효율적인 예외 처리를 위한 커스텀 에러 코드 구축하기

@Getter
public abstract class AbstractHttpException extends RuntimeException {
    private final HttpStatus status;          // HTTP 상태 코드
    private final String errorCode;           // 에러 코드
    private final String message;             // 에러 메시지
    private final String errorLog;            // 상세 에러 로그 (선택적)

    // 필수 정보만을 포함한 생성자
    public AbstractHttpException(HttpStatus status, String errorCode, String message) {
        super(message);
        this.status = status;
        this.errorCode = errorCode;
        this.message = message;
        this.errorLog = null;
    }

    // 상세 에러 로그를 추가하는 생성자
    public AbstractHttpException(HttpStatus status, String errorCode, String message, String errorLog) {
        super(message);
        this.status = status;
        this.errorCode = errorCode;
        this.message = message;
        this.errorLog = errorLog;
    }
}

public interface DomainException {
    String getErrorCode();
    String getMessage();
    Class<?> getAClass();
}

@Getter
public enum CouponCodeException implements DomainException {
    COUPON_NOT_FOUND("CCD-001", "존재하지 않는 쿠폰입니다.", NotFoundException.class),
    ALREADY_REGISTERED("CCD-002", "이미 등록된 쿠폰 코드입니다.", BadRequestException.class),
    ...
    ;

    private final String errorCode;
    private final String message;
    private final Class<?> aClass;

    CouponCodeException(String errorCode, String message, Class<?> aClass) {
        this.errorCode = errorCode;
        this.message = message;
        this.aClass = aClass;
    }
}

public class NotFoundException extends AbstractHttpException {

	// 기본 에러코드 생성자
    public NotFoundException(String errorCode, String message) {
        super(HttpStatus.NOT_FOUND, errorCode, message);
    }

	// 상세 에러코드 생성자(민감한 정보를 포함하여 서버에서만 확인할 수 있도록 하기위해 사용)
    public NotFoundException(String errorCode, String message, String errorLog) {
        super(HttpStatus.NOT_FOUND, errorCode, message, errorLog);
    }
}

public class HttpExceptionCreator {
    // 동적 예외 생성 메서드
    private static <T> T createInstance(Class<? extends T> clazz, Object... args) {
        Constructor<? extends T>[] constructorArray = (Constructor<? extends T>[]) clazz.getDeclaredConstructors();
        for (Constructor<? extends T> constructor : constructorArray) {
            try {
                return constructor.newInstance(args);
            } catch (Exception ignored) {
                // 생성자 호출 실패 시 다음 생성자로 시도
            }
        }
        throw new RuntimeException("Failed to create HttpException instance");
    }

    // 다양한 예외 생성 메서드 오버로딩
    public static AbstractHttpException create(DomainException e) {
        return (AbstractHttpException) createInstance(e.getAClass(), e.getErrorCode(), e.getMessage());
    }

    public static AbstractHttpException create(DomainException e, String errorLog) {
        return (AbstractHttpException) createInstance(e.getAClass(), e.getErrorCode(), e.getMessage(), errorLog);
    }
}

@RequiredArgsConstructor
public class HttpExceptionHandlerFilter extends OncePerRequestFilter {
    @Override
    protected void doFilterInternal(
             HttpServletRequest request, HttpServletResponse response, FilterChain filterChain
    ) throws ServletException, IOException {
        try {
            filterChain.doFilter(request, response);
        }
        catch (AbstractHttpException e) {
            createdExceptionResponse(response, e);
        }
    }

    private void createdExceptionResponse(HttpServletResponse response, AbstractHttpException e) {
        log.error("[" + e.getErrorCode() + "] : " + e.getErrorLog());

        response.setContentType(MediaType.APPLICATION_JSON_VALUE);
        response.setStatus(e.getStatus().value());
        try (OutputStream os = response.getOutputStream()) {
            ObjectMapper objectMapper = new ObjectMapper();
            objectMapper.writeValue(os, HttpExceptionResponse.builder()
                    .errorCode(e.getErrorCode())
                    .message(e.getMessage())
                    .build()
            );
            os.flush();
        } catch (IOException ioException) {
            throw new RuntimeException("Failed to create HttpExceptionResponse", ioException);
        }
    }
}

{
  "errorCode": "CCD-001",
  "message": "존재하지 않는 쿠폰입니다.",
  "timeStamp": "2024-06-18T15:45:23"
}

@Getter
@Builder
public class HttpExceptionResponse {
    private final String errorCode;
    private final String message;
    private final String timeStamp = LocalDateTime.now().toString();

    public static ResponseEntity<HttpExceptionResponse> toResponseEntity(AbstractHttpException e) {
        return ResponseEntity
                .status(e.getStatus())
                .headers(e.getHttpHeaders())
                .body(
                        HttpExceptionResponse.builder()
                                .errorCode(e.getErrorCode())
                                .message(e.getMessage())
                                .build()
                );
    }
}

@Configuration
@RequiredArgsConstructor
@EnableWebSecurity
@EnableMethodSecurity(prePostEnabled = true)
public class WebSecurityConfig {
    ...
    ...
    @Bean
    public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
        http
			// ... 여러 설정들
            .addFilterBefore(new HttpExceptionHandlerFilter());
        return http.build();
    }
}

public class DiscountCouponService {
	...
	...

	public void applyDiscountCoupon(Long userCouponId) {
	    UserCoupon userCoupon = userCouponRepository.findById(userCouponId)
	            .orElseThrow(() -> HttpExceptionCreator.create(COUPON_NOT_FOUND, "UserCouponId: " + userCouponId));
	        ...
	        ...
	        ...
	}
}

{
  "errorCode": "CCD-001",
  "message": "존재하지 않는 쿠폰입니다.",
  "timeStamp": "2024-06-18T15:45:23"
}