Spring MVC ControllerAdvice深入解析

作者: 良辰美景TT | 来源:发表于2018-08-10 11:51 被阅读10次

Spring 在3.2版本后面增加了一个ControllerAdvice注解。网上的资料说的都是ControllerAdvice配合ExceptionHandler注解可以统一处理异常。而Spring MVC是如何做到的资料却比较少，下面会先给出使用的例子和踩过的一个坑。然后进行相应的源码分析，之后再介始ControllerAdvice另外的两种使用方式。

ControllerAdvice的简单使用

ControllerAdvice配合ExceptionHandler可以统一处理系统的异常，我们先定义一个ExceptionAdvice类用于处理系统的两种类型的异常。代码如下：

import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;

import com.pptv.frame.dto.common.ResponseDTO;
import com.pptv.frame.dto.common.ServiceCodeEnum;

@ControllerAdvice
public class ExceptionAdvice {

    @ExceptionHandler({
                        ArrayIndexOutOfBoundsException.class
    })
    @ResponseBody
    public ResponseDTO handleArrayIndexOutOfBoundsException(ArrayIndexOutOfBoundsException e) {
        // TODO 记录log日志
        e.printStackTrace();
        ResponseDTO responseDTO = new ResponseDTO();
        responseDTO.wrapResponse(ServiceCodeEnum.E999998, "数组越界异常");

        return responseDTO;
    }

    @ExceptionHandler({
                        Exception.class
    })
    @ResponseBody
    public ResponseDTO handleException(Exception e) {
        // TODO 记录log日志
        e.printStackTrace();
        ResponseDTO responseDTO = new ResponseDTO();
        responseDTO.wrapResponse(ServiceCodeEnum.E999998, "未知异常");
        return responseDTO;
    }

}

Spring mvc 的配置如下(这里用到了mvc:annotation-driven)：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:cxf="http://cxf.apache.org/core"
    xmlns:p="http://cxf.apache.org/policy" xmlns:ss="http://www.springframework.org/schema/security"
    xmlns:jaxws="http://cxf.apache.org/jaxws" xmlns:jee="http://www.springframework.org/schema/jee"
    xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd 
    http://cxf.apache.org/core http://cxf.apache.org/schemas/core.xsd 
    http://cxf.apache.org/jaxws http://cxf.apache.org/schemas/jaxws.xsd 
    http://cxf.apache.org/policy http://cxf.apache.org/schemas/policy.xsd
    http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd
    http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee.xsd
    http://cxf.apache.org/bindings/soap http://cxf.apache.org/schemas/configuration/soap.xsd 
    http://www.springframework.org/schema/security http://www.springframework.org/schema/security/spring-security.xsd 
    http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd
    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
    http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd">

    <context:component-scan
        base-package="frame.web.controller;frame.web.advice" />

    <!--===================== view resovler ===================== -->
    <bean id="jstlViewResolver"
        class="org.springframework.web.servlet.view.UrlBasedViewResolver">
        <property name="order" value="1" />
        <property name="viewClass"
            value="org.springframework.web.servlet.view.JstlView" />
        <property name="prefix" value="/WEB-INF/jsp/" />
    </bean>

    <!-- 配置Fastjson支持 -->
    <mvc:annotation-driven conversion-service="conversionService">
        <mvc:message-converters register-defaults="true">
            <bean
                class="com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter">
                <property name="supportedMediaTypes" value="text/html;charset=UTF-8" />
                <property name="features">
                    <array>
                        <value>WriteMapNullValue</value>
                        <value>WriteNullStringAsEmpty</value>
                    </array>
                </property>
            </bean>
        </mvc:message-converters>
    </mvc:annotation-driven>

    <!-- 自定义参数转换 -->
    <bean id="conversionService"
        class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
    </bean>

</beans>

遇到的一个坑是当spring mvc配置文件不用<mvc:annotation-drive>这个标签而是手动将RequestMappingHandlerMapping与RequestMappingHandlerAdapter这两个类让spring容器管理，上面的ControllerAdvice将不起作用

    <bean
        class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping" />
    <bean
        class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
        <property name="webBindingInitializer">
            <bean
                class="org.springframework.web.bind.support.ConfigurableWebBindingInitializer">
                <property name="conversionService" ref="conversionService" />
            </bean>
        </property>
        <property name="messageConverters">
            <list>
                <ref bean="mappingJackson2HttpMessageConverter" />
                <ref bean="stringHttpMessageConverter" />
            </list>
        </property>
    </bean>

Spring MVC是如何处理异常的

下面来看看Spring MVC是如何处理异常的，为什么我手动配置了RequestMappingHandlerMapping和RequestMappingHandlerAdapter ControllerAdvice就不会对异常进行拦截呢而通过<mvc:annotation-drive>这个标签就可以呢？我们从Spring MVC的入口看一下异常是如何处理的。下面是关键代码（关键代码都有相应的注释）：

public class DispatcherServlet extends FrameworkServlet {
/**
  *这个方法是Spring MVC的入口方法，可以看到Spring MVC人具体处理流程
 **/
    protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpServletRequest processedRequest = request;
        HandlerExecutionChain mappedHandler = null;
        boolean multipartRequestParsed = false;

        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

        try {
            ModelAndView mv = null;
            Exception dispatchException = null;
//这里有个try，下面的catch就是用于处理异常的
            try {
                              //检查是否是上传文件的请求
                processedRequest = checkMultipart(request);
                multipartRequestParsed = (processedRequest != request);

                // Determine handler for the current request.
//根据请求的request得到HandlerExecutionChain 对象，里面有Inceptor和相应的Controller
                mappedHandler = getHandler(processedRequest);
                if (mappedHandler == null || mappedHandler.getHandler() == null) {
                    noHandlerFound(processedRequest, response);
                    return;
                }

                // Determine handler adapter for the current request.
//根据配置的HandlerAdapter 对handler进行适配
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

                // Process last-modified header, if supported by the handler.
                String method = request.getMethod();
                boolean isGet = "GET".equals(method);
                if (isGet || "HEAD".equals(method)) {
                    long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                    if (logger.isDebugEnabled()) {
                        logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
                    }
                    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                        return;
                    }
                }

                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }

                // Actually invoke the handler. 
//这里会调用具体的Handler也就是我们写的Controller
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }

                applyDefaultViewName(processedRequest, mv);
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }
            catch (Exception ex) {
//上面处理的逻辑有任何的异常，都将会落到这里，用dispatchException 这个变量接住异常引用
                dispatchException = ex;
            }
            catch (Throwable err) {
//如果抛的是error， 这里也会把异常给接住 
                // As of 4.3, we're processing Errors thrown from handler methods as well,
                // making them available for @ExceptionHandler methods and other scenarios.
                dispatchException = new NestedServletException("Handler dispatch failed", err);
            }
//具体处理异常的逻辑看来是在这个方法里了，具体的逻辑看下面的源码
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        }
        catch (Exception ex) {
//这是最外面的try，这里需要处理Inteceptor里After的逻辑
            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
        }
        catch (Throwable err) {
//这是最外面的try，这里需要处理Inteceptor里After的逻辑
            triggerAfterCompletion(processedRequest, response, mappedHandler,
                    new NestedServletException("Handler processing failed", err));
        }
        finally {
            if (asyncManager.isConcurrentHandlingStarted()) {
                // Instead of postHandle and afterCompletion
                if (mappedHandler != null) {
                    mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
                }
            }
            else {
                // Clean up any resources used by a multipart request.
                if (multipartRequestParsed) {
                    cleanupMultipart(processedRequest);
                }
            }
        }
    }

/**
*这个方法里processHandlerException用于处理各种不同的Exception
**/
    private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
            HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {

        boolean errorView = false;
//当controller抛出异常后，就会执行下面的逻辑啦
        if (exception != null) {
            if (exception instanceof ModelAndViewDefiningException) {
                logger.debug("ModelAndViewDefiningException encountered", exception);
                mv = ((ModelAndViewDefiningException) exception).getModelAndView();
            }
            else {
//各种不同的异常会走到这里来处理，processHandlerException的源码在下面有详细的注释
                Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
                mv = processHandlerException(request, response, handler, exception);
                errorView = (mv != null);
            }
        }

        // Did the handler return a view to render?
        if (mv != null && !mv.wasCleared()) {
            render(mv, request, response);
            if (errorView) {
                WebUtils.clearErrorRequestAttributes(request);
            }
        }
        else {
            if (logger.isDebugEnabled()) {
                logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
                        "': assuming HandlerAdapter completed request handling");
            }
        }

        if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
            // Concurrent handling started during a forward
            return;
        }

        if (mappedHandler != null) {
            mappedHandler.triggerAfterCompletion(request, response, null);
        }
    }

/**
**这里是用于处理Spring MVC异常的入口
**/
    protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
            Object handler, Exception ex) throws Exception {

        // Check registered HandlerExceptionResolvers...
//通过注入的handlerExceptionResolvers来处得具体的Exception，这也就找到了我上面踩坑的原因了。
        ModelAndView exMv = null;
        for (HandlerExceptionResolver handlerExceptionResolver : this.handlerExceptionResolvers) {
            exMv = handlerExceptionResolver.resolveException(request, response, handler, ex);
            if (exMv != null) {
                break;
            }
        }
        if (exMv != null) {
            if (exMv.isEmpty()) {
                request.setAttribute(EXCEPTION_ATTRIBUTE, ex);
                return null;
            }
            // We might still need view name translation for a plain error model...
            if (!exMv.hasView()) {
                exMv.setViewName(getDefaultViewName(request));
            }
            if (logger.isDebugEnabled()) {
                logger.debug("Handler execution resulted in exception - forwarding to resolved error view: " + exMv, ex);
            }
            WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());
            return exMv;
        }

        throw ex;
    }

}

通过上面的源码，我们一步步可以跟踪到processHandlerException这个方法，这个方法里通过HandlerExceptionResolver 来处理具体的异常，而当我们手动只配置RequestMappingHandlerMapping和RequestMappingHandlerAdapter时，并没有配置任何的HandlerExceptionResolver 。也就是为什么ControllerAdvice不会对异常进行处理了，我们同时也可以想到<mvc:annotation-drive>一定是帮助我们注入了一个HandlerExceptionResolver 类。下面我们通过分析AnnotationDrivenBeanDefinitionParser这个类来看看到底给我们注入的是那个HandlerExceptionResolver，AnnotationDrivenBeanDefinitionParser类就是用于解析<mvc:annotation-drive>标签的。下面是AnnotationDrivenBeanDefinitionParser的部分源码：

package org.springframework.web.servlet.config;

class AnnotationDrivenBeanDefinitionParser implements BeanDefinitionParser {

/**
*parse是这个类的核心方法，它用于解析 annotation-drive标签里的内容，根据标签里的内容往spring ioc容器里注入具体的对象。
**/
    @Override
    public BeanDefinition parse(Element element, ParserContext parserContext) {
        Object source = parserContext.extractSource(element);
        XmlReaderContext readerContext = parserContext.getReaderContext();

        CompositeComponentDefinition compDefinition = new CompositeComponentDefinition(element.getTagName(), source);
        parserContext.pushContainingComponent(compDefinition);

        RuntimeBeanReference contentNegotiationManager = getContentNegotiationManager(element, source, parserContext);
//这里有我们熟悉的RequestMappingHandlerMapping，
        RootBeanDefinition handlerMappingDef = new RootBeanDefinition(RequestMappingHandlerMapping.class);
        handlerMappingDef.setSource(source);
        handlerMappingDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        handlerMappingDef.getPropertyValues().add("order", 0);
        handlerMappingDef.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);

        if (element.hasAttribute("enable-matrix-variables")) {
            Boolean enableMatrixVariables = Boolean.valueOf(element.getAttribute("enable-matrix-variables"));
            handlerMappingDef.getPropertyValues().add("removeSemicolonContent", !enableMatrixVariables);
        }
        else if (element.hasAttribute("enableMatrixVariables")) {
            Boolean enableMatrixVariables = Boolean.valueOf(element.getAttribute("enableMatrixVariables"));
            handlerMappingDef.getPropertyValues().add("removeSemicolonContent", !enableMatrixVariables);
        }

        configurePathMatchingProperties(handlerMappingDef, element, parserContext);
        readerContext.getRegistry().registerBeanDefinition(HANDLER_MAPPING_BEAN_NAME , handlerMappingDef);

        RuntimeBeanReference corsConfigurationsRef = MvcNamespaceUtils.registerCorsConfigurations(null, parserContext, source);
        handlerMappingDef.getPropertyValues().add("corsConfigurations", corsConfigurationsRef);

//这里会注入具体的ConversionService用于将json,xml转成Spring mvc里的请求和返回对象
        RuntimeBeanReference conversionService = getConversionService(element, source, parserContext);

        RuntimeBeanReference validator = getValidator(element, source, parserContext);
        RuntimeBeanReference messageCodesResolver = getMessageCodesResolver(element);

        RootBeanDefinition bindingDef = new RootBeanDefinition(ConfigurableWebBindingInitializer.class);
        bindingDef.setSource(source);
        bindingDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        bindingDef.getPropertyValues().add("conversionService", conversionService);
        bindingDef.getPropertyValues().add("validator", validator);
        bindingDef.getPropertyValues().add("messageCodesResolver", messageCodesResolver);

        ManagedList<?> messageConverters = getMessageConverters(element, source, parserContext);
        ManagedList<?> argumentResolvers = getArgumentResolvers(element, parserContext);
        ManagedList<?> returnValueHandlers = getReturnValueHandlers(element, parserContext);
        String asyncTimeout = getAsyncTimeout(element);
        RuntimeBeanReference asyncExecutor = getAsyncExecutor(element);
        ManagedList<?> callableInterceptors = getCallableInterceptors(element, source, parserContext);
        ManagedList<?> deferredResultInterceptors = getDeferredResultInterceptors(element, source, parserContext);
//RequestMappingHandlerAdapter也会在这里注入
        RootBeanDefinition handlerAdapterDef = new RootBeanDefinition(RequestMappingHandlerAdapter.class);
        handlerAdapterDef.setSource(source);
        handlerAdapterDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        handlerAdapterDef.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);
        handlerAdapterDef.getPropertyValues().add("webBindingInitializer", bindingDef);
        handlerAdapterDef.getPropertyValues().add("messageConverters", messageConverters);
        addRequestBodyAdvice(handlerAdapterDef);
        addResponseBodyAdvice(handlerAdapterDef);

        if (element.hasAttribute("ignore-default-model-on-redirect")) {
            Boolean ignoreDefaultModel = Boolean.valueOf(element.getAttribute("ignore-default-model-on-redirect"));
            handlerAdapterDef.getPropertyValues().add("ignoreDefaultModelOnRedirect", ignoreDefaultModel);
        }
        else if (element.hasAttribute("ignoreDefaultModelOnRedirect")) {
            // "ignoreDefaultModelOnRedirect" spelling is deprecated
            Boolean ignoreDefaultModel = Boolean.valueOf(element.getAttribute("ignoreDefaultModelOnRedirect"));
            handlerAdapterDef.getPropertyValues().add("ignoreDefaultModelOnRedirect", ignoreDefaultModel);
        }

        if (argumentResolvers != null) {
            handlerAdapterDef.getPropertyValues().add("customArgumentResolvers", argumentResolvers);
        }
        if (returnValueHandlers != null) {
            handlerAdapterDef.getPropertyValues().add("customReturnValueHandlers", returnValueHandlers);
        }
        if (asyncTimeout != null) {
            handlerAdapterDef.getPropertyValues().add("asyncRequestTimeout", asyncTimeout);
        }
        if (asyncExecutor != null) {
            handlerAdapterDef.getPropertyValues().add("taskExecutor", asyncExecutor);
        }

        handlerAdapterDef.getPropertyValues().add("callableInterceptors", callableInterceptors);
        handlerAdapterDef.getPropertyValues().add("deferredResultInterceptors", deferredResultInterceptors);
        readerContext.getRegistry().registerBeanDefinition(HANDLER_ADAPTER_BEAN_NAME , handlerAdapterDef);

        String uriCompContribName = MvcUriComponentsBuilder.MVC_URI_COMPONENTS_CONTRIBUTOR_BEAN_NAME;
        RootBeanDefinition uriCompContribDef = new RootBeanDefinition(CompositeUriComponentsContributorFactoryBean.class);
        uriCompContribDef.setSource(source);
        uriCompContribDef.getPropertyValues().addPropertyValue("handlerAdapter", handlerAdapterDef);
        uriCompContribDef.getPropertyValues().addPropertyValue("conversionService", conversionService);
        readerContext.getRegistry().registerBeanDefinition(uriCompContribName, uriCompContribDef);

        RootBeanDefinition csInterceptorDef = new RootBeanDefinition(ConversionServiceExposingInterceptor.class);
        csInterceptorDef.setSource(source);
        csInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(0, conversionService);
        RootBeanDefinition mappedCsInterceptorDef = new RootBeanDefinition(MappedInterceptor.class);
        mappedCsInterceptorDef.setSource(source);
        mappedCsInterceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        mappedCsInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(0, (Object) null);
        mappedCsInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(1, csInterceptorDef);
        String mappedInterceptorName = readerContext.registerWithGeneratedName(mappedCsInterceptorDef);

//这里有我们需要找的ExceptionHandlerExceptionResolver，
        RootBeanDefinition exceptionHandlerExceptionResolver = new RootBeanDefinition(ExceptionHandlerExceptionResolver.class);
        exceptionHandlerExceptionResolver.setSource(source);
        exceptionHandlerExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        exceptionHandlerExceptionResolver.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);
        exceptionHandlerExceptionResolver.getPropertyValues().add("messageConverters", messageConverters);
        exceptionHandlerExceptionResolver.getPropertyValues().add("order", 0);
        addResponseBodyAdvice(exceptionHandlerExceptionResolver);

        if (argumentResolvers != null) {
            exceptionHandlerExceptionResolver.getPropertyValues().add("customArgumentResolvers", argumentResolvers);
        }
        if (returnValueHandlers != null) {
            exceptionHandlerExceptionResolver.getPropertyValues().add("customReturnValueHandlers", returnValueHandlers);
        }

        String methodExceptionResolverName = readerContext.registerWithGeneratedName(exceptionHandlerExceptionResolver);

        RootBeanDefinition responseStatusExceptionResolver = new RootBeanDefinition(ResponseStatusExceptionResolver.class);
        responseStatusExceptionResolver.setSource(source);
        responseStatusExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        responseStatusExceptionResolver.getPropertyValues().add("order", 1);
        String responseStatusExceptionResolverName =
                readerContext.registerWithGeneratedName(responseStatusExceptionResolver);

        RootBeanDefinition defaultExceptionResolver = new RootBeanDefinition(DefaultHandlerExceptionResolver.class);
        defaultExceptionResolver.setSource(source);
        defaultExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        defaultExceptionResolver.getPropertyValues().add("order", 2);
        String defaultExceptionResolverName =
                readerContext.registerWithGeneratedName(defaultExceptionResolver);

        parserContext.registerComponent(new BeanComponentDefinition(handlerMappingDef, HANDLER_MAPPING_BEAN_NAME));
        parserContext.registerComponent(new BeanComponentDefinition(handlerAdapterDef, HANDLER_ADAPTER_BEAN_NAME));
        parserContext.registerComponent(new BeanComponentDefinition(uriCompContribDef, uriCompContribName));
        parserContext.registerComponent(new BeanComponentDefinition(exceptionHandlerExceptionResolver, methodExceptionResolverName));
        parserContext.registerComponent(new BeanComponentDefinition(responseStatusExceptionResolver, responseStatusExceptionResolverName));
        parserContext.registerComponent(new BeanComponentDefinition(defaultExceptionResolver, defaultExceptionResolverName));
        parserContext.registerComponent(new BeanComponentDefinition(mappedCsInterceptorDef, mappedInterceptorName));

        // Ensure BeanNameUrlHandlerMapping (SPR-8289) and default HandlerAdapters are not "turned off"
        MvcNamespaceUtils.registerDefaultComponents(parserContext, source);

        parserContext.popAndRegisterContainingComponent();

        return null;
    }
}

通过上面代码的分析，我们可以找到ExceptionHandlerExceptionResolver这个类来用于处理Spring MVC的各种异常，那ExceptionHandlerExceptionResolver具体又是如何跟ControllerAdvice配合使用来处理各种异常的呢?我们来看看ExceptionHandlerExceptionResolver里的关键代码：

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

public class ExceptionHandlerExceptionResolver extends AbstractHandlerMethodExceptionResolver
        implements ApplicationContextAware, InitializingBean {
//这里有个map用于保存ControllerAdviceBean
    private final Map<ControllerAdviceBean, ExceptionHandlerMethodResolver> exceptionHandlerAdviceCache =
            new LinkedHashMap<ControllerAdviceBean, ExceptionHandlerMethodResolver>();

//这个方法是由spring 容器调用的
    @Override
    public void afterPropertiesSet() {
        // Do this first, it may add ResponseBodyAdvice beans
//这个方法里会处理ExceptionHandler
        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);
        }
    }

/**
*这个方法里会在spring ioc容器里找出标注了@ControllerAdvice的类，如果有方法标注了@ExceptionHandler会生成一个ExceptionHandlerMethodResolver类用于处理异常并放到exceptionHandlerAdviceCache这个map缓存类里。
**/
    private void initExceptionHandlerAdviceCache() {
        if (getApplicationContext() == null) {
            return;
        }
        if (logger.isDebugEnabled()) {
            logger.debug("Looking for exception mappings: " + getApplicationContext());
        }
//这里会找到容器里标注了ControllerAdvice标签的类
        List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
        AnnotationAwareOrderComparator.sort(adviceBeans);

        for (ControllerAdviceBean adviceBean : adviceBeans) {
//这个构造方法里会检查ControllerAdvice类里是否有@ExceptionHandler标注的方法，在ExceptionHandlerMethodResolver 有个异常的map。
            ExceptionHandlerMethodResolver resolver = new ExceptionHandlerMethodResolver(adviceBean.getBeanType());
            if (resolver.hasExceptionMappings()) {
//如果有@ExceptionHandler方法，会执行下面的逻辑
                this.exceptionHandlerAdviceCache.put(adviceBean, resolver);
                if (logger.isInfoEnabled()) {
                    logger.info("Detected @ExceptionHandler methods in " + adviceBean);
                }
            }
            if (ResponseBodyAdvice.class.isAssignableFrom(adviceBean.getBeanType())) {
                this.responseBodyAdvice.add(adviceBean);
                if (logger.isInfoEnabled()) {
                    logger.info("Detected ResponseBodyAdvice implementation in " + adviceBean);
                }
            }
        }
    }

/**
** 这个方法会根据exceptionHandlerAdviceCache这个找到具体需要处理异常的方法
*/
    protected ServletInvocableHandlerMethod getExceptionHandlerMethod(HandlerMethod handlerMethod, Exception exception) {
        Class<?> handlerType = (handlerMethod != null ? handlerMethod.getBeanType() : null);

        if (handlerMethod != null) {
            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 (Entry<ControllerAdviceBean, ExceptionHandlerMethodResolver> entry : this.exceptionHandlerAdviceCache.entrySet()) {
            if (entry.getKey().isApplicableToBeanType(handlerType)) {
                ExceptionHandlerMethodResolver resolver = entry.getValue();
//根据具体的异常找到处理异常的方法，然后调用
                Method method = resolver.resolveMethod(exception);
                if (method != null) {
                    return new ServletInvocableHandlerMethod(entry.getKey().resolveBean(), method);
                }
            }
        }

        return null;
    }
}

ExceptionHandlerExceptionResolver这个类首先会扫描容器里所有的ControllerAdvice,如果ControllerAdvice标注了@ExceptionHandler会加到一个map缓存里。在处理具体的异常的时候，会去这个缓存里一个个找是否有ControllerAdvice能够处理这个异常。整个流程我们就分析到这里，下面看看ControllerAdvice的另外两个用法。

RequestBodyAdvice与ResponseBodyAdvice

Spring在4.2的版本给我们提供了RequestBodyAdvice与ResponseBodyAdvice这两个接口，而ControllerAdvice是在3.2这个版本里的。那RequestBodyAdvice和ResponseBodyAdvice能够帮我们做些什么事性呢？假如现在有个需求，正常接口返回的是json，但传入的请求头里有callback参数需要返回jsonp格式的数据需要如何做呢？下面我们来看看RequestBodyAdvice和ResponseBodyAdvice这两个类的具体定义，RequestBodyAdvice代码如下：

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

import java.io.IOException;
import java.lang.reflect.Type;

import org.springframework.core.MethodParameter;
import org.springframework.http.HttpInputMessage;
import org.springframework.http.converter.HttpMessageConverter;

public interface RequestBodyAdvice {
//supports方法用于决定是否调用下面的方法，
    boolean supports(MethodParameter methodParameter, Type targetType,
            Class<? extends HttpMessageConverter<?>> converterType);

//处理空参数据情况
    Object handleEmptyBody(Object body, HttpInputMessage inputMessage, MethodParameter parameter,
            Type targetType, Class<? extends HttpMessageConverter<?>> converterType);

//在参数读取之前处理的逻辑
    HttpInputMessage beforeBodyRead(HttpInputMessage inputMessage, MethodParameter parameter,
            Type targetType, Class<? extends HttpMessageConverter<?>> converterType) throws IOException;

//在参数读取之后处理的逻辑
    Object afterBodyRead(Object body, HttpInputMessage inputMessage, MethodParameter parameter,
            Type targetType, Class<? extends HttpMessageConverter<?>> converterType);

}

从RequestBodyAdvice的定义我们可以清楚的看出他主要用于处理Spring MVC请求参数相关的逻辑，首先定义了support方法用于判断是否能够对请求参数做进一步的处理，然后定义了在读取参数前后方法分别用于处理请求参数。这里的读取前后是在Spring MVC调用了HttpMessageConverter对参数进行了转义，所以使用起来还是很方便的。下面来看看ResponseBodyAdvice的定义：

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

import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;

public interface ResponseBodyAdvice<T> {

//这个方法用于判断是否需要调用beforeBodyWrite方法
    boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType);

//这里在写入的时候就可以修改要写入的值啦
    T beforeBodyWrite(T body, MethodParameter returnType, MediaType selectedContentType,
            Class<? extends HttpMessageConverter<?>> selectedConverterType,
            ServerHttpRequest request, ServerHttpResponse response);

}

ResponseBodyAdvice用于对写入的数据进行修改，通过ResponseBodyAdvice我们可以很方便的将json数据改成jsonp进行返回。下面我自定义了一个JsonpAdvice用于处理根据header参数返回jsonp格式的数据。代码如下：

import javax.servlet.http.HttpServletRequest;

import org.apache.commons.lang3.StringUtils;
import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.converter.json.MappingJacksonValue;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.http.server.ServletServerHttpRequest;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.AbstractMappingJacksonResponseBodyAdvice;

/**
 * 处理需要返回jsonp的Advice 功能描述:
 * 
 * @version 2.0.0
 * @author zhiminchen
 */
@ControllerAdvice
public class JsonpAdvice extends AbstractMappingJacksonResponseBodyAdvice {

    @Override
    protected void beforeBodyWriteInternal(MappingJacksonValue bodyContainer,
                                           MediaType contentType,
                                           MethodParameter returnType,
                                           ServerHttpRequest request,
                                           ServerHttpResponse response) {

        HttpServletRequest servletRequest = ((ServletServerHttpRequest) request).getServletRequest();
        // 根据 header是否有callback参数决定是否返回jsonp格式的数据
        String callback = servletRequest.getHeader("callback");
        if (StringUtils.isNotBlank(callback)) {
            MediaType contentTypeToUse = getContentType(contentType, request, response);
            response.getHeaders().setContentType(contentTypeToUse);
            bodyContainer.setJsonpFunction(callback);
        }
    }

    protected MediaType getContentType(MediaType contentType,
                                       ServerHttpRequest request,
                                       ServerHttpResponse response) {
        return new MediaType("application", "javascript");
    }

}

如果采用的是FastJsonHttpMessageConverter作为类型转换器。上面的JsonpAdvice 不起作用，我们可以再自定义一个争对FastJsonHttpMessageConverter的Jsonp拦截器，代码如下：

import javax.servlet.http.HttpServletRequest;

import org.apache.commons.lang3.StringUtils;
import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.http.server.ServletServerHttpRequest;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;

import com.alibaba.fastjson.JSONPObject;
import com.pptv.frame.dto.common.ResponseDTO;

/**
 * 处理需要返回jsonp的Advice 功能描述:
 * 
 * @version 2.0.0
 * @author zhiminchen
 */
@ControllerAdvice
public class JsonpAdvice implements ResponseBodyAdvice {

    @Override
    public boolean supports(MethodParameter returnType,
                            Class converterType) {
        return returnType.getMethod().getReturnType().equals(ResponseDTO.class);
    }

    @Override
    public Object beforeBodyWrite(Object body,
                                  MethodParameter returnType,
                                  MediaType selectedContentType,
                                  Class selectedConverterType,
                                  ServerHttpRequest request,
                                  ServerHttpResponse response) {

        HttpServletRequest servletRequest = ((ServletServerHttpRequest) request).getServletRequest();
        String callback = servletRequest.getHeader("callback");
        if (StringUtils.isNotBlank(callback)) {
            MediaType contentTypeToUse = getContentType(request, response);
            response.getHeaders().setContentType(contentTypeToUse);
            JSONPObject jsonpObject = new JSONPObject(callback);
            jsonpObject.addParameter(body);
            return jsonpObject;
        } else {
            return body;
        }
    }

    protected MediaType getContentType(ServerHttpRequest request,
                                       ServerHttpResponse response) {
        return new MediaType("application", "javascript");
    }

}

总结：

Spring MVC通过@ControllerAdvice配合@ExceptionHandler能够统一处理系统的异常信息。
ControllerAdvice配合RequestBodyAdvice与ResponseBodyAdvice可以方便的对请求参数与返回值进行修改。

Spring MVC ControllerAdvice深入解析

ControllerAdvice的简单使用

Spring MVC是如何处理异常的

RequestBodyAdvice与ResponseBodyAdvice

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