@ExceptionHandler Springboot의 자동 예외처리

@ExceptionHandler

스프링은 API 예외 처리 문제를 해결하기 위해 @ExceptionHandler 라는 애노테이션을 사용하는 매우 편리한 예외 처리 기능을 제공하는데, 이것이 바로 ExceptionHandlerExceptionResolver 이다. 스프링은 ExceptionHandlerExceptionResolver 를 기본으로 제공하고, 기본으로 제공하는 ExceptionResolver 중에 우선순위도 가장 높다. 실무에서 API 예외 처리는 대부분 이 기능을 사용한다

 

 

 

컨트롤러에서 오류가 터지면 먼저 디스패처에 다시 간다음 ExceptionHandler가 호출 된다. 그 중 가장 먼저 호출되는 것은 ExceptionHandlerExceptionResolver이다. 

 

/*
 * 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.method.annotation;

import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

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

import org.springframework.aop.support.AopUtils;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.http.HttpStatusCode;
import org.springframework.http.converter.ByteArrayHttpMessageConverter;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter;
import org.springframework.lang.Nullable;
import org.springframework.ui.ModelMap;
import org.springframework.web.accept.ContentNegotiationManager;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.context.request.ServletWebRequest;
import org.springframework.web.method.ControllerAdviceBean;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.method.annotation.ExceptionHandlerMethodResolver;
import org.springframework.web.method.annotation.MapMethodProcessor;
import org.springframework.web.method.annotation.ModelMethodProcessor;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.HandlerMethodArgumentResolverComposite;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite;
import org.springframework.web.method.support.ModelAndViewContainer;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.View;
import org.springframework.web.servlet.handler.AbstractHandlerMethodExceptionResolver;
import org.springframework.web.servlet.mvc.support.RedirectAttributes;
import org.springframework.web.servlet.support.RequestContextUtils;

/**
 * An {@link AbstractHandlerMethodExceptionResolver} that resolves exceptions
 * through {@code @ExceptionHandler} methods.
 *
 * <p>Support for custom argument and return value types can be added via
 * {@link #setCustomArgumentResolvers} and {@link #setCustomReturnValueHandlers}.
 * Or alternatively to re-configure all argument and return value types use
 * {@link #setArgumentResolvers} and {@link #setReturnValueHandlers(List)}.
 *
 * @author Rossen Stoyanchev
 * @author Juergen Hoeller
 * @author Sebastien Deleuze
 * @since 3.1
 */
public class ExceptionHandlerExceptionResolver extends AbstractHandlerMethodExceptionResolver
		implements ApplicationContextAware, InitializingBean {

	@Nullable
	private List<HandlerMethodArgumentResolver> customArgumentResolvers;

	@Nullable
	private HandlerMethodArgumentResolverComposite argumentResolvers;

	@Nullable
	private List<HandlerMethodReturnValueHandler> customReturnValueHandlers;

	@Nullable
	private HandlerMethodReturnValueHandlerComposite returnValueHandlers;

	private final List<HttpMessageConverter<?>> messageConverters = new ArrayList<>();

	private ContentNegotiationManager contentNegotiationManager = new ContentNegotiationManager();

	private final List<Object> responseBodyAdvice = new ArrayList<>();

	@Nullable
	private ApplicationContext applicationContext;

	private final Map<Class<?>, ExceptionHandlerMethodResolver> exceptionHandlerCache =
			new ConcurrentHashMap<>(64);

	private final Map<ControllerAdviceBean, ExceptionHandlerMethodResolver> exceptionHandlerAdviceCache =
			new LinkedHashMap<>();


	/**
	 * Provide resolvers for custom argument types. Custom resolvers are ordered
	 * after built-in ones. To override the built-in support for argument
	 * resolution use {@link #setArgumentResolvers} instead.
	 */
	public void setCustomArgumentResolvers(@Nullable List<HandlerMethodArgumentResolver> argumentResolvers) {
		this.customArgumentResolvers = argumentResolvers;
	}

	/**
	 * Return the custom argument resolvers, or {@code null}.
	 */
	@Nullable
	public List<HandlerMethodArgumentResolver> getCustomArgumentResolvers() {
		return this.customArgumentResolvers;
	}

	/**
	 * Configure the complete list of supported argument types thus overriding
	 * the resolvers that would otherwise be configured by default.
	 */
	public void setArgumentResolvers(@Nullable List<HandlerMethodArgumentResolver> argumentResolvers) {
		if (argumentResolvers == null) {
			this.argumentResolvers = null;
		}
		else {
			this.argumentResolvers = new HandlerMethodArgumentResolverComposite();
			this.argumentResolvers.addResolvers(argumentResolvers);
		}
	}

	/**
	 * Return the configured argument resolvers, or possibly {@code null} if
	 * not initialized yet via {@link #afterPropertiesSet()}.
	 */
	@Nullable
	public HandlerMethodArgumentResolverComposite getArgumentResolvers() {
		return this.argumentResolvers;
	}

	/**
	 * Provide handlers for custom return value types. Custom handlers are
	 * ordered after built-in ones. To override the built-in support for
	 * return value handling use {@link #setReturnValueHandlers}.
	 */
	public void setCustomReturnValueHandlers(@Nullable List<HandlerMethodReturnValueHandler> returnValueHandlers) {
		this.customReturnValueHandlers = returnValueHandlers;
	}

	/**
	 * Return the custom return value handlers, or {@code null}.
	 */
	@Nullable
	public List<HandlerMethodReturnValueHandler> getCustomReturnValueHandlers() {
		return this.customReturnValueHandlers;
	}

	/**
	 * Configure the complete list of supported return value types thus
	 * overriding handlers that would otherwise be configured by default.
	 */
	public void setReturnValueHandlers(@Nullable List<HandlerMethodReturnValueHandler> returnValueHandlers) {
		if (returnValueHandlers == null) {
			this.returnValueHandlers = null;
		}
		else {
			this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite();
			this.returnValueHandlers.addHandlers(returnValueHandlers);
		}
	}

	/**
	 * Return the configured handlers, or possibly {@code null} if not
	 * initialized yet via {@link #afterPropertiesSet()}.
	 */
	@Nullable
	public HandlerMethodReturnValueHandlerComposite getReturnValueHandlers() {
		return this.returnValueHandlers;
	}

	/**
	 * Set the message body converters to use.
	 * <p>These converters are used to convert from and to HTTP requests and responses.
	 */
	public void setMessageConverters(List<HttpMessageConverter<?>> messageConverters) {
		this.messageConverters.clear();
		this.messageConverters.addAll(messageConverters);
	}

	/**
	 * Return the configured message body converters.
	 */
	public List<HttpMessageConverter<?>> getMessageConverters() {
		return this.messageConverters;
	}

	/**
	 * Set the {@link ContentNegotiationManager} to use to determine requested media types.
	 * If not set, the default constructor is used.
	 */
	public void setContentNegotiationManager(ContentNegotiationManager contentNegotiationManager) {
		this.contentNegotiationManager = contentNegotiationManager;
	}

	/**
	 * Return the configured {@link ContentNegotiationManager}.
	 */
	public ContentNegotiationManager getContentNegotiationManager() {
		return this.contentNegotiationManager;
	}

	/**
	 * Add one or more components to be invoked after the execution of a controller
	 * method annotated with {@code @ResponseBody} or returning {@code ResponseEntity}
	 * but before the body is written to the response with the selected
	 * {@code HttpMessageConverter}.
	 */
	public void setResponseBodyAdvice(@Nullable List<ResponseBodyAdvice<?>> responseBodyAdvice) {
		if (responseBodyAdvice != null) {
			this.responseBodyAdvice.addAll(responseBodyAdvice);
		}
	}

	@Override
	public void setApplicationContext(@Nullable ApplicationContext applicationContext) {
		this.applicationContext = applicationContext;
	}

	@Nullable
	public ApplicationContext getApplicationContext() {
		return this.applicationContext;
	}


	@Override
	public void afterPropertiesSet() {
		// Do this first, it may add ResponseBodyAdvice beans
		initExceptionHandlerAdviceCache();
		initMessageConverters();

		if (this.argumentResolvers == null) {
			List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
			this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
		}
		if (this.returnValueHandlers == null) {
			List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
			this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
		}
	}

	private void initMessageConverters() {
		if (!this.messageConverters.isEmpty()) {
			return;
		}
		this.messageConverters.add(new ByteArrayHttpMessageConverter());
		this.messageConverters.add(new StringHttpMessageConverter());
		this.messageConverters.add(new AllEncompassingFormHttpMessageConverter());
	}

	private void initExceptionHandlerAdviceCache() {
		if (getApplicationContext() == null) {
			return;
		}

		List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
		for (ControllerAdviceBean adviceBean : adviceBeans) {
			Class<?> beanType = adviceBean.getBeanType();
			if (beanType == null) {
				throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean);
			}
			ExceptionHandlerMethodResolver resolver = new ExceptionHandlerMethodResolver(beanType);
			if (resolver.hasExceptionMappings()) {
				this.exceptionHandlerAdviceCache.put(adviceBean, resolver);
			}
			if (ResponseBodyAdvice.class.isAssignableFrom(beanType)) {
				this.responseBodyAdvice.add(adviceBean);
			}
		}

		if (logger.isDebugEnabled()) {
			int handlerSize = this.exceptionHandlerAdviceCache.size();
			int adviceSize = this.responseBodyAdvice.size();
			if (handlerSize == 0 && adviceSize == 0) {
				logger.debug("ControllerAdvice beans: none");
			}
			else {
				logger.debug("ControllerAdvice beans: " +
						handlerSize + " @ExceptionHandler, " + adviceSize + " ResponseBodyAdvice");
			}
		}
	}

	/**
	 * Return an unmodifiable Map with the {@link ControllerAdvice @ControllerAdvice}
	 * beans discovered in the ApplicationContext. The returned map will be empty if
	 * the method is invoked before the bean has been initialized via
	 * {@link #afterPropertiesSet()}.
	 */
	public Map<ControllerAdviceBean, ExceptionHandlerMethodResolver> getExceptionHandlerAdviceCache() {
		return Collections.unmodifiableMap(this.exceptionHandlerAdviceCache);
	}

	/**
	 * Return the list of argument resolvers to use including built-in resolvers
	 * and custom resolvers provided via {@link #setCustomArgumentResolvers}.
	 */
	protected List<HandlerMethodArgumentResolver> getDefaultArgumentResolvers() {
		List<HandlerMethodArgumentResolver> resolvers = new ArrayList<>();

		// Annotation-based argument resolution
		resolvers.add(new SessionAttributeMethodArgumentResolver());
		resolvers.add(new RequestAttributeMethodArgumentResolver());

		// Type-based argument resolution
		resolvers.add(new ServletRequestMethodArgumentResolver());
		resolvers.add(new ServletResponseMethodArgumentResolver());
		resolvers.add(new RedirectAttributesMethodArgumentResolver());
		resolvers.add(new ModelMethodProcessor());

		// Custom arguments
		if (getCustomArgumentResolvers() != null) {
			resolvers.addAll(getCustomArgumentResolvers());
		}

		// Catch-all
		resolvers.add(new PrincipalMethodArgumentResolver());

		return resolvers;
	}

	/**
	 * Return the list of return value handlers to use including built-in and
	 * custom handlers provided via {@link #setReturnValueHandlers}.
	 */
	protected List<HandlerMethodReturnValueHandler> getDefaultReturnValueHandlers() {
		List<HandlerMethodReturnValueHandler> handlers = new ArrayList<>();

		// Single-purpose return value types
		handlers.add(new ModelAndViewMethodReturnValueHandler());
		handlers.add(new ModelMethodProcessor());
		handlers.add(new ViewMethodReturnValueHandler());
		handlers.add(new HttpEntityMethodProcessor(
				getMessageConverters(), this.contentNegotiationManager, this.responseBodyAdvice));

		// Annotation-based return value types
		handlers.add(new ServletModelAttributeMethodProcessor(false));
		handlers.add(new RequestResponseBodyMethodProcessor(
				getMessageConverters(), this.contentNegotiationManager, this.responseBodyAdvice));

		// Multi-purpose return value types
		handlers.add(new ViewNameMethodReturnValueHandler());
		handlers.add(new MapMethodProcessor());

		// Custom return value types
		if (getCustomReturnValueHandlers() != null) {
			handlers.addAll(getCustomReturnValueHandlers());
		}

		// Catch-all
		handlers.add(new ServletModelAttributeMethodProcessor(true));

		return handlers;
	}

	@Override
	protected boolean hasGlobalExceptionHandlers() {
		return !this.exceptionHandlerAdviceCache.isEmpty();
	}

	/**
	 * Find an {@code @ExceptionHandler} method and invoke it to handle the raised exception.
	 */
	@Override
	@Nullable
	protected ModelAndView doResolveHandlerMethodException(HttpServletRequest request,
			HttpServletResponse response, @Nullable HandlerMethod handlerMethod, Exception exception) {

		ServletInvocableHandlerMethod exceptionHandlerMethod = getExceptionHandlerMethod(handlerMethod, exception);
		if (exceptionHandlerMethod == null) {
			return null;
		}

		if (this.argumentResolvers != null) {
			exceptionHandlerMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
		}
		if (this.returnValueHandlers != null) {
			exceptionHandlerMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
		}

		ServletWebRequest webRequest = new ServletWebRequest(request, response);
		ModelAndViewContainer mavContainer = new ModelAndViewContainer();

		ArrayList<Throwable> exceptions = new ArrayList<>();
		try {
			if (logger.isDebugEnabled()) {
				logger.debug("Using @ExceptionHandler " + exceptionHandlerMethod);
			}
			// Expose causes as provided arguments as well
			Throwable exToExpose = exception;
			while (exToExpose != null) {
				exceptions.add(exToExpose);
				Throwable cause = exToExpose.getCause();
				exToExpose = (cause != exToExpose ? cause : null);
			}
			Object[] arguments = new Object[exceptions.size() + 1];
			exceptions.toArray(arguments);  // efficient arraycopy call in ArrayList
			arguments[arguments.length - 1] = handlerMethod;
			exceptionHandlerMethod.invokeAndHandle(webRequest, mavContainer, arguments);
		}
		catch (Throwable invocationEx) {
			// Any other than the original exception (or a cause) is unintended here,
			// probably an accident (e.g. failed assertion or the like).
			if (!exceptions.contains(invocationEx) && logger.isWarnEnabled()) {
				logger.warn("Failure in @ExceptionHandler " + exceptionHandlerMethod, invocationEx);
			}
			// Continue with default processing of the original exception...
			return null;
		}

		if (mavContainer.isRequestHandled()) {
			return new ModelAndView();
		}
		else {
			ModelMap model = mavContainer.getModel();
			HttpStatusCode status = mavContainer.getStatus();
			ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model, status);
			mav.setViewName(mavContainer.getViewName());
			if (!mavContainer.isViewReference()) {
				mav.setView((View) mavContainer.getView());
			}
			if (model instanceof RedirectAttributes redirectAttributes) {
				Map<String, ?> flashAttributes = redirectAttributes.getFlashAttributes();
				RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
			}
			return mav;
		}
	}

	/**
	 * Find an {@code @ExceptionHandler} method for the given exception. The default
	 * implementation searches methods in the class hierarchy of the controller first
	 * and if not found, it continues searching for additional {@code @ExceptionHandler}
	 * methods assuming some {@linkplain ControllerAdvice @ControllerAdvice}
	 * Spring-managed beans were detected.
	 * @param handlerMethod the method where the exception was raised (may be {@code null})
	 * @param exception the raised exception
	 * @return a method to handle the exception, or {@code null} if none
	 */
	@Nullable
	protected ServletInvocableHandlerMethod getExceptionHandlerMethod(
			@Nullable HandlerMethod handlerMethod, Exception exception) {

		Class<?> handlerType = null;

		if (handlerMethod != null) {
			// Local exception handler methods on the controller class itself.
			// To be invoked through the proxy, even in case of an interface-based proxy.
			handlerType = handlerMethod.getBeanType();
			ExceptionHandlerMethodResolver resolver = this.exceptionHandlerCache.computeIfAbsent(
					handlerType, ExceptionHandlerMethodResolver::new);
			Method method = resolver.resolveMethod(exception);
			if (method != null) {
				return new ServletInvocableHandlerMethod(handlerMethod.getBean(), method, this.applicationContext);
			}
			// For advice applicability check below (involving base packages, assignable types
			// and annotation presence), use target class instead of interface-based proxy.
			if (Proxy.isProxyClass(handlerType)) {
				handlerType = AopUtils.getTargetClass(handlerMethod.getBean());
			}
		}

		for (Map.Entry<ControllerAdviceBean, ExceptionHandlerMethodResolver> entry : this.exceptionHandlerAdviceCache.entrySet()) {
			ControllerAdviceBean advice = entry.getKey();
			if (advice.isApplicableToBeanType(handlerType)) {
				ExceptionHandlerMethodResolver resolver = entry.getValue();
				Method method = resolver.resolveMethod(exception);
				if (method != null) {
					return new ServletInvocableHandlerMethod(advice.resolveBean(), method, this.applicationContext);
				}
			}
		}

		return null;
	}

}

 

이 클래스는 매우 복잡하다. 먼저 얻어갈 수 있는 정보로는 @ExceptionHandler 태그가 있는 것을 먼저 호출 해준다.

 

package hello.exception.api;

import hello.exception.exception.UserException;
import hello.exception.exhandler.ErrorResult;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@Slf4j
@RestController
public class ApiExceptionV2Controller {

    @ExceptionHandler(IllegalArgumentException.class)
    public ErrorResult illegalExHandler(IllegalArgumentException e){
        log.error("[exceptionHandler] ex",e);
        return new ErrorResult("BAD", e.getMessage());
    }

    @GetMapping("/api2/members/{id}")
    public ApiExceptionController.MemberDto getMember(@PathVariable("id")String id){
        if(id.equals("ex")){
            throw new RuntimeException("잘못된 사용자");
        }
        if(id.equals("bad")){
            throw new IllegalArgumentException("잘못된 입력 값");
        }
        if(id.equals("user-ex")){
            throw new UserException("사용자 오류");
        }
        return new ApiExceptionController.MemberDto(id, "hello" + id);
    }

    @Data
    @AllArgsConstructor
    static class MemberDto {
        private String memberId;
        private String name;
    }
}

package hello.exception.exhandler;

import lombok.AllArgsConstructor;
import lombok.Data;

@Data
@AllArgsConstructor
public class ErrorResult {
    private String code;
    private String message;
}

 

호출 할 시에 결과값으로 표시되는 것이 보일 것이다.

 

하지만, 문제가 되는 것은 status가 200으로 뜬다는 것이다. 왜냐하면 현재 로직으로보면 Exception이 터졌을 때에 return으로 정상적인 값을 반환했다. 그러므로 응답 자체가 정상이 되는 것이다. 

 

@ResponseStatus(HttpStatus.BAD_REQUEST)
@ExceptionHandler(IllegalArgumentException.class)
public ErrorResult illegalExHandler(IllegalArgumentException e){
    log.error("[exceptionHandler] ex",e);
    return new ErrorResult("BAD", e.getMessage());
}

 

그럴 때엔 @ResponseStatus 어노테이션을 이용해서 반환 값을 지정해 준다.

 

 

그럼 이렇게 status가 변경 된 것을 볼 수 있다.

 

혹은 다른 방식으로 던질 수 있다.

 

@ExceptionHandler //매개변수로 Exception을 두면 같은 것으로 인식하며 생략할 수 있다.
public ResponseEntity<ErrorResult> userExHandler(UserException e){
    log.error("[exceptionHandler] ex", e);
    ErrorResult errorResult = new ErrorResult("User-EX", e.getMessage());
    return new ResponseEntity(errorResult, HttpStatus.BAD_REQUEST);
}

 

 

위의 IllegalArgumentException 과 UserException의 자식이 있을 경우 해당 메소드를 타게 된다.

하지만 그 외의 오류들은 

@ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
@ExceptionHandler
public ErrorResult exHandler(Exception e){
    log.error("[exceptionHandler] ex", e);
    return new ErrorResult("EX", "내부오류");
}

 

이렇게 전체 Exception으로 잡아주면 그 외의 오류는 모두 이 메소드를 타게 된다.

 

****저 클래스 안에서만 예외처리가 되니 주의하기 바란다

 

 

@ExceptionHandler(부모예외.class) public String 부모예외처리()(부모예외 e) {}

@ExceptionHandler(자식예외.class) public String 자식예외처리()(자식예외 e) {}

 

이 상황이라면 자식예외 처리가 먼저 된다.

 

 @ExceptionHandler({AException.class, BException.class})
  public String ex(Exception e) {

      log.info("exception e", e);
  }

 

이렇게 다양한 예외를 가지는 것도 가능하다.

 

파리미터와 응답

@ExceptionHandler 에는 마치 스프링의 컨트롤러의 파라미터 응답처럼 다양한 파라미터와 응답을 지정할 수 있다.
자세한 파라미터와 응답은 다음 공식 메뉴얼을 참고하자.

https://docs.spring.io/spring-framework/docs/current/reference/html/web.html#mvc-ann-exceptionhandler-args

 

 

@ResponseStatus(HttpStatus.BAD_REQUEST)
@ExceptionHandler(IllegalArgumentException.class)
public String illegalExHandler(IllegalArgumentException e){
    log.error("[exceptionHandler] ex",e);
    return "error/400";
}

 

이렇게 view로 반환도 가능하다.

 

@ResponseStatus(HttpStatus.BAD_REQUEST)
  @ExceptionHandler(IllegalArgumentException.class)
  public ErrorResult illegalExHandle(IllegalArgumentException e) {
         log.error("[exceptionHandle] ex", e);
       return new ErrorResult("BAD", e.getMessage());
  }

실행 흐름

-컨트롤러를 호출한 결과 IllegalArgumentException 예외가 컨트롤러 밖으로 던져진다.

-예외가 발생했으로 ExceptionResolver 가 작동한다.

-가장 우선순위가 높은 ExceptionHandlerExceptionResolver 가 실행된다.

-ExceptionHandlerExceptionResolver 는 해당 컨트롤러에 IllegalArgumentException 을 처리할 수 있는 @ExceptionHandler 가 있는지 확인한다.

-illegalExHandle() 를 실행한다.

-@RestController 이므로 illegalExHandle() 에도 @ResponseBody 가 적용된다. 따라서 HTTP 컨버터가 사용되고, 응답이 다음과 같은 JSON으로 반환된다.

-@ResponseStatus(HttpStatus.BAD_REQUEST) 를 지정했으므로 HTTP 상태 코드 400으로 응답한다.

 

 @ExceptionHandler
  public ResponseEntity<ErrorResult> userExHandle(UserException e) {
      log.error("[exceptionHandle] ex", e);
      ErrorResult errorResult = new ErrorResult("USER-EX", e.getMessage());
      return new ResponseEntity<>(errorResult, HttpStatus.BAD_REQUEST);
}

 

-@ExceptionHandler 에 예외를 지정하지 않으면 해당 메서드 파라미터 예외를 사용한다. 여기서는 UserException 을 사용한다.

- ResponseEntity 를 사용해서 HTTP 메시지 바디에 직접 응답한다. 물론 HTTP 컨버터가 사용된다.

ResponseEntity 를 사용하면 HTTP 응답 코드를 프로그래밍해서 동적으로 변경할 수 있다. 앞서 살펴본 @ResponseStatus 는 애노테이션이므로 HTTP 응답 코드를 동적으로 변경할 수 없다.

 

@ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
  @ExceptionHandler
  public ErrorResult exHandle(Exception e) {
log.error("[exceptionHandle] ex", e); return new ErrorResult("EX", "내부 오류");
}

 

- thrownewRuntimeException("잘못된 사용자")이코드가실행되면서,컨트롤러밖으로 RuntimeException 이 던져진다.

- RuntimeException 은 Exception 의 자식 클래스이다. 따라서 이 메서드가 호출된다. @ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR) 로 HTTP 상태 코드를 500으로 응답한다.

 

 

HTML 오류 화면
다음과 같이 ModelAndView 를 사용해서 오류 화면(HTML)을 응답하는데 사용할 수도 있다.

@ExceptionHandler(ViewException.class)
  public ModelAndView ex(ViewException e) {
      log.info("exception e", e);
      return new ModelAndView("error");
  }