[Feat] 닉네임 중복 확인 API 추가 · 중복 방지 로직 #106

src/main/java/com/indayvidual/server/common/Patterns.java

@@ -0,0 +1,10 @@
+package com.indayvidual.server.common;
+
+
+public final class Patterns {
+    private Patterns() {}
+
+    // JS/Java 공통 호환 패턴: 한글/영문/숫자/공백/_/-
+    public static final String USERNAME_JS_COMPAT =
+            "^[A-Za-z0-9 _\\-\\uAC00-\\uD7A3\\u1100-\\u11FF\\u3130-\\u318F]{2,20}$";
+}

src/main/java/com/indayvidual/server/domain/user/controller/AuthController.java

@@ -11,6 +11,7 @@
 import com.indayvidual.server.global.api.response.ApiResponse;
 import com.indayvidual.server.global.exception.GeneralException;
 import io.swagger.v3.oas.annotations.Operation;
+import io.swagger.v3.oas.annotations.responses.ApiResponses;
 import io.swagger.v3.oas.annotations.tags.Tag;
 import com.indayvidual.server.global.api.code.status.ErrorStatus;
 import jakarta.validation.Valid;
@@ -34,6 +35,11 @@ public class AuthController {
             summary = "회원가입",
             description = "이메일과 비밀번호, 이름, 전화번호를 입력하여 회원가입을 진행합니다. 이미 가입된 이메일인 경우 실패합니다."
     )
+    @ApiResponses({
+            @io.swagger.v3.oas.annotations.responses.ApiResponse(responseCode = "200", description = "가입 성공"),
+            @io.swagger.v3.oas.annotations.responses.ApiResponse(responseCode = "400", description = "요청 검증 실패"),
+            @io.swagger.v3.oas.annotations.responses.ApiResponse(responseCode = "409", description = "이메일/닉네임 중복")
+    })
     @PostMapping("/signup")
     public ResponseEntity<ApiResponse<SignupResponseDTO>> signup(@RequestBody @Valid SignupRequestDTO request) {
         SignupResponseDTO response = userAuthService.signupWithEmail(request);

src/main/java/com/indayvidual/server/domain/user/controller/UserProfileController.java

@@ -1,5 +1,6 @@
 package com.indayvidual.server.domain.user.controller;
 
+import com.indayvidual.server.common.Patterns;
 import com.indayvidual.server.domain.user.dto.request.DeleteAccountRequest;
 import com.indayvidual.server.domain.user.dto.request.UserRequestDTO;
 import com.indayvidual.server.domain.user.dto.response.SimpleMessageResponse;
@@ -15,6 +16,9 @@
 import io.swagger.v3.oas.annotations.security.SecurityRequirement;
 import io.swagger.v3.oas.annotations.tags.Tag;
 import jakarta.validation.Valid;
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.Pattern;
+import jakarta.validation.constraints.Size;
 import lombok.RequiredArgsConstructor;
 import org.springframework.http.MediaType;
 import org.springframework.http.ResponseEntity;
@@ -51,6 +55,28 @@ public ResponseEntity<ApiResponse<UserResponseDTO.Profile>> getMyProfile(
         return ResponseEntity.ok(ApiResponse.onSuccess(profile));
     }
 
+    @Operation(
+            summary = "닉네임 중복 확인",
+            description = "입력한 닉네임이 사용 가능한지 확인합니다. (본인 닉네임은 중복으로 간주하지 않음)"
+    )
+    @ApiResponses({
+            @io.swagger.v3.oas.annotations.responses.ApiResponse(responseCode = "200", description = "사용 가능 여부 반환"),
+            @io.swagger.v3.oas.annotations.responses.ApiResponse(responseCode = "400", description = "형식 오류"),
+            @io.swagger.v3.oas.annotations.responses.ApiResponse(responseCode = "401", description = "인증 실패")
+    })
+    @GetMapping("/username/check")
+    public ResponseEntity<ApiResponse<Boolean>> checkUsername(
+            @AuthenticationPrincipal JwtUserPrincipal principal,
+            @Parameter(description = "확인할 닉네임", example = "감자도리")
+            @RequestParam @NotBlank(message = "username은 필수입니다.")
+            @Size(min = 2, max = 20, message = "닉네임은 2~20자여야 합니다.")
+            @Pattern(regexp = Patterns.USERNAME_JS_COMPAT, message = "닉네임은 한글/영문/숫자/공백/[_-]만 허용합니다.")
+            String username
+    ) {
+                boolean available = userProfileService.isUsernameAvailable(username, principal.userId());
+                return ResponseEntity.ok(ApiResponse.onSuccess(available));
+    }
+
     @Operation(summary = "닉네임 변경", description = "재인증 토큰 검증 후 닉네임을 변경합니다.")
     @ApiResponses({
             @io.swagger.v3.oas.annotations.responses.ApiResponse(responseCode = "200", description = "변경 성공"),

src/main/java/com/indayvidual/server/domain/user/dto/request/SignupRequestDTO.java

@@ -28,6 +28,9 @@ public class SignupRequestDTO {
 
     @Schema(description = "사용자 이름", example = "박성준", requiredMode = Schema.RequiredMode.REQUIRED)
     @NotBlank(message = "이름은 필수입니다.")
+    @Size(min = 2, max = 20, message = "닉네임은 2~20자여야 합니다.")
+    @Pattern(regexp = com.indayvidual.server.common.Patterns.USERNAME_JS_COMPAT,
+                         message = "닉네임은 한글/영문/숫자/공백/[_-]만 허용합니다.")
     private String username;
 
     @Schema(description = "전화번호(선택)", example = "010-1234-5678")

src/main/java/com/indayvidual/server/domain/user/entity/User.java

@@ -42,6 +42,8 @@ public class User extends BaseEntity {
 
 	private String email;
 	private String password;  // (소셜 로그인 시 null)
+
+	@Column(unique = true)
 	private String username;
 	private String phone_number;
 

src/main/java/com/indayvidual/server/domain/user/repository/UserRepository.java

@@ -14,4 +14,7 @@ public interface UserRepository extends JpaRepository<User, Long> {
     boolean existsByEmail(String email);
 
     Optional<User> findByEmailAndStatus(String email, Status status);
+
+    boolean existsByUsernameIgnoreCase(String username);
+    boolean existsByUsernameIgnoreCaseAndIdNot(String username, Long id);
 }

src/main/java/com/indayvidual/server/domain/user/service/UserService/UserAuthServiceImpl.java

@@ -39,9 +39,15 @@ public class UserAuthServiceImpl implements UserAuthService {
     @Override
     public SignupResponseDTO signupWithEmail(SignupRequestDTO request) {
 
+        // 1) 이메일 중복
         if (userRepository.existsByEmail(request.getEmail())) {
             throw new GeneralException(ErrorStatus.AUTH_EMAIL_DUPLICATED);
         }
+        // 2) 닉네임 중복 (대소문자 무시)
+        if (userRepository.existsByUsernameIgnoreCase(request.getUsername())) {
+            throw new GeneralException(ErrorStatus.AUTH_USERNAME_DUPLICATED);
+        }
+
         String encodedPassword = passwordEncoder.encode(request.getPassword());
 
         User user = User.builder()

src/main/java/com/indayvidual/server/domain/user/service/UserService/UserProfileService.java

@@ -54,7 +54,31 @@ public UserResponseDTO.Profile getMyProfile(Long userId) {
     public void updateUsername(Long userId, String newUsername) {
         User user = userRepository.findById(userId)
                 .orElseThrow(() -> new GeneralException(ErrorStatus.MYPAGE_USER_NOT_FOUND));
-        user.changeUsername(newUsername);
+        String target = newUsername == null ? "" : newUsername.trim();
+        if (target.isEmpty()) throw new GeneralException(ErrorStatus._BAD_REQUEST);
+        // 동일 닉네임(대소문자/공백 무시)인 경우 변경 스킵
+        if (user.getUsername() != null && user.getUsername().trim().equalsIgnoreCase(target)) {
+            return;
+        }
+        // 타 유저가 사용 중이면 차단
+        boolean exists = userRepository.existsByUsernameIgnoreCaseAndIdNot(target, userId);
+        if (exists) throw new GeneralException(ErrorStatus.MYPAGE_USERNAME_DUPLICATED);
+        user.changeUsername(target);
+    }
+
+    @Transactional(readOnly = true)
+    public boolean isUsernameAvailable(String candidate, Long currentUserId) {
+        String target = candidate == null ? "" : candidate.trim();
+        if (target.isEmpty()) return false;
+        if (currentUserId != null) {
+            // 본인 닉네임은 중복으로 간주하지 않음
+            boolean sameAsMine = userRepository.findById(currentUserId)
+                    .map(u -> u.getUsername() != null && u.getUsername().trim().equalsIgnoreCase(target))
+                    .orElse(false);
+            if (sameAsMine) return true;
+            return !userRepository.existsByUsernameIgnoreCaseAndIdNot(target, currentUserId);
+        }
+        return !userRepository.existsByUsernameIgnoreCase(target);
     }
 
     public void updatePassword(Long userId, String currentPassword, String newPassword) {

src/main/java/com/indayvidual/server/global/api/code/status/ErrorStatus.java

@@ -53,6 +53,7 @@ public enum ErrorStatus implements BaseErrorCode {
     AUTH_USER_NOT_FOUND(HttpStatus.UNAUTHORIZED, "AUTH4015", "존재하지 않는 사용자입니다."),
     AUTH_OAUTH_INVALID_TOKEN(HttpStatus.UNAUTHORIZED, "AUTH4016", "소셜 액세스 토큰이 유효하지 않습니다."),
     AUTH_OAUTH_PROVIDER_ERROR(HttpStatus.BAD_GATEWAY, "AUTH5021", "소셜 인증 제공자와의 통신에 실패했습니다."),
+    AUTH_USERNAME_DUPLICATED(HttpStatus.CONFLICT, "AUTH4092", "이미 사용 중인 닉네임입니다."),
 
     // ===== EMAIL VERIFICATION =====
     EMAIL_RESEND_COOLDOWN(HttpStatus.TOO_MANY_REQUESTS, "EMAIL4290", "요청이 너무 잦습니다. 잠시 후 다시 시도해 주세요."),
@@ -77,6 +78,7 @@ public enum ErrorStatus implements BaseErrorCode {
     MYPAGE_IMAGE_TOO_LARGE(HttpStatus.PAYLOAD_TOO_LARGE, "MYPAGE4130", "이미지 용량이 허용 범위를 초과했습니다."),
     MYPAGE_IMAGE_UPLOAD_FAILED(HttpStatus.BAD_GATEWAY, "MYPAGE5020", "이미지 업로드에 실패했습니다."),
     MYPAGE_PASSWORD_NOT_SUPPORTED(HttpStatus.CONFLICT, "MYPAGE4091", "비밀번호를 변경할 수 없는 계정입니다."),
+    MYPAGE_USERNAME_DUPLICATED(HttpStatus.CONFLICT, "MYPAGE4092", "이미 사용 중인 닉네임입니다."),
 
     // 계정 관련
     USER_NOT_FOUND(HttpStatus.NOT_FOUND, "USER4041", "사용자를 찾을 수 없습니다."),