refactor: 패키지 구조 및 코드 스타일 개선

.coderabbit.yaml

@@ -64,9 +64,8 @@ reviews:
         - Indentation: use spaces (no tabs), tab width = 4 spaces; files must end with Unix LF newline. (Team adaptation)
         - Maximum line length: 120 characters.
         - Imports: single-class imports only; allow wildcard for static imports; group imports with blank lines between sections.
-        - Assignment operators (`=`, `+=`, `-=`, etc.): always one space before and after; on line breaks, place the operator at the start of the next line.
+        - Operators: always one space before and after; on line breaks, place operators at the start of the next line (commas stay at end of line, dots at start of new line).
         - Lambda expressions: omit parentheses for a single parameter; surround `->` with spaces (`param -> expression`); use braces and explicit `return` for multi-statement bodies; choose short, clear parameter names.
-        - In multi-line expressions, place operators and ternary separators at end-of-line.
         - Prefer Java 21 standard APIs over Guava.
         - Do not annotate immutable local variables with `final` unless required for an inner class.
         - Allow the `var` keyword when the value is a cast `null`.
@@ -90,6 +89,47 @@ reviews:
         - Prioritize correctness of assertions, coverage of edge cases, and clear test naming/documentation.
         - Be lenient on style and minor optimizations in tests.
 
+    - path: "**/application/usecase/**/*.java"
+      instructions: |
+        - Use cases must be defined as interfaces with a single public method representing one business operation.
+        - Method names should clearly express the business intent (e.g., `create`, `delete`, `accept`, `send`).
+        - Avoid multiple unrelated operations in a single use case interface.
+        - Keep method signatures simple and focused; use Command or Query objects for complex parameters.
+
+    - path: "**/application/command/**/*.java"
+      instructions: |
+        - Commands must be immutable records.
+        - All input validation must occur in the compact constructor.
+        - Normalize inputs (e.g., `strip()` for strings) in the compact constructor before validation.
+        - Provide sensible defaults for optional fields (e.g., `Set.of()` for empty collections).
+        - Throw `BusinessException` with appropriate `ErrorCode` for validation failures.
+        - Commands should represent write operations; avoid query-related fields unless necessary for the write operation.
+
+    - path: "**/application/query/**/*.java"
+      instructions: |
+        - Queries must be immutable records.
+        - All input validation must occur in the compact constructor.
+        - Validate pagination parameters (e.g., `size > 0`, `size <= 100`, `lastId > 0`).
+        - Throw `BusinessException` with appropriate `ErrorCode` for validation failures.
+        - Queries should only contain parameters needed for read operations.
+
+    - path: "**/application/result/**/*.java"
+      instructions: |
+        - Results must be immutable records.
+        - Use static factory methods named `from` to convert from domain or query results.
+        - Results should only expose data needed by the presentation layer; avoid leaking domain internals.
+        - Prefer composition over deeply nested structures.
+
+    - path: "**/application/service/**/*Service.java"
+      instructions: |
+        - Services must be annotated with `@Service` and implement one or more use case interfaces.
+        - Follow the Read/Write separation pattern: use separate classes for read operations (e.g., `FriendReadService`) and write operations (e.g., `FriendWriteService`).
+        - Write operations must be annotated with `@Transactional`.
+        - Read operations should use `@Transactional(readOnly = true)` when appropriate.
+        - Services should orchestrate domain logic, not contain it; delegate business rules to domain entities.
+        - Throw `BusinessException` with appropriate `ErrorCode` for business rule violations.
+        - Avoid direct manipulation of entities; prefer calling domain methods.
+
   abort_on_close: true
   disable_cache: false
 

.rules/checkstyle-rules.xml

@@ -356,7 +356,13 @@ The following rules in the Naver coding convention cannot be checked by this con
                      value="[space-after-comma-semicolon]: ''{0}'' is not followed by whitespace."/>
         </module>
         <module name="NoWhitespaceBefore">
-            <property name="tokens" value="COMMA,SEMI"/>
+            <property name="tokens" value="COMMA"/>
+            <message key="ws.preceded"
+                     value="[space-after-comma-semicolon] ''{0}'' is preceded with whitespace."/>
+        </module>
+        <module name="NoWhitespaceBefore">
+            <property name="tokens" value="SEMI"/>
+            <property name="allowLineBreaks" value="true"/>
             <message key="ws.preceded"
                      value="[space-after-comma-semicolon] ''{0}'' is preceded with whitespace."/>
         </module>

src/main/java/queuing/core/CoreApplication.java

@@ -7,9 +7,7 @@
 @SpringBootApplication
 @ConfigurationPropertiesScan
 public class CoreApplication {
-
-	public static void main(String[] args) {
-		SpringApplication.run(CoreApplication.class, args);
-	}
-
+    public static void main(String[] args) {
+        SpringApplication.run(CoreApplication.class, args);
+    }
 }

src/main/java/queuing/core/friend/application/query/GetListFriendQuery.java

@@ -0,0 +1,28 @@
+package queuing.core.friend.application.query;
+
+import queuing.core.global.exception.BusinessException;
+import queuing.core.global.exception.ErrorCode;
+
+public record GetListFriendQuery(
+    String userSlug,
+    Long lastId,
+    int size
+) {
+    public GetListFriendQuery {
+        if (userSlug == null || userSlug.isBlank()) {
+            throw new BusinessException(ErrorCode.COMMON_INVALID_INPUT);
+        }
+        userSlug = userSlug.strip();
+
+        if (lastId != null && lastId <= 0) {
+            throw new BusinessException(ErrorCode.COMMON_INVALID_INPUT);
+        }
+
+        if (size <= 0) {
+            throw new BusinessException(ErrorCode.COMMON_INVALID_INPUT);
+        }
+        if (size > 100) {
+            throw new BusinessException(ErrorCode.COMMON_INVALID_INPUT);
+        }
+    }
+}

src/main/java/queuing/core/friend/application/dto/FriendSummary.java → src/main/java/queuing/core/friend/application/result/FriendSummary.java

@@ -1,4 +1,4 @@
-package queuing.core.friend.application.dto;
+package queuing.core.friend.application.result;
 
 import queuing.core.user.domain.entity.User;
 

src/main/java/queuing/core/friend/application/service/FriendReadService.java

@@ -6,8 +6,9 @@
 import org.springframework.transaction.annotation.Transactional;
 
 import lombok.RequiredArgsConstructor;
-import queuing.core.friend.application.dto.FriendSummary;
-import queuing.core.friend.application.dto.GetFriendListCommand;
+
+import queuing.core.friend.application.query.GetListFriendQuery;
+import queuing.core.friend.application.result.FriendSummary;
 import queuing.core.friend.application.usecase.GetFriendListUseCase;
 import queuing.core.friend.domain.entity.Friend;
 import queuing.core.friend.domain.repository.FriendRepository;
@@ -21,21 +22,24 @@
 @RequiredArgsConstructor
 @Transactional(readOnly = true)
 public class FriendReadService implements GetFriendListUseCase {
-
-    private final UserRepository userRepository;
     private final FriendRepository friendRepository;
+    private final UserRepository userRepository;
 
     @Override
-    public SliceResult<FriendSummary> getFriendList(GetFriendListCommand command) {
-        User user = userRepository.findBySlug(command.userSlug())
+    public SliceResult<FriendSummary> getFriendList(GetListFriendQuery query) {
+        User user = userRepository.findBySlug(query.userSlug())
             .orElseThrow(() -> new BusinessException(ErrorCode.USER_NOT_FOUND));
 
-        SliceResult<Friend> friends = friendRepository.findFriendsByUserId(user.getId(), command.lastId(), command.size());
+        SliceResult<Friend> result = friendRepository.findFriendsByUserId(
+            user.getId(),
+            query.lastId(),
+            query.size()
+        );
 
-        List<FriendSummary> summaries = friends.items().stream()
+        List<FriendSummary> summaries = result.items().stream()
             .map(friend -> FriendSummary.from(friend.getCounterpart(user)))
             .toList();
 
-        return SliceResult.of(summaries, friends.hasNext());
+        return SliceResult.of(summaries, result.hasNext());
     }
-}
+}

src/main/java/queuing/core/friend/application/service/FriendWriteService.java

@@ -32,19 +32,11 @@ public void sendRequest(String requesterSlug, String targetSlug) {
         User target = userRepository.findBySlug(targetSlug)
             .orElseThrow(() -> new BusinessException(ErrorCode.USER_NOT_FOUND));
 
-        if (requester.equals(target)) {
-            throw new BusinessException(ErrorCode.FRIEND_INVALID_REQUEST);
-        }
-
         if (friendRepository.findRelationship(requester, target).isPresent()) {
             throw new BusinessException(ErrorCode.FRIEND_ALREADY_EXISTS);
         }
 
-        Friend friend = Friend.builder()
-            .requester(requester)
-            .receiver(target)
-            .status(FriendStatus.PENDING)
-            .build();
+        Friend friend = Friend.createRequest(requester, target);
 
         friendRepository.save(friend);
     }
@@ -58,15 +50,7 @@ public void acceptRequest(String userSlug, Long requestId) {
         Friend friend = friendRepository.findById(requestId)
             .orElseThrow(() -> new BusinessException(ErrorCode.FRIEND_REQUEST_NOT_FOUND));
 
-        if (!friend.getReceiver().equals(user)) {
-            throw new BusinessException(ErrorCode.FRIEND_INVALID_REQUEST);
-        }
-
-        if (friend.getStatus() != FriendStatus.PENDING) {
-            throw new BusinessException(ErrorCode.FRIEND_INVALID_REQUEST);
-        }
-
-        friend.updateStatus(FriendStatus.ACCEPTED);
+        friend.accept(user);
     }
 
     @Override

src/main/java/queuing/core/friend/application/usecase/DeleteFriendUseCase.java

@@ -2,4 +2,4 @@
 
 public interface DeleteFriendUseCase {
     void deleteFriend(String userSlug, String targetSlug);
-}
+}

src/main/java/queuing/core/friend/application/usecase/GetFriendListUseCase.java

@@ -1,9 +1,9 @@
 package queuing.core.friend.application.usecase;
 
-import queuing.core.friend.application.dto.FriendSummary;
-import queuing.core.friend.application.dto.GetFriendListCommand;
+import queuing.core.friend.application.query.GetListFriendQuery;
+import queuing.core.friend.application.result.FriendSummary;
 import queuing.core.global.dto.SliceResult;
 
 public interface GetFriendListUseCase {
-    SliceResult<FriendSummary> getFriendList(GetFriendListCommand command);
-}
+    SliceResult<FriendSummary> getFriendList(GetListFriendQuery query);
+}

src/main/java/queuing/core/friend/application/usecase/SendFriendRequestUseCase.java

@@ -2,4 +2,4 @@
 
 public interface SendFriendRequestUseCase {
     void sendRequest(String requesterSlug, String targetSlug);
-}
+}

src/main/java/queuing/core/friend/domain/entity/Friend.java

@@ -1,6 +1,7 @@
 package queuing.core.friend.domain.entity;
 
 import java.time.Instant;
+import java.util.Objects;
 
 import jakarta.persistence.Column;
 import jakarta.persistence.Entity;
@@ -24,6 +25,9 @@
 import lombok.Builder;
 import lombok.Getter;
 import lombok.NoArgsConstructor;
+
+import queuing.core.global.exception.BusinessException;
+import queuing.core.global.exception.ErrorCode;
 import queuing.core.user.domain.entity.User;
 
 @Entity
@@ -76,4 +80,44 @@ public User getCounterpart(User user) {
         }
         return requester;
     }
+
+    public static Friend createRequest(User requester, User receiver) {
+        if (requester.equals(receiver)) {
+            throw new BusinessException(ErrorCode.FRIEND_INVALID_REQUEST);
+        }
+        return Friend.builder()
+            .requester(requester)
+            .receiver(receiver)
+            .status(FriendStatus.PENDING)
+            .build();
+    }
+
+    public void accept(User user) {
+        if (!this.receiver.equals(user)) {
+            throw new BusinessException(ErrorCode.FRIEND_INVALID_REQUEST);
+        }
+
+        if (this.status != FriendStatus.PENDING) {
+            throw new BusinessException(ErrorCode.FRIEND_INVALID_REQUEST);
+        }
+
+        this.status = FriendStatus.ACCEPTED;
+    }
+
+    @Override
+    public final boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (!(obj instanceof Friend friend)) {
+            return false;
+        }
+
+        return this.getId() != null && Objects.equals(this.getId(), friend.getId());
+    }
+
+    @Override
+    public final int hashCode() {
+        return Objects.hash(this.getId());
+    }
 }

src/main/java/queuing/core/friend/domain/repository/FriendRepository.java

@@ -18,10 +18,9 @@ public interface FriendRepository extends JpaRepository<Friend, Long>, FriendRep
 
     Optional<Friend> findByRequesterAndReceiver(User requester, User receiver);
 
-    // Find a relationship in either direction
-    @Query("SELECT f FROM Friend f WHERE (f.requester = :user1 AND f.receiver = :user2) OR (f.requester = :user2 AND f.receiver = :user1)")
+    @Query("SELECT f FROM Friend f WHERE (f.requester = :user1 AND f.receiver = :user2) "
+        + "OR (f.requester = :user2 AND f.receiver = :user1)")
     Optional<Friend> findRelationship(@Param("user1") User user1, @Param("user2") User user2);
 
-    // Find pending requests received by user
     Page<Friend> findByReceiverAndStatus(User receiver, FriendStatus status, Pageable pageable);
 }

src/main/java/queuing/core/friend/infrastructure/querydsl/FriendRepositoryImpl.java

@@ -8,6 +8,7 @@
 import com.querydsl.jpa.impl.JPAQueryFactory;
 
 import lombok.RequiredArgsConstructor;
+
 import queuing.core.friend.domain.entity.Friend;
 import queuing.core.friend.domain.entity.FriendStatus;
 import queuing.core.friend.domain.entity.QFriend;
@@ -25,7 +26,7 @@ public SliceResult<Friend> findFriendsByUserId(Long userId, Long lastId, int siz
 
         BooleanExpression isFriend = (friend.requester.id.eq(userId).or(friend.receiver.id.eq(userId)))
             .and(friend.status.eq(FriendStatus.ACCEPTED));
-        
+
         BooleanExpression lessThanId = (lastId != null) ? friend.id.lt(lastId) : null;
 
         List<Friend> friends = query.selectFrom(friend)
@@ -44,4 +45,4 @@ public SliceResult<Friend> findFriendsByUserId(Long userId, Long lastId, int siz
 
         return SliceResult.of(friends, hasNext);
     }
-}
+}

src/main/java/queuing/core/friend/presentation/controller/FriendController.java

@@ -14,8 +14,8 @@
 
 import lombok.RequiredArgsConstructor;
 
-import queuing.core.friend.application.dto.FriendSummary;
-import queuing.core.friend.application.dto.GetFriendListCommand;
+import queuing.core.friend.application.query.GetListFriendQuery;
+import queuing.core.friend.application.result.FriendSummary;
 import queuing.core.friend.application.usecase.DeleteFriendUseCase;
 import queuing.core.friend.application.usecase.GetFriendListUseCase;
 import queuing.core.friend.presentation.response.FriendResponse;
@@ -50,7 +50,7 @@ public ResponseEntity<ResponseBody<ListFriendResponse>> getFriends(
         @RequestParam(defaultValue = "20") int size
     ) {
         SliceResult<FriendSummary> result = getFriendListUseCase.getFriendList(
-            new GetFriendListCommand(principal.getUsername(), lastId, size)
+            new GetListFriendQuery(principal.getUsername(), lastId, size)
         );
 
         List<FriendResponse> items = result.items().stream()

src/main/java/queuing/core/friend/presentation/request/SendFriendRequest.java

@@ -5,4 +5,5 @@
 public record SendFriendRequest(
     @NotBlank(message = "친구 추가할 대상을 입력해주세요.")
     String targetSlug
-) {}
+) {
+}

src/main/java/queuing/core/friend/presentation/response/FriendResponse.java

@@ -1,6 +1,6 @@
 package queuing.core.friend.presentation.response;
 
-import queuing.core.friend.application.dto.FriendSummary;
+import queuing.core.friend.application.result.FriendSummary;
 
 public record FriendResponse(
     Long id,