全局异常处理

demo展示

@Slf4j
@RestControllerAdvice
public class GlobalExceptionAdvice {

    @ExceptionHandler(RuntimeException.class)
    public R<Void> handleNotPermissionException(RuntimeException e, HttpServletRequest request) {
        String requestURI = request.getRequestURI();
        log.error("请求地址'{}',异常信息'{}'", requestURI, e.getMessage());
        e.printStackTrace();
        return R.fail(e.getMessage());
    }
}

RestControllerAdvice是ControllerAdvice和ResponseBody的混合注解。

原理解析

系统初始化

WebMvcConfigurationSupport会初始化HandlerExceptionResolver

	@Bean
	public HandlerExceptionResolver handlerExceptionResolver(
			@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager) {
		List<HandlerExceptionResolver> exceptionResolvers = new ArrayList<>();
		configureHandlerExceptionResolvers(exceptionResolvers);
		if (exceptionResolvers.isEmpty()) {
			addDefaultHandlerExceptionResolvers(exceptionResolvers, contentNegotiationManager);
		}
		extendHandlerExceptionResolvers(exceptionResolvers);
		HandlerExceptionResolverComposite composite = new HandlerExceptionResolverComposite();
		composite.setOrder(0);
		composite.setExceptionResolvers(exceptionResolvers);
		return composite;
	}

WebMvcConfigurationSupport#addDefaultHandlerExceptionResolvers，该方法创建了ExceptionHandlerExceptionResolver，执行afterPropertiesSet方法。

	protected final void addDefaultHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers,
			ContentNegotiationManager mvcContentNegotiationManager) {

		ExceptionHandlerExceptionResolver exceptionHandlerResolver = createExceptionHandlerExceptionResolver();
		exceptionHandlerResolver.setContentNegotiationManager(mvcContentNegotiationManager);
		exceptionHandlerResolver.setMessageConverters(getMessageConverters());
		exceptionHandlerResolver.setCustomArgumentResolvers(getArgumentResolvers());
		exceptionHandlerResolver.setCustomReturnValueHandlers(getReturnValueHandlers());
		if (jackson2Present) {
			exceptionHandlerResolver.setResponseBodyAdvice(
					Collections.singletonList(new JsonViewResponseBodyAdvice()));
		}
		if (this.applicationContext != null) {
			exceptionHandlerResolver.setApplicationContext(this.applicationContext);
		}
		exceptionHandlerResolver.afterPropertiesSet();
		exceptionResolvers.add(exceptionHandlerResolver);

		ResponseStatusExceptionResolver responseStatusResolver = new ResponseStatusExceptionResolver();
		responseStatusResolver.setMessageSource(this.applicationContext);
		exceptionResolvers.add(responseStatusResolver);

		exceptionResolvers.add(new DefaultHandlerExceptionResolver());
	}

ExceptionHandlerExceptionResolver#afterPropertiesSet，执行initExceptionHandlerAdviceCache

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

		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);
		}
	}

ExceptionHandlerExceptionResolver#initExceptionHandlerAdviceCache，对于所有获取到的ControllerAdviceBean再次封装成ExceptionHandlerMethodResolver，判断是否存在hasExceptionMappings，加入到exceptionHandlerAdviceCache

	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");
			}
		}
	}

ExceptionHandlerMethodResolver构造方法。寻找带有ExceptionHandler注解的方法，获取注解的value值，即异常处理器处理的异常类。将异常信息和方法的对应关系保存下来。

	public ExceptionHandlerMethodResolver(Class<?> handlerType) {
		for (Method method : MethodIntrospector.selectMethods(handlerType, EXCEPTION_HANDLER_METHODS)) {
			for (Class<? extends Throwable> exceptionType : detectExceptionMappings(method)) {
				addExceptionMapping(exceptionType, method);
			}
		}
	}

	private void addExceptionMapping(Class<? extends Throwable> exceptionType, Method method) {
		Method oldMethod = this.mappedMethods.put(exceptionType, method);
		if (oldMethod != null && !oldMethod.equals(method)) {
			throw new IllegalStateException("Ambiguous @ExceptionHandler method mapped for [" +
					exceptionType + "]: {" + oldMethod + ", " + method + "}");
		}
	}

	private List<Class<? extends Throwable>> detectExceptionMappings(Method method) {
		List<Class<? extends Throwable>> result = new ArrayList<>();
		detectAnnotationExceptionMappings(method, result);
		if (result.isEmpty()) {
			for (Class<?> paramType : method.getParameterTypes()) {
				if (Throwable.class.isAssignableFrom(paramType)) {
					result.add((Class<? extends Throwable>) paramType);
				}
			}
		}
		if (result.isEmpty()) {
			throw new IllegalStateException("No exception types mapped to " + method);
		}
		return result;
	}

	private void detectAnnotationExceptionMappings(Method method, List<Class<? extends Throwable>> result) {
		ExceptionHandler ann = AnnotatedElementUtils.findMergedAnnotation(method, ExceptionHandler.class);
		Assert.state(ann != null, "No ExceptionHandler annotation");
		result.addAll(Arrays.asList(ann.value()));
	}

异常处理

DispatcherServlet#processDispatchResult，判断是否存在异常信息，存在异常信息，调用异常解析器。

	private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
			@Nullable Exception exception) throws Exception {

		boolean errorView = false;

		if (exception != null) {
			if (exception instanceof ModelAndViewDefiningException) {
				logger.debug("ModelAndViewDefiningException encountered", exception);
				mv = ((ModelAndViewDefiningException) exception).getModelAndView();
			}
			else {
				Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
				mv = processHandlerException(request, response, handler, exception);
				errorView = (mv != null);
			}
		}

		//...
	}

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

		// Success and error responses may use different content types
		request.removeAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);

		// Check registered HandlerExceptionResolvers...
		ModelAndView exMv = null;
		if (this.handlerExceptionResolvers != null) {
			for (HandlerExceptionResolver resolver : this.handlerExceptionResolvers) {
				exMv = resolver.resolveException(request, response, handler, ex);
				if (exMv != null) {
					break;
				}
			}
		}
        //...
    }

ExceptionHandlerExceptionResolver#doResolveHandlerMethodException，根据异常获取到处理方法，执行反射。

	@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();

		try {
			if (logger.isDebugEnabled()) {
				logger.debug("Using @ExceptionHandler " + exceptionHandlerMethod);
			}
			Throwable cause = exception.getCause();
			if (cause != null) {
				// Expose cause as provided argument as well
				exceptionHandlerMethod.invokeAndHandle(webRequest, mavContainer, exception, cause, handlerMethod);
			}
			else {
				// Otherwise, just the given exception as-is
				exceptionHandlerMethod.invokeAndHandle(webRequest, mavContainer, exception, handlerMethod);
			}
		}
		catch (Throwable invocationEx) {
			// Any other than the original exception (or its cause) is unintended here,
			// probably an accident (e.g. failed assertion or the like).
			if (invocationEx != exception && invocationEx != exception.getCause() && 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();
			HttpStatus 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) {
				Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes();
				RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
			}
			return mav;
		}
	}

ExceptionHandlerExceptionResolver#getExceptionHandlerMethod，创建异常解析器，根据异常解析方法。

	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.get(handlerType);
			if (resolver == null) {
				resolver = new ExceptionHandlerMethodResolver(handlerType);
				this.exceptionHandlerCache.put(handlerType, resolver);
			}
			Method method = resolver.resolveMethod(exception);
			if (method != null) {
				return new ServletInvocableHandlerMethod(handlerMethod.getBean(), method);
			}
			// 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);
				}
			}
		}

		return null;
	}

ExceptionHandlerMethodResolver#resolveMethod，获取异常的信息，从mappedMethods中获取对应的方法，按照ExceptionDepthComparator排序，获取优先级更高的匹配方法。

	@Nullable
	public Method resolveMethod(Exception exception) {
		return resolveMethodByThrowable(exception);
	}

	@Nullable
	public Method resolveMethodByThrowable(Throwable exception) {
		Method method = resolveMethodByExceptionType(exception.getClass());
		if (method == null) {
			Throwable cause = exception.getCause();
			if (cause != null) {
				method = resolveMethodByExceptionType(cause.getClass());
			}
		}
		return method;
	}

	@Nullable
	public Method resolveMethodByExceptionType(Class<? extends Throwable> exceptionType) {
		Method method = this.exceptionLookupCache.get(exceptionType);
		if (method == null) {
			method = getMappedMethod(exceptionType);
			this.exceptionLookupCache.put(exceptionType, method);
		}
		return method;
	}

	@Nullable
	private Method getMappedMethod(Class<? extends Throwable> exceptionType) {
		List<Class<? extends Throwable>> matches = new ArrayList<>();
		for (Class<? extends Throwable> mappedException : this.mappedMethods.keySet()) {
			if (mappedException.isAssignableFrom(exceptionType)) {
				matches.add(mappedException);
			}
		}
		if (!matches.isEmpty()) {
			matches.sort(new ExceptionDepthComparator(exceptionType));
			return this.mappedMethods.get(matches.get(0));
		}
		else {
			return null;
		}
	}

ServletInvocableHandlerMethod#invokeAndHandle，执行异常方法，得到响应结果。

	public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

		Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
		setResponseStatus(webRequest);

		if (returnValue == null) {
			if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
				disableContentCachingIfNecessary(webRequest);
				mavContainer.setRequestHandled(true);
				return;
			}
		}
		else if (StringUtils.hasText(getResponseStatusReason())) {
			mavContainer.setRequestHandled(true);
			return;
		}

		mavContainer.setRequestHandled(false);
		Assert.state(this.returnValueHandlers != null, "No return value handlers");
		try {
			this.returnValueHandlers.handleReturnValue(
					returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
		}
		catch (Exception ex) {
			if (logger.isTraceEnabled()) {
				logger.trace(formatErrorForReturnValue(returnValue), ex);
			}
			throw ex;
		}
	}

统一响应格式处理

demo展示

@ControllerAdvice(annotations = RestController.class)
public class ResultAdvice implements ResponseBodyAdvice<Object> {
    @Override
    public boolean supports(MethodParameter methodParameter,
                            Class<? extends HttpMessageConverter<?>> converterType) {

        //true 转换 false 不转换
        Class<?> parameterType = methodParameter.getParameterType();
        String returnTypeName = parameterType.getName();
        return !parameterType.isPrimitive() &&
                !returnTypeName.equals(String.class.getName()) &&
                !returnTypeName.equals(R.class.getName());
    }

    @Override
    public Object beforeBodyWrite(Object body,
                                  MethodParameter methodParameter,
                                  MediaType mediaType,
                                  Class<? extends HttpMessageConverter<?>> selectedConverterType,
                                  ServerHttpRequest request,
                                  ServerHttpResponse response) {
        return R.ok(body);
    }
}

原理解析

系统初始化

RequestMappingHandlerAdapter#afterPropertiesSet，系统启动会执行所有实现了InitializingBean的Bean的afterPropertiesSet方法。

	@Override
	public void afterPropertiesSet() {
		// Do this first, it may add ResponseBody advice beans
		initControllerAdviceCache();

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

RequestMappingHandlerAdapter#initControllerAdviceCache，获取容器中带有ControllerAdvice注解的Bean，封装成ControllerAdviceBean。如果是RequestBodyAdvice或者ResponseBodyAdvice，加入requestResponseBodyAdviceBeans。另外该方法还处理了ModelAttribute和InitBinder两个注解。

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

		List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());

		List<Object> requestResponseBodyAdviceBeans = new ArrayList<>();

		for (ControllerAdviceBean adviceBean : adviceBeans) {
			Class<?> beanType = adviceBean.getBeanType();
			if (beanType == null) {
				throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean);
			}
			Set<Method> attrMethods = MethodIntrospector.selectMethods(beanType, MODEL_ATTRIBUTE_METHODS);
			if (!attrMethods.isEmpty()) {
				this.modelAttributeAdviceCache.put(adviceBean, attrMethods);
			}
			Set<Method> binderMethods = MethodIntrospector.selectMethods(beanType, INIT_BINDER_METHODS);
			if (!binderMethods.isEmpty()) {
				this.initBinderAdviceCache.put(adviceBean, binderMethods);
			}
			if (RequestBodyAdvice.class.isAssignableFrom(beanType) || ResponseBodyAdvice.class.isAssignableFrom(beanType)) {
				requestResponseBodyAdviceBeans.add(adviceBean);
			}
		}

		if (!requestResponseBodyAdviceBeans.isEmpty()) {
			this.requestResponseBodyAdvice.addAll(0, requestResponseBodyAdviceBeans);
		}

		if (logger.isDebugEnabled()) {
			int modelSize = this.modelAttributeAdviceCache.size();
			int binderSize = this.initBinderAdviceCache.size();
			int reqCount = getBodyAdviceCount(RequestBodyAdvice.class);
			int resCount = getBodyAdviceCount(ResponseBodyAdvice.class);
			if (modelSize == 0 && binderSize == 0 && reqCount == 0 && resCount == 0) {
				logger.debug("ControllerAdvice beans: none");
			}
			else {
				logger.debug("ControllerAdvice beans: " + modelSize + " @ModelAttribute, " + binderSize +
						" @InitBinder, " + reqCount + " RequestBodyAdvice, " + resCount + " ResponseBodyAdvice");
			}
		}
	}

RequestMappingHandlerAdapter#getDefaultArgumentResolvers，加载解析器，会将requestResponseBodyAdvice加载到RequestResponseBodyMethodProcessor

	private List<HandlerMethodArgumentResolver> getDefaultArgumentResolvers() {
		List<HandlerMethodArgumentResolver> resolvers = new ArrayList<>(30);

		// Annotation-based argument resolution
		//...
		resolvers.add(new RequestResponseBodyMethodProcessor(getMessageConverters(), this.requestResponseBodyAdvice));
		resolvers.add(new RequestPartMethodArgumentResolver(getMessageConverters(), this.requestResponseBodyAdvice));
		//...

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

		// Catch-all
		resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));
		resolvers.add(new ServletModelAttributeMethodProcessor(true));

		return resolvers;
	}

RequestResponseBodyMethodProcessor继承了AbstractMessageConverterMethodArgumentResolver，构造函数中初始化RequestResponseBodyAdviceChain。

	public AbstractMessageConverterMethodArgumentResolver(List<HttpMessageConverter<?>> converters,
			@Nullable List<Object> requestResponseBodyAdvice) {

		Assert.notEmpty(converters, "'messageConverters' must not be empty");
		this.messageConverters = converters;
		this.allSupportedMediaTypes = getAllSupportedMediaTypes(converters);
		this.advice = new RequestResponseBodyAdviceChain(requestResponseBodyAdvice);
	}

RequestResponseBodyAdviceChain主要是处理了RequestBodyAdvice和ResponseBodyAdvice。

	public RequestResponseBodyAdviceChain(@Nullable List<Object> requestResponseBodyAdvice) {
		this.requestBodyAdvice.addAll(getAdviceByType(requestResponseBodyAdvice, RequestBodyAdvice.class));
		this.responseBodyAdvice.addAll(getAdviceByType(requestResponseBodyAdvice, ResponseBodyAdvice.class));
	}

	@SuppressWarnings("unchecked")
	static <T> List<T> getAdviceByType(@Nullable List<Object> requestResponseBodyAdvice, Class<T> adviceType) {
		if (requestResponseBodyAdvice != null) {
			List<T> result = new ArrayList<>();
			for (Object advice : requestResponseBodyAdvice) {
				Class<?> beanType = (advice instanceof ControllerAdviceBean ?
						((ControllerAdviceBean) advice).getBeanType() : advice.getClass());
				if (beanType != null && adviceType.isAssignableFrom(beanType)) {
					result.add((T) advice);
				}
			}
			return result;
		}
		return Collections.emptyList();
	}

响应处理

RequestResponseBodyMethodProcessor#handleReturnValue。返回的响应有@ResponseBody注解，响应处理器就是RequestResponseBodyMethodProcessor

	@Override
	public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest)
			throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {

		mavContainer.setRequestHandled(true);
		ServletServerHttpRequest inputMessage = createInputMessage(webRequest);
		ServletServerHttpResponse outputMessage = createOutputMessage(webRequest);

		// Try even with null return value. ResponseBodyAdvice could get involved.
		writeWithMessageConverters(returnValue, returnType, inputMessage, outputMessage);
	}

AbstractMessageConverterMethodProcessor#writeWithMessageConverters，会调用getAdvice().beforeBodyWrite。

	protected <T> void writeWithMessageConverters(@Nullable T value, MethodParameter returnType,
			ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage)
			throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {

		Object body;
		Class<?> valueType;
		Type targetType;
		//...

		if (selectedMediaType != null) {
			selectedMediaType = selectedMediaType.removeQualityValue();
			for (HttpMessageConverter<?> converter : this.messageConverters) {
				GenericHttpMessageConverter genericConverter = (converter instanceof GenericHttpMessageConverter ?
						(GenericHttpMessageConverter<?>) converter : null);
				if (genericConverter != null ?
						((GenericHttpMessageConverter) converter).canWrite(targetType, valueType, selectedMediaType) :
						converter.canWrite(valueType, selectedMediaType)) {
					body = getAdvice().beforeBodyWrite(body, returnType, selectedMediaType,
							(Class<? extends HttpMessageConverter<?>>) converter.getClass(),
							inputMessage, outputMessage);
					if (body != null) {
						Object theBody = body;
						LogFormatUtils.traceDebug(logger, traceOn ->
								"Writing [" + LogFormatUtils.formatValue(theBody, !traceOn) + "]");
						addContentDispositionHeader(inputMessage, outputMessage);
						if (genericConverter != null) {
							genericConverter.write(body, targetType, selectedMediaType, outputMessage);
						}
						else {
							((HttpMessageConverter) converter).write(body, selectedMediaType, outputMessage);
						}
					}
					else {
						if (logger.isDebugEnabled()) {
							logger.debug("Nothing to write: null body");
						}
					}
					return;
				}
			}
		}

		if (body != null) {
			Set<MediaType> producibleMediaTypes =
					(Set<MediaType>) inputMessage.getServletRequest()
							.getAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);

			if (isContentTypePreset || !CollectionUtils.isEmpty(producibleMediaTypes)) {
				throw new HttpMessageNotWritableException(
						"No converter for [" + valueType + "] with preset Content-Type '" + contentType + "'");
			}
			throw new HttpMediaTypeNotAcceptableException(this.allSupportedMediaTypes);
		}
	}

RequestResponseBodyAdviceChain#beforeBodyWrite，获取匹配的ResponseBodyAdvice，判断类型是否支持，进行处理。

	@Override
	@Nullable
	public Object beforeBodyWrite(@Nullable Object body, MethodParameter returnType, MediaType contentType,
			Class<? extends HttpMessageConverter<?>> converterType,
			ServerHttpRequest request, ServerHttpResponse response) {

		return processBody(body, returnType, contentType, converterType, request, response);
	}

	@Nullable
	private <T> Object processBody(@Nullable Object body, MethodParameter returnType, MediaType contentType,
			Class<? extends HttpMessageConverter<?>> converterType,
			ServerHttpRequest request, ServerHttpResponse response) {

		for (ResponseBodyAdvice<?> advice : getMatchingAdvice(returnType, ResponseBodyAdvice.class)) {
			if (advice.supports(returnType, converterType)) {
				body = ((ResponseBodyAdvice<T>) advice).beforeBodyWrite((T) body, returnType,
						contentType, converterType, request, response);
			}
		}
		return body;
	}

RequestResponseBodyAdviceChain#getMatchingAdvice，如果类型是RequestBodyAdvice或者ResponseBodyAdvice，从对应的属性上获取数据。如果是ControllerAdviceBean，执行resolveBean方法。

	@SuppressWarnings("unchecked")
	private <A> List<A> getMatchingAdvice(MethodParameter parameter, Class<? extends A> adviceType) {
		List<Object> availableAdvice = getAdvice(adviceType);
		if (CollectionUtils.isEmpty(availableAdvice)) {
			return Collections.emptyList();
		}
		List<A> result = new ArrayList<>(availableAdvice.size());
		for (Object advice : availableAdvice) {
			if (advice instanceof ControllerAdviceBean) {
				ControllerAdviceBean adviceBean = (ControllerAdviceBean) advice;
				if (!adviceBean.isApplicableToBeanType(parameter.getContainingClass())) {
					continue;
				}
				advice = adviceBean.resolveBean();
			}
			if (adviceType.isAssignableFrom(advice.getClass())) {
				result.add((A) advice);
			}
		}
		return result;
	}

	private List<Object> getAdvice(Class<?> adviceType) {
		if (RequestBodyAdvice.class == adviceType) {
			return this.requestBodyAdvice;
		}
		else if (ResponseBodyAdvice.class == adviceType) {
			return this.responseBodyAdvice;
		}
		else {
			throw new IllegalArgumentException("Unexpected adviceType: " + adviceType);
		}
	}

ControllerAdviceBean#resolveBean，获取用spring管理的对应的实体类。

    public Object resolveBean() {
        if (this.resolvedBean == null) {
            Object resolvedBean = this.obtainBeanFactory().getBean((String)this.beanOrName);
            if (!this.isSingleton) {
                return resolvedBean;
            }

            this.resolvedBean = resolvedBean;
        }

        return this.resolvedBean;
    }

同理，RequestBodyAdvice在接收参数的时候，也在做对应的处理。AbstractMessageConverterMethodArgumentResolver#readWithMessageConverters()。该方法会执行getAdvice().beforeBodyRead和getAdvice().afterBodyRead。

	protected <T> Object readWithMessageConverters(HttpInputMessage inputMessage, MethodParameter parameter,
			Type targetType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {

		//...

		HttpMethod httpMethod = (inputMessage instanceof HttpRequest ? ((HttpRequest) inputMessage).getMethod() : null);
		Object body = NO_VALUE;

		EmptyBodyCheckingHttpInputMessage message;
		try {
			message = new EmptyBodyCheckingHttpInputMessage(inputMessage);

			for (HttpMessageConverter<?> converter : this.messageConverters) {
				Class<HttpMessageConverter<?>> converterType = (Class<HttpMessageConverter<?>>) converter.getClass();
				GenericHttpMessageConverter<?> genericConverter =
						(converter instanceof GenericHttpMessageConverter ? (GenericHttpMessageConverter<?>) converter : null);
				if (genericConverter != null ? genericConverter.canRead(targetType, contextClass, contentType) :
						(targetClass != null && converter.canRead(targetClass, contentType))) {
					if (message.hasBody()) {
						HttpInputMessage msgToUse =
								getAdvice().beforeBodyRead(message, parameter, targetType, converterType);
						body = (genericConverter != null ? genericConverter.read(targetType, contextClass, msgToUse) :
								((HttpMessageConverter<T>) converter).read(targetClass, msgToUse));
						body = getAdvice().afterBodyRead(body, msgToUse, parameter, targetType, converterType);
					}
					else {
						body = getAdvice().handleEmptyBody(null, message, parameter, targetType, converterType);
					}
					break;
				}
			}
		}
		catch (IOException ex) {
			throw new HttpMessageNotReadableException("I/O error while reading input message", ex, inputMessage);
		}

		//...

		return body;
	}

RequestResponseBodyAdviceChain#beforeBodyRead

	@Override
	public HttpInputMessage beforeBodyRead(HttpInputMessage request, MethodParameter parameter,
			Type targetType, Class<? extends HttpMessageConverter<?>> converterType) throws IOException {

		for (RequestBodyAdvice advice : getMatchingAdvice(parameter, RequestBodyAdvice.class)) {
			if (advice.supports(parameter, targetType, converterType)) {
				request = advice.beforeBodyRead(request, parameter, targetType, converterType);
			}
		}
		return request;
	}

	@Override
	public Object afterBodyRead(Object body, HttpInputMessage inputMessage, MethodParameter parameter,
			Type targetType, Class<? extends HttpMessageConverter<?>> converterType) {

		for (RequestBodyAdvice advice : getMatchingAdvice(parameter, RequestBodyAdvice.class)) {
			if (advice.supports(parameter, targetType, converterType)) {
				body = advice.afterBodyRead(body, inputMessage, parameter, targetType, converterType);
			}
		}
		return body;
	}