一、AnnotationDrivenBeanDefinitionParser

通過注解的方式開發(fā)Spring MVC，要在***-servlet.xml中加入<mvc:annotation-driven/>標(biāo)簽。
先找到它的解析類。所有自定義命名空間（像mvc，context等）標(biāo)簽解析都是由BeanDefinitionParser接口的子類來完成的默刚。

• RequestMappingHandlerMapping
• BeanNameUrlHandlerMapping
• RequestMappingHandlerAdapter
• HttpRequestHandlerAdapter
• SimpleControllerHandlerAdapter
• ExceptionHandlerExceptionResolver
• ResponseStatusExceptionResolver
• DefaultHandlerExceptionResolver

前兩個是HandlerMapping接口的實(shí)現(xiàn)類逃魄，用來處理請求映射的羡棵。其中第一個是處理@RequestMapping注解的。第二個會將controller類的名字映射為請求url嗅钻。
中間三個是用來處理請求的皂冰。確定調(diào)用哪個controller的哪個方法來處理當(dāng)前請求。第一個處理@Controller注解的處理器养篓，支持自定義方法參數(shù)和返回值秃流。第二個是處理繼承HttpRequestHandler的處理器。第三個處理繼承自Controller接口的處理器柳弄。
后面三個是用來處理異常的解析器舶胀。

二、實(shí)現(xiàn)

public BeanDefinition parse(Element element, ParserContext parserContext) {
        Object source = parserContext.extractSource(element);
 
        CompositeComponentDefinition compDefinition = new CompositeComponentDefinition(element.getTagName(), source);
        parserContext.pushContainingComponent(compDefinition);
 
        RuntimeBeanReference contentNegotiationManager = getContentNegotiationManager(element, source, parserContext);
        //第一個在這 RequestMappingHandlerMapping
        RootBeanDefinition handlerMappingDef = new RootBeanDefinition(RequestMappingHandlerMapping.class);
        handlerMappingDef.setSource(source);
        handlerMappingDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        handlerMappingDef.getPropertyValues().add("order", 0);
        handlerMappingDef.getPropertyValues().add("removeSemicolonContent", false);
        handlerMappingDef.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);
        String methodMappingName = parserContext.getReaderContext().registerWithGeneratedName(handlerMappingDef);
        //第二個在這 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);
        if (element.hasAttribute("ignoreDefaultModelOnRedirect")) {
            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);
        String handlerAdapterName = parserContext.getReaderContext().registerWithGeneratedName(handlerAdapterDef);
        //異常處理解析器
        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);
        String methodExceptionResolverName =
                parserContext.getReaderContext().registerWithGeneratedName(exceptionHandlerExceptionResolver);
        //異常處理解析器
        RootBeanDefinition responseStatusExceptionResolver = new RootBeanDefinition(ResponseStatusExceptionResolver.class);
        responseStatusExceptionResolver.setSource(source);
        responseStatusExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        responseStatusExceptionResolver.getPropertyValues().add("order", 1);
        String responseStatusExceptionResolverName =
                parserContext.getReaderContext().registerWithGeneratedName(responseStatusExceptionResolver);
        //異常處理解析器
        RootBeanDefinition defaultExceptionResolver = new RootBeanDefinition(DefaultHandlerExceptionResolver.class);
        defaultExceptionResolver.setSource(source);
        defaultExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        defaultExceptionResolver.getPropertyValues().add("order", 2);
        String defaultExceptionResolverName =
                parserContext.getReaderContext().registerWithGeneratedName(defaultExceptionResolver);
 
        parserContext.registerComponent(new BeanComponentDefinition(handlerMappingDef, methodMappingName));
        parserContext.registerComponent(new BeanComponentDefinition(handlerAdapterDef, handlerAdapterName));
        parserContext.registerComponent(new BeanComponentDefinition(exceptionHandlerExceptionResolver, methodExceptionResolverName));
        parserContext.registerComponent(new BeanComponentDefinition(responseStatusExceptionResolver, responseStatusExceptionResolverName));
        parserContext.registerComponent(new BeanComponentDefinition(defaultExceptionResolver, defaultExceptionResolverName));
        parserContext.registerComponent(new BeanComponentDefinition(mappedCsInterceptorDef, mappedInterceptorName));
        //這里注冊了BeanNameUrlHandlerMapping碧注，SimpleControllerHandlerAdapter等
        // Ensure BeanNameUrlHandlerMapping (SPR-8289) and default HandlerAdapters are not "turned off"
        MvcNamespaceUtils.registerDefaultComponents(parserContext, source);
 
        parserContext.popAndRegisterContainingComponent();
 
        return null;
    }
//在這啊嚣伐。
public static void registerDefaultComponents(ParserContext parserContext, Object source) {
        registerBeanNameUrlHandlerMapping(parserContext, source);
        registerHttpRequestHandlerAdapter(parserContext, source);
        registerSimpleControllerHandlerAdapter(parserContext, source);
    }

三、總結(jié)

RequestMappingHandlerMapping和RequestMappingHandlerAdapter:第一個是HandlerMapping的實(shí)現(xiàn)類萍丐，它會處理@RequestMapping注解轩端，并將其注冊到請求映射表中。
第二個是HandlerAdapter的實(shí)現(xiàn)類逝变，它是處理請求的適配器基茵，說白了奋构，就是確定調(diào)用哪個類的哪個方法，并且構(gòu)造方法參數(shù)拱层，返回值弥臼。
<context:component-scan/>標(biāo)簽是告訴Spring掃描指定包下的類，并注冊被@Component根灯，@Controller径缅，@Service，@Repository等注解標(biāo)記的組件烙肺。
<mvc:annotation-scan/>是告知Spring啟用注解驅(qū)動纳猪。然后Spring會自動為我們注冊上面說到的幾個Bean到工廠中，來處理我們的請求茬高。