源码解读

我们直接进入正题，进入parse方法中：

public BeanDefinition parse(Element element, ParserContext parserContext) {
		Object source = parserContext.extractSource(element);

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

		RootBeanDefinition methodMappingDef = new RootBeanDefinition(RequestMappingHandlerMapping.class);
		methodMappingDef.setSource(source);
		methodMappingDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
		methodMappingDef.getPropertyValues().add("order", 0);
		String methodMappingName = parserContext.getReaderContext().registerWithGeneratedName(methodMappingDef);

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

		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, source, parserContext);
		ManagedList returnValueHandlers = getReturnValueHandlers(element, source, parserContext);

		RootBeanDefinition methodAdapterDef = new RootBeanDefinition(RequestMappingHandlerAdapter.class);
		methodAdapterDef.setSource(source);
		methodAdapterDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
		methodAdapterDef.getPropertyValues().add("webBindingInitializer", bindingDef);
		methodAdapterDef.getPropertyValues().add("messageConverters", messageConverters);
		if (element.hasAttribute("ignoreDefaultModelOnRedirect")) {
			Boolean ignoreDefaultModel = Boolean.valueOf(element.getAttribute("ignoreDefaultModelOnRedirect"));
			methodAdapterDef.getPropertyValues().add("ignoreDefaultModelOnRedirect", ignoreDefaultModel);
		}
		if (argumentResolvers != null) {
			methodAdapterDef.getPropertyValues().add("customArgumentResolvers", argumentResolvers);
		}
		if (returnValueHandlers != null) {
			methodAdapterDef.getPropertyValues().add("customReturnValueHandlers", returnValueHandlers);
		}
		String methodAdapterName = parserContext.getReaderContext().registerWithGeneratedName(methodAdapterDef);

		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 = parserContext.getReaderContext().registerWithGeneratedName(mappedCsInterceptorDef);

		RootBeanDefinition methodExceptionResolver = new RootBeanDefinition(ExceptionHandlerExceptionResolver.class);
		methodExceptionResolver.setSource(source);
		methodExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
		methodExceptionResolver.getPropertyValues().add("messageConverters", messageConverters);
		methodExceptionResolver.getPropertyValues().add("order", 0);
		String methodExceptionResolverName =
				parserContext.getReaderContext().registerWithGeneratedName(methodExceptionResolver);

		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);

		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(methodMappingDef, methodMappingName));
		parserContext.registerComponent(new BeanComponentDefinition(methodAdapterDef, methodAdapterName));
		parserContext.registerComponent(new BeanComponentDefinition(methodExceptionResolver, 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;
	}

重点看标红的一段，都为我们注册了那些组件，AnnontationmethodMapping,AnnotationmethodAdapter,以及在在最后一行中注册了 ControllerClassNameHandlerMapping，

其中还注册了一个拦截器

ConversionServiceExposingInterceptor

该拦截器会在每个请求之前往request中丢入ConversionService。主要用于spring:eval标签的使用。

所以当我们使用了标签后，就不需要再手动加RequestMapping，HandlerAdapter等标签了。

而其中还有

RequestMappingHandlerAdapter
设置了一些属性，包括：messageConverters，argumentResolvers，returnValueHandlers，这些属性将在RequestMappingHandlerAdapter的after Properties Set（）
方法中完成，如下：

	public void afterPropertiesSet() {
		if (this.argumentResolvers == null) {
			List resolvers = getDefaultArgumentResolvers();
			this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
		}
		if (this.initBinderArgumentResolvers == null) {
			List resolvers = getDefaultInitBinderArgumentResolvers();
			this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
		}
		if (this.returnValueHandlers == null) {
			List handlers = getDefaultReturnValueHandlers();
			this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
		}
	}