SpringMVC

【1】AnnotationDrivenBeanDefinitionParser

通常如果我们希望通过注解的方式来进行Spring MVC开发，我们都会在***-servlet.xml中加入<mvc:annotation-driven/>标签来告诉Spring我们的目的。

但是我们为什么这么做呢？这个标签是什么意思呢？它做了什么呢？

同样为了弄清楚这些问题， 像<context:component-scan/>标签一样，我们先找到它的解析类。前面说过了，所有的自定义命名空间（像mvc，context等）下的标签解析都是由BeanDefinitionParser接口的子类来完成的。

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查看BeanDefinitionParser说明：

该接口被默认bean定义文档阅读者使用以处理自定义和顶级(直属<beans/>)标签。

实现者可以自由地将标签里面的元数据转化成许多需要的BeanDefinition。

解析器从标签隶属的namespace对应的NamespaceHandler找到合适的BeanDefinitonParser，

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该解析器的实现类有：

我们看到有多个AnnotationDrivenBeanDefinitionParser，他们是用来处理不同命名空间下的标签的，我们今天研究<annotation-driven/>的是<mvc:annotation-driven/>标签，所以我们找到对应的实现类是org.springframework.web.servlet.config.AnnotationDrivenBeanDefinitionParser。

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AnnotationDrivenBeanDefinitionParser的文档说明如下：

 * A {@link BeanDefinitionParser} that provides the configuration for the * {@code <annotation-driven/>} MVC namespace element. * * <p>This class registers the following {@link HandlerMapping}s:</p> * <ul> * <li>{@link RequestMappingHandlerMapping} * ordered at 0 for mapping requests to annotated controller methods. * <li>{@link BeanNameUrlHandlerMapping} * ordered at 2 to map URL paths to controller bean names. * </ul> * * <p><strong>Note:</strong> Additional HandlerMappings may be registered * as a result of using the {@code <view-controller>} or the * {@code <resources>} MVC namespace elements. * * <p>This class registers the following {@link HandlerAdapter}s: * <ul> * <li>{@link RequestMappingHandlerAdapter} * for processing requests with annotated controller methods. * <li>{@link HttpRequestHandlerAdapter} * for processing requests with {@link HttpRequestHandler}s. * <li>{@link SimpleControllerHandlerAdapter} * for processing requests with interface-based {@link Controller}s. * </ul> * * <p>This class registers the following {@link HandlerExceptionResolver}s: * <ul> * <li>{@link ExceptionHandlerExceptionResolver} for handling exceptions * through @{@link ExceptionHandler} methods. * <li>{@link ResponseStatusExceptionResolver} for exceptions annotated * with @{@link ResponseStatus}. * <li>{@link DefaultHandlerExceptionResolver} for resolving known Spring * exception types * </ul> * * <p>This class registers an {@link org.springframework.util.AntPathMatcher} * and a {@link org.springframework.web.util.UrlPathHelper} to be used by: * <ul> * <li>the {@link RequestMappingHandlerMapping}, * <li>the {@link HandlerMapping} for ViewControllers * <li>and the {@link HandlerMapping} for serving resources * </ul> * Note that those beans can be configured by using the {@code path-matching} MVC namespace element. * * <p>Both the {@link RequestMappingHandlerAdapter} and the * {@link ExceptionHandlerExceptionResolver} are configured with instances of * the following by default: * <ul> * <li>A {@link ContentNegotiationManager} * <li>A {@link DefaultFormattingConversionService} * <li>A {@link org.springframework.validation.beanvalidation.LocalValidatorFactoryBean} * if a JSR-303 implementation is available on the classpath * <li>A range of {@link HttpMessageConverter}s depending on what 3rd party * libraries are available on the classpath. * </ul> * * @author Keith Donald * @author Juergen Hoeller * @author Arjen Poutsma * @author Rossen Stoyanchev * @author Brian Clozel * @author Agim Emruli * @since 3.0

该注释文档说明该解析器想容器中注入了如下类：

• RequestMappingHandlerMapping

• BeanNameUrlHandlerMapping

• RequestMappingHandlerAdapter

• HttpRequestHandlerAdapter

• SimpleControllerHandlerAdapter

• ExceptionHandlerExceptionResolver

• ResponseStatusExceptionResolver

• DefaultHandlerExceptionResolver

上面几个Bean实例。这几个类都是用来做什么的呢？

前两个是HandlerMapping接口的实现类，用来处理请求映射的。

其中第一个是处理@RequestMapping注解的。.
第二个会将controller类的名字映射为请求url。

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中间三个是用来处理请求的。具体点说就是确定调用哪个controller的哪个方法来处理当前请求。

第一个处理@Controller注解的处理器，支持自定义方法参数和返回值（很酷）。
第二个是处理继承HttpRequestHandler的处理器。
第三个处理继承自Controller接口的处理器。

后面三个是用来处理异常的解析器。

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【2】代码追溯

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);/*  RequestMappingHandlerMapping order:0*/        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);        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 */        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);/* 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);/* ResponseStatusExceptionResolver */        RootBeanDefinition responseStatusExceptionResolver = new RootBeanDefinition(ResponseStatusExceptionResolver.class);        responseStatusExceptionResolver.setSource(source);        responseStatusExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);        responseStatusExceptionResolver.getPropertyValues().add("order", 1);        String responseStatusExceptionResolverName =                readerContext.registerWithGeneratedName(responseStatusExceptionResolver);/* DefaultHandlerExceptionResolver */        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));/* BeanNameUrlHandlerMapping  HttpRequestHandlerAdapter 和 SimpleControllerHandlerAdapter*/        // Ensure BeanNameUrlHandlerMapping (SPR-8289) and default HandlerAdapters are not "turned off"        MvcNamespaceUtils.registerDefaultComponents(parserContext, source);        parserContext.popAndRegisterContainingComponent();        return null;    }

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注册默认mapping和adapter方法如下：

    public static void registerDefaultComponents(ParserContext parserContext, Object source) {        registerBeanNameUrlHandlerMapping(parserContext, source);        registerHttpRequestHandlerAdapter(parserContext, source);        registerSimpleControllerHandlerAdapter(parserContext, source);    }

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【3】总结

我们知道了它们自动为我们注册了这么多的Bean，那这些Bean是做什么的呢？

主要说明里面的两个，RequestMappingHandlerMapping和RequestMappingHandlerAdapter。

第一个是HandlerMapping的实现类，它会处理@RequestMapping 注解，并将其注册到请求映射表中。

第二个是HandlerAdapter的实现类，它是处理请求的适配器，说白了，就是确定调用哪个类的哪个方法，并且构造方法参数，返回值。

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那么它跟<context:component-scan/>有什么区别呢？

其实<context:component-scan/>标签是告诉Spring 来扫描指定包下的类，并注册被@Component，@Controller，@Service，@Repository等注解标记的组件（即，项目启动完成前，这些被注解的组件就会被实例化bean放入容器上下文中）。

而<mvc:annotation-driven/>是告知Spring，我们启用注解驱动，为WEB 应用服务(我们就可以使用该标签注册的几个bean的功能)。然后Spring会自动为我们注册上面说到的几个Bean到工厂中，来处理我们的请求。

即，如果不想手动配置bean(xml)，使用注解获取bean，就必须使用<context:component-scan/>。

如果想使web项目正常运转，一般情况下，<mvc:annotation-driven/>是必需的！

项目中二者相辅相成，缺一不可！！！