Spring MVC ControllerAdvice深入解析

weixin_34378969發表於2018-08-10
SpringMVCController

  Spring 在3.2版本後面增加了一個ControllerAdvice註解。網上的資料說的都是ControllerAdvice配合ExceptionHandler註解可以統一處理異常。而Spring MVC是如何做到的資料卻比較少，下面會先給出使用的例子和踩過的一個坑。然後進行相應的原始碼分析，之後再介始ControllerAdvice另外的兩種使用方式。

ControllerAdvice的簡單使用

  • ControllerAdvice配合ExceptionHandler可以統一處理系統的異常，我們先定義一個ExceptionAdvice類用於處理系統的兩種型別的異常。程式碼如下：
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 記錄log日誌
        e.printStackTrace();
        ResponseDTO responseDTO = new ResponseDTO();
        responseDTO.wrapResponse(ServiceCodeEnum.E999998, "陣列越界異常");

        return responseDTO;
    }

    @ExceptionHandler({
                        Exception.class
    })
    @ResponseBody
    public ResponseDTO handleException(Exception e) {
        // TODO 記錄log日誌
        e.printStackTrace();
        ResponseDTO responseDTO = new ResponseDTO();
        responseDTO.wrapResponse(ServiceCodeEnum.E999998, "未知異常");
        return responseDTO;
    }

}
  • Spring mvc 的配置如下(這裡用到了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支援 -->
    <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>

    <!-- 自定義引數轉換 -->
    <bean id="conversionService"
        class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
    </bean>

</beans>

遇到的一個坑是當spring mvc配置檔案不用<mvc:annotation-drive>這個標籤而是手動將RequestMappingHandlerMapping與RequestMappingHandlerAdapter這兩個類讓spring容器管理，上面的ControllerAdvice將不起作用

    <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是如何處理異常的

  下面來看看Spring MVC是如何處理異常的，為什麼我手動配置了RequestMappingHandlerMapping和RequestMappingHandlerAdapter ControllerAdvice就不會對異常進行攔截呢而通過<mvc:annotation-drive>這個標籤就可以呢？我們從Spring MVC的入口看一下異常是如何處理的。下面是關鍵程式碼（關鍵程式碼都有相應的註釋）：

public class DispatcherServlet extends FrameworkServlet {
/**
  *這個方法是Spring MVC的入口方法，可以看到Spring MVC人具體處理流程
 **/
    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;
//這裡有個try，下面的catch就是用於處理異常的
            try {
                              //檢查是否是上傳檔案的請求
                processedRequest = checkMultipart(request);
                multipartRequestParsed = (processedRequest != request);

                // Determine handler for the current request.
//根據請求的request得到HandlerExecutionChain 物件，裡面有Inceptor和相應的Controller
                mappedHandler = getHandler(processedRequest);
                if (mappedHandler == null || mappedHandler.getHandler() == null) {
                    noHandlerFound(processedRequest, response);
                    return;
                }

                // Determine handler adapter for the current request.
//根據配置的HandlerAdapter 對handler進行適配
                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. 
//這裡會呼叫具體的Handler也就是我們寫的Controller
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

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

                applyDefaultViewName(processedRequest, mv);
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }
            catch (Exception ex) {
//上面處理的邏輯有任何的異常，都將會落到這裡，用dispatchException 這個變數接住異常引用
                dispatchException = ex;
            }
            catch (Throwable err) {
//如果拋的是error， 這裡也會把異常給接住 
                // 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);
            }
//具體處理異常的邏輯看來是在這個方法裡了，具體的邏輯看下面的原始碼
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        }
        catch (Exception ex) {
//這是最外面的try，這裡需要處理Inteceptor裡After的邏輯
            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
        }
        catch (Throwable err) {
//這是最外面的try，這裡需要處理Inteceptor裡After的邏輯
            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);
                }
            }
        }
    }

/**
*這個方法裡processHandlerException用於處理各種不同的Exception
**/
    private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
            HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {

        boolean errorView = false;
//當controller丟擲異常後，就會執行下面的邏輯啦
        if (exception != null) {
            if (exception instanceof ModelAndViewDefiningException) {
                logger.debug("ModelAndViewDefiningException encountered", exception);
                mv = ((ModelAndViewDefiningException) exception).getModelAndView();
            }
            else {
//各種不同的異常會走到這裡來處理，processHandlerException的原始碼在下面有詳細的註釋
                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);
        }
    }

/**
**這裡是用於處理Spring MVC異常的入口
**/
    protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
            Object handler, Exception ex) throws Exception {

        // Check registered HandlerExceptionResolvers...
//通過注入的handlerExceptionResolvers來處得具體的Exception，這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;
    }

}

  通過上面的原始碼，我們一步步可以跟蹤到processHandlerException這個方法，這個方法裡通過HandlerExceptionResolver 來處理具體的異常，而當我們手動只配置RequestMappingHandlerMapping和RequestMappingHandlerAdapter時，並沒有配置任何的HandlerExceptionResolver 。也就是為什麼ControllerAdvice不會對異常進行處理了，我們同時也可以想到<mvc:annotation-drive>一定是幫助我們注入了一個HandlerExceptionResolver 類。下面我們通過分析AnnotationDrivenBeanDefinitionParser這個類來看看到底給我們注入的是那個HandlerExceptionResolver，AnnotationDrivenBeanDefinitionParser類就是用於解析<mvc:annotation-drive>標籤的。下面是AnnotationDrivenBeanDefinitionParser的部分原始碼：

package org.springframework.web.servlet.config;

class AnnotationDrivenBeanDefinitionParser implements BeanDefinitionParser {

/**
*parse是這個類的核心方法，它用於解析 annotation-drive標籤裡的內容，根據標籤裡的內容往spring ioc容器裡注入具體的物件。
**/
    @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);
//這裡有我們熟悉的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);

//這裡會注入具體的ConversionService用於將json,xml轉成Spring mvc裡的請求和返回物件
        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也會在這裡注入
        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);

//這裡有我們需要找的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;
    }
}

  通過上面程式碼的分析， 我們可以找到ExceptionHandlerExceptionResolver這個類來用於處理Spring MVC的各種異常，那ExceptionHandlerExceptionResolver具體又是如何跟ControllerAdvice配合使用來處理各種異常的呢?我們來看看ExceptionHandlerExceptionResolver裡的關鍵程式碼：

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

public class ExceptionHandlerExceptionResolver extends AbstractHandlerMethodExceptionResolver
        implements ApplicationContextAware, InitializingBean {
//這裡有個map用於儲存ControllerAdviceBean
    private final Map<ControllerAdviceBean, ExceptionHandlerMethodResolver> exceptionHandlerAdviceCache =
            new LinkedHashMap<ControllerAdviceBean, ExceptionHandlerMethodResolver>();

//這個方法是由spring 容器呼叫的
    @Override
    public void afterPropertiesSet() {
        // Do this first, it may add ResponseBodyAdvice beans
//這個方法裡會處理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);
        }
    }

/**
*這個方法裡會在spring ioc容器裡找出標註了@ControllerAdvice的類，如果有方法標註了@ExceptionHandler會生成一個ExceptionHandlerMethodResolver類用於處理異常並放到exceptionHandlerAdviceCache這個map快取類裡。
**/
    private void initExceptionHandlerAdviceCache() {
        if (getApplicationContext() == null) {
            return;
        }
        if (logger.isDebugEnabled()) {
            logger.debug("Looking for exception mappings: " + getApplicationContext());
        }
//這裡會找到容器裡標註了ControllerAdvice標籤的類
        List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
        AnnotationAwareOrderComparator.sort(adviceBeans);

        for (ControllerAdviceBean adviceBean : adviceBeans) {
//這個構造方法裡會檢查ControllerAdvice類裡是否有@ExceptionHandler標註的方法，在ExceptionHandlerMethodResolver 有個異常的map。
            ExceptionHandlerMethodResolver resolver = new ExceptionHandlerMethodResolver(adviceBean.getBeanType());
            if (resolver.hasExceptionMappings()) {
//如果有@ExceptionHandler方法，會執行下面的邏輯
                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);
                }
            }
        }
    }

/**
** 這個方法會根據exceptionHandlerAdviceCache這個找到具體需要處理異常的方法
*/
    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();
//根據具體的異常找到處理異常的方法，然後呼叫
                Method method = resolver.resolveMethod(exception);
                if (method != null) {
                    return new ServletInvocableHandlerMethod(entry.getKey().resolveBean(), method);
                }
            }
        }

        return null;
    }
}

  ExceptionHandlerExceptionResolver這個類首先會掃描容器裡所有的ControllerAdvice,如果ControllerAdvice標註了@ExceptionHandler會加到一個map快取裡。在處理具體的異常的時候，會去這個快取裡一個個找是否有ControllerAdvice能夠處理這個異常。整個流程我們就分析到這裡，下面看看ControllerAdvice的另外兩個用法。

RequestBodyAdvice與ResponseBodyAdvice

  Spring在4.2的版本給我們提供了RequestBodyAdvice與ResponseBodyAdvice這兩個介面，而ControllerAdvice是在3.2這個版本里的。那RequestBodyAdvice和ResponseBodyAdvice能夠幫我們做些什麼事性呢？假如現在有個需求，正常介面返回的是json，但傳入的請求頭裡有callback引數需要返回jsonp格式的資料需要如何做呢？下面我們來看看RequestBodyAdvice和ResponseBodyAdvice這兩個類的具體定義，RequestBodyAdvice程式碼如下：

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方法用於決定是否呼叫下面的方法，
    boolean supports(MethodParameter methodParameter, Type targetType,
            Class<? extends HttpMessageConverter<?>> converterType);

//處理空引數據情況
    Object handleEmptyBody(Object body, HttpInputMessage inputMessage, MethodParameter parameter,
            Type targetType, Class<? extends HttpMessageConverter<?>> converterType);

//在引數讀取之前處理的邏輯
    HttpInputMessage beforeBodyRead(HttpInputMessage inputMessage, MethodParameter parameter,
            Type targetType, Class<? extends HttpMessageConverter<?>> converterType) throws IOException;

//在引數讀取之後處理的邏輯
    Object afterBodyRead(Object body, HttpInputMessage inputMessage, MethodParameter parameter,
            Type targetType, Class<? extends HttpMessageConverter<?>> converterType);

}

  從RequestBodyAdvice的定義我們可以清楚的看出他主要用於處理Spring MVC請求引數相關的邏輯，首先定義了support方法用於判斷是否能夠對請求引數做進一步的處理，然後定義了在讀取引數前後方法分別用於處理請求引數。這裡的讀取前後是在Spring MVC呼叫了HttpMessageConverter對引數進行了轉義，所以使用起來還是很方便的。下面來看看ResponseBodyAdvice的定義：

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> {

//這個方法用於判斷是否需要呼叫beforeBodyWrite方法
    boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType);

//這裡在寫入的時候就可以修改要寫入的值啦
    T beforeBodyWrite(T body, MethodParameter returnType, MediaType selectedContentType,
            Class<? extends HttpMessageConverter<?>> selectedConverterType,
            ServerHttpRequest request, ServerHttpResponse response);

}

  ResponseBodyAdvice用於對寫入的資料進行修改，通過ResponseBodyAdvice我們可以很方便的將json資料改成jsonp進行返回。下面我自定義了一個JsonpAdvice用於處理根據header引數返回jsonp格式的資料。程式碼如下：

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;

/**
 * 處理需要返回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();
        // 根據 header是否有callback引數決定是否返回jsonp格式的資料
        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");
    }

}

如果採用的是FastJsonHttpMessageConverter作為型別轉換器。上面的JsonpAdvice 不起作用， 我們可以再自定義一個爭對FastJsonHttpMessageConverter的Jsonp攔截器，程式碼如下：

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;

/**
 * 處理需要返回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");
    }

}

總結：

  • Spring MVC通過@ControllerAdvice配合@ExceptionHandler能夠統一處理系統的異常資訊。
  • ControllerAdvice配合RequestBodyAdvice與ResponseBodyAdvice可以方便的對請求引數與返回值進行修改。

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