✨ Feat: 닉네임 중복 확인 기능 구현

src/main/java/com/dodo/backend/common/config/SecurityConfig.java

@@ -77,6 +77,7 @@ public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
                                 "/auth/reissue",
                                 "/auth/devices",
                                 "/auth/reissue/devices",
+                                "/users/nickname/check",
                                 "/ws-dodo"
                         ).permitAll()
                         .requestMatchers(
@@ -164,4 +165,4 @@ private void sendErrorResponse(HttpServletResponse response, UserErrorCode error
 
         response.getWriter().write(objectMapper.writeValueAsString(errorBody));
     }
-}
+}

src/main/java/com/dodo/backend/user/controller/UserController.java

@@ -6,6 +6,7 @@
 import com.dodo.backend.user.dto.request.UserRequest.UserUpdateRequest;
 import com.dodo.backend.user.dto.request.UserRequest.WithdrawalRequest;
 import com.dodo.backend.user.dto.response.UserResponse;
+import com.dodo.backend.user.dto.response.UserResponse.NicknameCheckResponse;
 import com.dodo.backend.user.dto.response.UserResponse.UserInfoResponse;
 import com.dodo.backend.user.dto.response.UserResponse.UserRegisterResponse;
 import com.dodo.backend.user.dto.response.UserResponse.UserUpdateResponse;
@@ -36,6 +37,38 @@ public class UserController {
 
     private final UserService userService;
 
+    /**
+     * 회원가입 전 입력한 닉네임이 이미 사용 중인지 확인합니다.
+     *
+     * @param nickname 중복 여부를 확인할 닉네임
+     * @return 닉네임과 중복 여부가 포함된 응답 DTO
+     */
+    @Operation(summary = "닉네임 중복 확인", description = "입력한 닉네임의 중복 여부를 확인합니다.")
+    @ApiResponses(value = {
+            @ApiResponse(responseCode = "200", description = "닉네임 중복 확인이 완료되었습니다.",
+                    content = @Content(schema = @Schema(implementation = NicknameCheckResponse.class))),
+            @ApiResponse(responseCode = "400", description = "닉네임 형식이 올바르지 않습니다.",
+                    content = @Content(mediaType = "application/json",
+                            schema = @Schema(implementation = ErrorResponse.class),
+                            examples = @ExampleObject(name = "400 Bad Request", value = "{\"status\": 400, \"message\": \"닉네임 형식이 올바르지 않습니다.\"}"))),
+            @ApiResponse(responseCode = "404", description = "사용자를 찾을 수 없습니다.",
+                    content = @Content(mediaType = "application/json",
+                            schema = @Schema(implementation = ErrorResponse.class),
+                            examples = @ExampleObject(name = "404 Not Found", value = "{\"status\": 404, \"message\": \"사용자를 찾을 수 없습니다.\"}"))),
+            @ApiResponse(responseCode = "500", description = "서버 내부 오류가 발생했습니다.",
+                    content = @Content(mediaType = "application/json",
+                            schema = @Schema(implementation = ErrorResponse.class),
+                            examples = @ExampleObject(name = "500 Internal Server Error", value = "{\"status\": 500, \"message\": \"서버 내부 오류가 발생했습니다.\"}")))
+    })
+    @GetMapping("/nickname/check")
+    public ResponseEntity<NicknameCheckResponse> checkNicknameDuplication(
+            @RequestParam String nickname) {
+
+        log.info("닉네임 중복 확인 요청 - nickname: {}", nickname);
+
+        return ResponseEntity.ok(userService.checkNicknameDuplication(nickname));
+    }
+
     /**
      * 회원가입 프로세스의 마지막 단계로, 추가 정보를 입력받아 계정을 활성화합니다.
      * <p>
@@ -291,4 +324,4 @@ public ResponseEntity<String> updateNotification(
 
         return ResponseEntity.ok("알림 수신 설정을 성공적으로 변경했습니다.");
     }
-}
+}

src/main/java/com/dodo/backend/user/dto/response/UserResponse.java

@@ -154,4 +154,31 @@ public static UserUpdateResponse toDto(User user, String message, String nicknam
                     .build();
         }
     }
-}
+
+    /**
+     * 닉네임 중복 확인 결과를 반환하는 응답 DTO입니다.
+     */
+    @Getter
+    @Builder
+    @AllArgsConstructor
+    @Schema(description = "닉네임 중복 확인 응답")
+    public static class NicknameCheckResponse {
+
+        @Schema(description = "응답 메시지", example = "닉네임 중복 확인이 완료되었습니다.")
+        private String message;
+
+        @Schema(description = "확인한 닉네임", example = "도도")
+        private String nickname;
+
+        @Schema(description = "닉네임 중복 여부", example = "false")
+        private Boolean duplicated;
+
+        public static NicknameCheckResponse toDto(String nickname, Boolean duplicated) {
+            return NicknameCheckResponse.builder()
+                    .message("닉네임 중복 확인이 완료되었습니다.")
+                    .nickname(nickname)
+                    .duplicated(duplicated)
+                    .build();
+        }
+    }
+}

src/main/java/com/dodo/backend/user/service/UserService.java

@@ -3,6 +3,7 @@
 import com.dodo.backend.user.dto.request.UserRequest.UserRegisterRequest;
 import com.dodo.backend.user.dto.request.UserRequest.UserUpdateRequest;
 import com.dodo.backend.user.dto.response.UserResponse.UserInfoResponse;
+import com.dodo.backend.user.dto.response.UserResponse.NicknameCheckResponse;
 import com.dodo.backend.user.dto.response.UserResponse.UserRegisterResponse;
 import com.dodo.backend.user.dto.response.UserResponse.UserUpdateResponse;
 import com.dodo.backend.user.entity.User;
@@ -77,6 +78,14 @@ public interface UserService {
      */
     void updateNotification(UUID userId, Boolean enabled);
 
+    /**
+     * 닉네임 중복 여부를 확인합니다.
+     *
+     * @param nickname 확인할 닉네임
+     * @return 닉네임 중복 확인 결과 응답 DTO
+     */
+    NicknameCheckResponse checkNicknameDuplication(String nickname);
+
     /**
      * ID로 사용자 엔티티를 조회합니다.
      * <p>
@@ -88,4 +97,4 @@ public interface UserService {
      */
     User getUserById(UUID userId);
 
-}
+}

src/main/java/com/dodo/backend/user/service/UserServiceImpl.java

@@ -6,6 +6,7 @@
 import com.dodo.backend.user.dto.request.UserRequest;
 import com.dodo.backend.user.dto.request.UserRequest.UserRegisterRequest;
 import com.dodo.backend.user.dto.response.UserResponse.UserInfoResponse;
+import com.dodo.backend.user.dto.response.UserResponse.NicknameCheckResponse;
 import com.dodo.backend.user.dto.response.UserResponse.UserRegisterResponse;
 import com.dodo.backend.user.dto.response.UserResponse.UserUpdateResponse;
 import com.dodo.backend.user.entity.User;
@@ -36,6 +37,10 @@
 @Slf4j
 public class UserServiceImpl implements UserService {
 
+    private static final String NICKNAME_PATTERN = "^[가-힣a-zA-Z0-9 ]*$";
+    private static final int NICKNAME_MIN_LENGTH = 2;
+    private static final int NICKNAME_MAX_LENGTH = 10;
+
     private final UserRepository userRepository;
     private final UserMapper userMapper;
     private final JwtTokenProvider jwtTokenProvider;
@@ -281,6 +286,35 @@ public void updateNotification(UUID userId, Boolean enabled) {
         userMapper.updateNotificationStatus(userId, enabled);
     }
 
+    /**
+     * 회원가입 전 입력한 닉네임의 형식을 검증하고 중복 여부를 확인합니다.
+     * <p>
+     * 닉네임은 2자 이상 10자 이하이며, 한글, 영문, 숫자, 공백만 사용할 수 있습니다.
+     *
+     * @param nickname 중복 여부를 확인할 닉네임
+     * @return 닉네임과 중복 여부가 포함된 응답 DTO
+     * @throws UserException 닉네임이 비어 있거나 형식이 올바르지 않은 경우
+     */
+    @Transactional(readOnly = true)
+    @Override
+    public NicknameCheckResponse checkNicknameDuplication(String nickname) {
+        if (nickname == null || nickname.isBlank()) {
+            throw new UserException(INVALID_REQUEST);
+        }
+
+        if (nickname.length() < NICKNAME_MIN_LENGTH || nickname.length() > NICKNAME_MAX_LENGTH) {
+            throw new UserException(INVALID_REQUEST);
+        }
+
+        if (!nickname.matches(NICKNAME_PATTERN)) {
+            throw new UserException(INVALID_REQUEST);
+        }
+
+        boolean duplicated = userRepository.existsByNickname(nickname);
+
+        return NicknameCheckResponse.toDto(nickname, duplicated);
+    }
+
     /**
      * ID로 사용자 엔티티 조회 (예외 처리 포함)
      */
@@ -290,4 +324,4 @@ public User getUserById(UUID userId) {
         return userRepository.findById(userId)
                 .orElseThrow(() -> new UserException(USER_NOT_FOUND));
     }
-}
+}

src/test/java/com/dodo/backend/user/controller/UserControllerTest.java

@@ -0,0 +1,49 @@
+package com.dodo.backend.user.controller;
+
+import com.dodo.backend.user.dto.response.UserResponse.NicknameCheckResponse;
+import com.dodo.backend.user.service.UserService;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.springframework.http.ResponseEntity;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.BDDMockito.given;
+import static org.mockito.Mockito.verify;
+
+/**
+ * {@link UserController}의 HTTP 요청 처리 로직을 검증하는 테스트 클래스입니다.
+ */
+@ExtendWith(MockitoExtension.class)
+class UserControllerTest {
+
+    @Mock
+    private UserService userService;
+
+    /**
+     * 닉네임 중복 확인 요청 시 200 상태 코드와 중복 확인 결과를 반환하는지 검증합니다.
+     */
+    @Test
+    @DisplayName("닉네임 중복 확인 성공")
+    void checkNicknameDuplicationSuccessTest() {
+        //given
+        UserController userController = new UserController(userService);
+        String nickname = "도도";
+        NicknameCheckResponse serviceResponse = NicknameCheckResponse.toDto(nickname, false);
+
+        given(userService.checkNicknameDuplication(nickname)).willReturn(serviceResponse);
+
+        //when
+        ResponseEntity<NicknameCheckResponse> response = userController.checkNicknameDuplication(nickname);
+
+        //then
+        assertThat(response.getStatusCode().value()).isEqualTo(200);
+        assertThat(response.getBody()).isNotNull();
+        assertThat(response.getBody().getNickname()).isEqualTo(nickname);
+        assertThat(response.getBody().getDuplicated()).isFalse();
+
+        verify(userService).checkNicknameDuplication(nickname);
+    }
+}