanRemoval = true)
     private List<CommentLike> commentLikes = new ArrayList<>();
+
+    // -------------------- 생성자 --------------------
+    public Comment(Post post, User user, String content) {
+        this.post = post;
+        this.user = user;
+        this.content = content;
+    }
 }

src/main/java/com/back/domain/board/repository/CommentRepository.java

@@ -0,0 +1,9 @@
+package com.back.domain.board.repository;
+
+import com.back.domain.board.entity.Comment;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public interface CommentRepository extends JpaRepository<Comment, Long> {
+}

src/main/java/com/back/domain/board/service/CommentService.java

@@ -0,0 +1,48 @@
+package com.back.domain.board.service;
+
+import com.back.domain.board.dto.CommentRequest;
+import com.back.domain.board.dto.CommentResponse;
+import com.back.domain.board.entity.Comment;
+import com.back.domain.board.entity.Post;
+import com.back.domain.board.repository.CommentRepository;
+import com.back.domain.board.repository.PostRepository;
+import com.back.domain.user.entity.User;
+import com.back.domain.user.repository.UserRepository;
+import com.back.global.exception.CustomException;
+import com.back.global.exception.ErrorCode;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Service
+@RequiredArgsConstructor
+@Transactional
+public class CommentService {
+    private final CommentRepository commentRepository;
+    private final UserRepository userRepository;
+    private final PostRepository postRepository;
+
+    /**
+     * 댓글 생성 서비스
+     * 1. User 조회
+     * 2. Post 조회
+     * 3. Comment 생성
+     * 4. Comment 저장 및 CommentResponse 반환
+     */
+    public CommentResponse createComment(Long postId, CommentRequest request, Long userId) {
+        // User 조회
+        User user = userRepository.findById(userId)
+                .orElseThrow(() -> new CustomException(ErrorCode.USER_NOT_FOUND));
+
+        // Post 조회
+        Post post = postRepository.findById(postId)
+                .orElseThrow(() -> new CustomException(ErrorCode.POST_NOT_FOUND));
+
+        // Comment 생성
+        Comment comment = new Comment(post, user, request.content());
+
+        // Comment 저장 및 응답 반환
+        commentRepository.save(comment);
+        return CommentResponse.from(comment);
+    }
+}