annotation-driven 配置详解

一、前沿

在 Spring MVC 的项目中，我们经常使用 <mvc:annotation-driven> 这个配置，那么这个配置到底是做什么的呢？下面来分析一下，首先找到 mvc 的命名空间的定义，如下图：

从上述图中可知，annotation-driven 配置的实现类应该是定义在了 MvcNamespaceHandler 类中，是不是这样的呢？下面我们看下 MvcNamespaceHandler 源码

二、MvcNamespaceHandler

MvcNamespaceHandler 源码如下：

/*** {@link NamespaceHandler} for Spring MVC configuration namespace.** @author Keith Donald* @author Jeremy Grelle* @author Sebastien Deleuze* @since 3.0*/
public class MvcNamespaceHandler extends NamespaceHandlerSupport {@Overridepublic void init() {// 注册 annotation-driven 标签的解析器 AnnotationDrivenBeanDefinitionParser，用来解析 ControllerregisterBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());// 注册 default-servlet-handler 标签的解析器 DefaultServletHandlerBeanDefinitionParser，用来解析静态资源文件（html、jsp、js和css等）registerBeanDefinitionParser("default-servlet-handler", new DefaultServletHandlerBeanDefinitionParser());// 注册 interceptors 标签的解析器 InterceptorsBeanDefinitionParser，用来解析拦截器registerBeanDefinitionParser("interceptors", new InterceptorsBeanDefinitionParser());// 注册 resources 标签的解析器 ResourcesBeanDefinitionParser，用来解析资源文件registerBeanDefinitionParser("resources", new ResourcesBeanDefinitionParser());// 注册 view-controller、redirect-view-controller、status-controller 标签的解析器 ViewControllerBeanDefinitionParser，用来解析视图viewregisterBeanDefinitionParser("view-controller", new ViewControllerBeanDefinitionParser());registerBeanDefinitionParser("redirect-view-controller", new ViewControllerBeanDefinitionParser());registerBeanDefinitionParser("status-controller", new ViewControllerBeanDefinitionParser());// 注册 view-resolvers 标签的解析器 ViewResolversBeanDefinitionParser，用来解析视图解析器registerBeanDefinitionParser("view-resolvers", new ViewResolversBeanDefinitionParser());registerBeanDefinitionParser("tiles-configurer", new TilesConfigurerBeanDefinitionParser());// 注册 freemarker-configurer 标签的解析器 FreeMarkerConfigurerBeanDefinitionParser，用来解析 freemarker 配置registerBeanDefinitionParser("freemarker-configurer", new FreeMarkerConfigurerBeanDefinitionParser());// 注册 groovy-configurer 标签的解析器 GroovyMarkupConfigurerBeanDefinitionParser，用来解析 groovy 配置registerBeanDefinitionParser("groovy-configurer", new GroovyMarkupConfigurerBeanDefinitionParser());// 注册 script-template-configurer 标签的解析器 ScriptTemplateConfigurerBeanDefinitionParser，用来解析 script 脚本模板配置registerBeanDefinitionParser("script-template-configurer", new ScriptTemplateConfigurerBeanDefinitionParser());// 注册 cors 标签的解析器 CorsBeanDefinitionParser，用来解析跨域registerBeanDefinitionParser("cors", new CorsBeanDefinitionParser());}}

从上述源码中可知 annotation-driven 配置对应的解析类 AnnotationDrivenBeanDefinitionParser 确实是定义在 MvcNamespaceHandler 的 init 方法中，那么 annotation-driven 配置实现的具体业务肯定在 AnnotationDrivenBeanDefinitionParser 类中，下面我们分析一下 AnnotationDrivenBeanDefinitionParser 源码

三、AnnotationDrivenBeanDefinitionParser

AnnotationDrivenBeanDefinitionParser 的 parse 方法实现了具体的解析逻辑，源码如下：

/*** A {@link BeanDefinitionParser} that provides the configuration for the* {@code <annotation-driven/>} MVC namespace element.** <p>This class registers the following {@link HandlerMapping HandlerMappings}:</p>* <ul>* <li>{@link RequestMappingHandlerMapping}* 将请求映射到带注解的控制器方法时，按照0排序，例如 @RequestMapping("/test")* ordered at 0 for mapping requests to annotated controller methods.* <li>{@link BeanNameUrlHandlerMapping}* 将URL路径映射到控制器bean名称时，按照2排序* 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 HandlerAdapters}:* <ul>* <li>{@link RequestMappingHandlerAdapter}* 处理带有@controller注解的适配器（支持自定义的参数和返回值），对应于 RequestMappingHandlerMapping，例如 @RequestMapping("/test")* for processing requests with annotated controller methods.* <li>{@link HttpRequestHandlerAdapter}* 处理带有 HttpRequestHandlers 的适配器* for processing requests with {@link HttpRequestHandler HttpRequestHandlers}.* <li>{@link SimpleControllerHandlerAdapter}* 处理基于 Controllers 接口的适配器* for processing requests with interface-based {@link Controller Controllers}.* </ul>** 异常处理器* <p>This class registers the following {@link HandlerExceptionResolver HandlerExceptionResolvers}:* <ul>* <li>{@link ExceptionHandlerExceptionResolver} for handling exceptions through* {@link org.springframework.web.bind.annotation.ExceptionHandler} methods.* <li>{@link ResponseStatusExceptionResolver} for exceptions annotated* with {@link org.springframework.web.bind.annotation.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 HttpMessageConverters} depending on which third-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*/
class AnnotationDrivenBeanDefinitionParser implements BeanDefinitionParser {@Override@Nullablepublic BeanDefinition parse(Element element, ParserContext context) {Object source = context.extractSource(element);XmlReaderContext readerContext = context.getReaderContext();CompositeComponentDefinition compDefinition = new CompositeComponentDefinition(element.getTagName(), source);context.pushContainingComponent(compDefinition);RuntimeBeanReference contentNegotiationManager = getContentNegotiationManager(element, source, context);// 定义 RequestMappingHandlerMappingRootBeanDefinition handlerMappingDef = new RootBeanDefinition(RequestMappingHandlerMapping.class);handlerMappingDef.setSource(source);handlerMappingDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);// 排序值为 0handlerMappingDef.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);}configurePathMatchingProperties(handlerMappingDef, element, context);// 注册 RequestMappingHandlerMapping 类型对应的 RootBeanDefinitionreaderContext.getRegistry().registerBeanDefinition(HANDLER_MAPPING_BEAN_NAME, handlerMappingDef);RuntimeBeanReference corsRef = MvcNamespaceUtils.registerCorsConfigurations(null, context, source);handlerMappingDef.getPropertyValues().add("corsConfigurations", corsRef);RuntimeBeanReference conversionService = getConversionService(element, source, context);RuntimeBeanReference validator = getValidator(element, source, context);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, context);ManagedList<?> argumentResolvers = getArgumentResolvers(element, context);ManagedList<?> returnValueHandlers = getReturnValueHandlers(element, context);String asyncTimeout = getAsyncTimeout(element);RuntimeBeanReference asyncExecutor = getAsyncExecutor(element);ManagedList<?> callableInterceptors = getCallableInterceptors(element, source, context);ManagedList<?> deferredResultInterceptors = getDeferredResultInterceptors(element, source, context);// 定义 RequestMappingHandlerAdapterRootBeanDefinition handlerAdapterDef = new RootBeanDefinition(RequestMappingHandlerAdapter.class);handlerAdapterDef.setSource(source);handlerAdapterDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);handlerAdapterDef.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);handlerAdapterDef.getPropertyValues().add("webBindingInitializer", bindingDef);// 消息转换器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);}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);// 注册 RequestMappingHandlerAdapter 对应的 RootBeanDefinitionreaderContext.getRegistry().registerBeanDefinition(HANDLER_ADAPTER_BEAN_NAME, handlerAdapterDef);RootBeanDefinition uriContributorDef =new RootBeanDefinition(CompositeUriComponentsContributorFactoryBean.class);uriContributorDef.setSource(source);uriContributorDef.getPropertyValues().addPropertyValue("handlerAdapter", handlerAdapterDef);uriContributorDef.getPropertyValues().addPropertyValue("conversionService", conversionService);String uriContributorName = MvcUriComponentsBuilder.MVC_URI_COMPONENTS_CONTRIBUTOR_BEAN_NAME;readerContext.getRegistry().registerBeanDefinition(uriContributorName, uriContributorDef);RootBeanDefinition csInterceptorDef = new RootBeanDefinition(ConversionServiceExposingInterceptor.class);csInterceptorDef.setSource(source);csInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(0, conversionService);RootBeanDefinition mappedInterceptorDef = new RootBeanDefinition(MappedInterceptor.class);mappedInterceptorDef.setSource(source);mappedInterceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);mappedInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(0, (Object) null);mappedInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(1, csInterceptorDef);String mappedInterceptorName = readerContext.registerWithGeneratedName(mappedInterceptorDef);// 定义 ExceptionHandlerExceptionResolver 异常处理器RootBeanDefinition methodExceptionResolver = new RootBeanDefinition(ExceptionHandlerExceptionResolver.class);methodExceptionResolver.setSource(source);methodExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);methodExceptionResolver.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);methodExceptionResolver.getPropertyValues().add("messageConverters", messageConverters);// 排序值为 0methodExceptionResolver.getPropertyValues().add("order", 0);addResponseBodyAdvice(methodExceptionResolver);if (argumentResolvers != null) {methodExceptionResolver.getPropertyValues().add("customArgumentResolvers", argumentResolvers);}if (returnValueHandlers != null) {methodExceptionResolver.getPropertyValues().add("customReturnValueHandlers", returnValueHandlers);}String methodExResolverName = readerContext.registerWithGeneratedName(methodExceptionResolver);// 定义 ResponseStatusExceptionResolver 返回状态异常解析器RootBeanDefinition statusExceptionResolver = new RootBeanDefinition(ResponseStatusExceptionResolver.class);statusExceptionResolver.setSource(source);statusExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);// 排序值为 1statusExceptionResolver.getPropertyValues().add("order", 1);String statusExResolverName = readerContext.registerWithGeneratedName(statusExceptionResolver);// 定义Spring中已知的异常解析器RootBeanDefinition defaultExceptionResolver = new RootBeanDefinition(DefaultHandlerExceptionResolver.class);defaultExceptionResolver.setSource(source);defaultExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);// 排序值为 2defaultExceptionResolver.getPropertyValues().add("order", 2);String defaultExResolverName = readerContext.registerWithGeneratedName(defaultExceptionResolver);// 将上面所有的 bean 组件注册到上下文中context.registerComponent(new BeanComponentDefinition(handlerMappingDef, HANDLER_MAPPING_BEAN_NAME));context.registerComponent(new BeanComponentDefinition(handlerAdapterDef, HANDLER_ADAPTER_BEAN_NAME));context.registerComponent(new BeanComponentDefinition(uriContributorDef, uriContributorName));context.registerComponent(new BeanComponentDefinition(mappedInterceptorDef, mappedInterceptorName));context.registerComponent(new BeanComponentDefinition(methodExceptionResolver, methodExResolverName));context.registerComponent(new BeanComponentDefinition(statusExceptionResolver, statusExResolverName));context.registerComponent(new BeanComponentDefinition(defaultExceptionResolver, defaultExResolverName));// Ensure BeanNameUrlHandlerMapping (SPR-8289) and default HandlerAdapters are not "turned off"// 注册默认的一些组件，例如 BeanNameUrlHandlerMapping、HttpRequestHandlerAdapter、// SimpleControllerHandlerAdapter 和 HandlerMappingIntrospectorMvcNamespaceUtils.registerDefaultComponents(context, source);context.popAndRegisterContainingComponent();return null;}
}

从上述源码中可以看出，在 AnnotationDrivenBeanDefinitionParser 中主要实现了注册了很多 bean 的功能，其中我们最关心的就是 RequestMappingHandlerMapping 和 RequestMappingHandlerAdapter 两个类，功能分别如图：

RequestMappingHandlerMapping ： HandlerMapping 的实现类，它处理的是 @RequestMapping 注解，并将其注册到映射表中，即 url 对应的 Controller 的方法

RequestMappingHandlerAdapter ： HandlerAdapter 的实现类，它是处理请求的适配器，就是确定调用哪个 Controller 的哪个方法

到这里，AnnotationDrivenBeanDefinitionParser 的源码就分析完了，其中没有什么太多复杂的逻辑，代码注释都写清楚了

四、annotation-driven 作用

通过阅读 AnnotationDrivenBeanDefinitionParser 的源码可知，annotation-driven 配置的作用如下：

1）、主要是注册了 RequestMappingHandlerMapping 和 RequestMappingHandlerAdapter bean，存储了请求url到Controller方法的映射关系

2）、注册了异常处理器

五、总结

Spring MVC 中如果配置了 <mvc:annotation-driven> ，则所有的 Controller 就会被解析，所以相应的 .do 请求就会被 Controller 处理，因此这个配置至关重要。当请求没有匹配到处理类（其中包括没有配置 <mvc:annotation-driven> 或者访问的是静态资源文件）时，就会去找 <mvc:default-servlet-handler> （处理静态资源文件）配置的 DefaultServletHttpRequestHandler 默认处理器处理了