Exception Resolver 부트 자동 예외처리

API 예외 처리 - 스프링이 제공하는 ExceptionResolver1

스프링 부트가 기본으로 제공하는 ExceptionResolver 는 다음과 같다. HandlerExceptionResolverComposite 에 다음 순서로 등록

1. ExceptionHandlerExceptionResolver
2. ResponseStatusExceptionResolver
3. DefaultHandlerExceptionResolver 우선 순위가 가장 낮다.

 

ExceptionHandlerExceptionResolver

-@ExceptionHandler 을 처리한다. API 예외 처리는 대부분 이 기능으로 해결한다. 조금 뒤에 자세히 설명한다.

 

ResponseStatusExceptionResolver

-HTTP 상태 코드를 지정해준다.
-예) @ResponseStatus(value = HttpStatus.NOT_FOUND)

 

DefaultHandlerExceptionResolver

-스프링 내부 기본 예외를 처리한다.

 

 

먼저 ResoponseStatusExceptionResolver를 사용하는 방식은 2가지로 분류된다.

 

1. 어노테이션 방식

 

package hello.exception.exception;

import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.ResponseStatus;

@ResponseStatus(code = HttpStatus.BAD_REQUEST, reason="error.bad") //BAD_REQUEST는 400이다. 더 다양한걸 보고 싶으면 클릭해서 뜯어볼 것
public class BadRequestException extends RuntimeException{


}

예제코드이다. 직접 exception을 만들어 주는데 @ResponseStatus 어노테이션을 클래스 상단에 달아준다.

    @GetMapping("/api/response-status-ex1")
    public String responseStatusEx1(){
        throw new BadRequestException();
    }

컨트롤러를 만들어 준후에 직접 만든 exception을 던져준다.

 

그런다음 호출해보면

 

 

이렇게 손 쉽게 status와 message를 바꿀 수 있는데. reason부분에 들어간 error.bad는

messages.properties 파일에서 찾을 수 있다.

 

error.bad= fail!!!

 

이렇게 넣어준다면 공통으로 사용할 수 있다.

 

2. 두번째 방식은 ResponseStatusException 예외를 던져 사용하는 것이다.

 

    @GetMapping("/api/response-status-ex2")
    public String responseStatusEx2(){
        throw new ResponseStatusException(HttpStatus.NOT_FOUND,"error.bad", new IllegalArgumentException());
    }

 

이렇게 컨트롤러 자체에서 예외를 작성해준 후 요청해보면

 

 

이렇게 직접 exception을 만들지 않아도 원하는 대로 statusd와 message를 변경할 수 있다. 다만 exception부분은 ResponseStatusException으로 들어가게 된다. 이 모든 것이 가능한 이유는 ResponseStatusExceptionResolver가 사용되기 때문이다.

/*
 * Copyright 2002-2023 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.mvc.annotation;

import java.io.IOException;

import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import org.springframework.context.MessageSource;
import org.springframework.context.MessageSourceAware;
import org.springframework.context.i18n.LocaleContextHolder;
import org.springframework.core.annotation.AnnotatedElementUtils;
import org.springframework.lang.Nullable;
import org.springframework.util.StringUtils;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.server.ResponseStatusException;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.handler.AbstractHandlerExceptionResolver;

/**
 * A {@link org.springframework.web.servlet.HandlerExceptionResolver
 * HandlerExceptionResolver} that uses the {@link ResponseStatus @ResponseStatus}
 * annotation to map exceptions to HTTP status codes.
 *
 * <p>This exception resolver is enabled by default in the
 * {@link org.springframework.web.servlet.DispatcherServlet DispatcherServlet}
 * and the MVC Java config and the MVC namespace.
 *
 * <p>As of 4.2 this resolver also looks recursively for {@code @ResponseStatus}
 * present on cause exceptions, and as of 4.2.2 this resolver supports
 * attribute overrides for {@code @ResponseStatus} in custom composed annotations.
 *
 * <p>As of 5.0 this resolver also supports {@link ResponseStatusException}.
 *
 * @author Arjen Poutsma
 * @author Rossen Stoyanchev
 * @author Sam Brannen
 * @since 3.0
 * @see ResponseStatus
 * @see ResponseStatusException
 */
public class ResponseStatusExceptionResolver extends AbstractHandlerExceptionResolver implements MessageSourceAware {

	@Nullable
	private MessageSource messageSource;


	@Override
	public void setMessageSource(MessageSource messageSource) {
		this.messageSource = messageSource;
	}


	@Override
	@Nullable
	protected ModelAndView doResolveException(
			HttpServletRequest request, HttpServletResponse response, @Nullable Object handler, Exception ex) {

		try {
			if (ex instanceof ResponseStatusException rse) {
				return resolveResponseStatusException(rse, request, response, handler);
			}

			ResponseStatus status = AnnotatedElementUtils.findMergedAnnotation(ex.getClass(), ResponseStatus.class);
			if (status != null) {
				return resolveResponseStatus(status, request, response, handler, ex);
			}

			if (ex.getCause() instanceof Exception cause) {
				return doResolveException(request, response, handler, cause);
			}
		}
		catch (Exception resolveEx) {
			if (logger.isWarnEnabled()) {
				logger.warn("Failure while trying to resolve exception [" + ex.getClass().getName() + "]", resolveEx);
			}
		}
		return null;
	}

	/**
	 * Template method that handles the {@link ResponseStatus @ResponseStatus} annotation.
	 * <p>The default implementation delegates to {@link #applyStatusAndReason}
	 * with the status code and reason from the annotation.
	 * @param responseStatus the {@code @ResponseStatus} annotation
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @param handler the executed handler, or {@code null} if none chosen at the
	 * time of the exception, e.g. if multipart resolution failed
	 * @param ex the exception
	 * @return an empty ModelAndView, i.e. exception resolved
	 */
	protected ModelAndView resolveResponseStatus(ResponseStatus responseStatus, HttpServletRequest request,
			HttpServletResponse response, @Nullable Object handler, Exception ex) throws Exception {

		int statusCode = responseStatus.code().value();
		String reason = responseStatus.reason();
		return applyStatusAndReason(statusCode, reason, response);
	}

	/**
	 * Template method that handles an {@link ResponseStatusException}.
	 * <p>The default implementation applies the headers from
	 * {@link ResponseStatusException#getHeaders()} and delegates to
	 * {@link #applyStatusAndReason} with the status code and reason from the
	 * exception.
	 * @param ex the exception
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @param handler the executed handler, or {@code null} if none chosen at the
	 * time of the exception, e.g. if multipart resolution failed
	 * @return an empty ModelAndView, i.e. exception resolved
	 * @since 5.0
	 */
	protected ModelAndView resolveResponseStatusException(ResponseStatusException ex,
			HttpServletRequest request, HttpServletResponse response, @Nullable Object handler) throws Exception {

		ex.getHeaders().forEach((name, values) -> values.forEach(value -> response.addHeader(name, value)));
		return applyStatusAndReason(ex.getStatusCode().value(), ex.getReason(), response);
	}

	/**
	 * Apply the resolved status code and reason to the response.
	 * <p>The default implementation sends a response error using
	 * {@link HttpServletResponse#sendError(int)} or
	 * {@link HttpServletResponse#sendError(int, String)} if there is a reason
	 * and then returns an empty ModelAndView.
	 * @param statusCode the HTTP status code
	 * @param reason the associated reason (may be {@code null} or empty)
	 * @param response current HTTP response
	 * @since 5.0
	 */
	protected ModelAndView applyStatusAndReason(int statusCode, @Nullable String reason, HttpServletResponse response)
			throws IOException {

		if (!StringUtils.hasLength(reason)) {
			response.sendError(statusCode);
		}
		else {
			String resolvedReason = (this.messageSource != null ?
					this.messageSource.getMessage(reason, null, reason, LocaleContextHolder.getLocale()) :
					reason);
			response.sendError(statusCode, resolvedReason);
		}
		return new ModelAndView();
	}

}

 

시간 될 때에 뜯어보면 좋을 것 같다.