Spring MVC 之 <context:annotation-driven/>

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版权声明：本文为博主原创文章，转载请注明出处，谢谢!

版权声明：本文为博主原创文章，转载请注明出处：http://blog.jerkybible.com/2015/05/28/Spring MVC 之 contextannotation-driven/

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一、解析类

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中加入标签来告诉Spring我们的目的。找到对应的实现类是org.springframework.web.servlet.config.AnnotationDrivenBeanDefinitionParser。
通过阅读类注释文档，我们发现这个类主要是用来向工厂中注册了

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RequestMappingHandlerMapping 
BeanNameUrlHandlerMapping
RequestMappingHandlerAdapter
HttpRequestHandlerAdapter
SimpleControllerHandlerAdapter
ExceptionHandlerExceptionResolver 
ResponseStatusExceptionResolver 
DefaultHandlerExceptionResolver

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。

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。

二、实现流程

首先进入的是xml解析方法。由于annotation-driven不是默认的命名空间，会进入else，使用delegate解析元素。

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/**
 * Parse the elements at the root level in the document:
 * &quot;import&quot;, &quot;alias&quot;, &quot;bean&quot;.
 * @param root the DOM root element of the document
 */
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
	if (delegate.isDefaultNamespace(root)) {
		NodeList nl = root.getChildNodes();
		for (int i = 0; i &lt; nl.getLength(); i++) {
			Node node = nl.item(i);
			if (node instanceof Element) {
				Element ele = (Element) node;
				if (delegate.isDefaultNamespace(ele)) {
					parseDefaultElement(ele, delegate);
				}
				else {
					delegate.parseCustomElement(ele);
				}
			}
		}
	}
	else {
		delegate.parseCustomElement(root);
	}
}

然后会进入下面的方法。这里的Handler获取的是MvcNamespaceHandler。接着可以看到MvcNamespaceHandler中注册的annotation-driven的Parse是AnnotationDrivenBeanDefinitionParser。最后是Parse方法，该方法比较繁琐但是很好理解，注册了上面说的那几个类。

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public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
	String namespaceUri = getNamespaceURI(ele);
	NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
	if (handler == null) {
		error(&quot;Unable to locate Spring NamespaceHandler for XML schema namespace [&quot; + namespaceUri + &quot;]&quot;, ele);
		return null;
	}
	return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}

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public class MvcNamespaceHandler extends NamespaceHandlerSupport {
@Override
public void init() {
	registerBeanDefinitionParser(&quot;annotation-driven&quot;, new AnnotationDrivenBeanDefinitionParser());
	registerBeanDefinitionParser(&quot;default-servlet-handler&quot;, new DefaultServletHandlerBeanDefinitionParser());
	registerBeanDefinitionParser(&quot;interceptors&quot;, new InterceptorsBeanDefinitionParser());
	registerBeanDefinitionParser(&quot;resources&quot;, new ResourcesBeanDefinitionParser());
	registerBeanDefinitionParser(&quot;view-controller&quot;, new ViewControllerBeanDefinitionParser());
	registerBeanDefinitionParser(&quot;redirect-view-controller&quot;, new ViewControllerBeanDefinitionParser());
	registerBeanDefinitionParser(&quot;status-controller&quot;, new ViewControllerBeanDefinitionParser());
	registerBeanDefinitionParser(&quot;view-resolvers&quot;, new ViewResolversBeanDefinitionParser());
	registerBeanDefinitionParser(&quot;tiles-configurer&quot;, new TilesConfigurerBeanDefinitionParser());
	registerBeanDefinitionParser(&quot;freemarker-configurer&quot;, new FreeMarkerConfigurerBeanDefinitionParser());
	registerBeanDefinitionParser(&quot;velocity-configurer&quot;, new VelocityConfigurerBeanDefinitionParser());
	registerBeanDefinitionParser(&quot;groovy-configurer&quot;, new GroovyMarkupConfigurerBeanDefinitionParser());
}
}
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@Override
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);
        //第一个在这 RequestMappingHandlerMapping
	RootBeanDefinition handlerMappingDef = new RootBeanDefinition(RequestMappingHandlerMapping.class);
	handlerMappingDef.setSource(source);
	handlerMappingDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
	handlerMappingDef.getPropertyValues().add(&quot;order&quot;, 0);
	handlerMappingDef.getPropertyValues().add(&quot;contentNegotiationManager&quot;, contentNegotiationManager);
	String methodMappingName = parserContext.getReaderContext().registerWithGeneratedName(handlerMappingDef);
	if (element.hasAttribute(&quot;enable-matrix-variables&quot;)) {
		Boolean enableMatrixVariables = Boolean.valueOf(element.getAttribute(&quot;enable-matrix-variables&quot;));
		handlerMappingDef.getPropertyValues().add(&quot;removeSemicolonContent&quot;, !enableMatrixVariables);
	}
	else if (element.hasAttribute(&quot;enableMatrixVariables&quot;)) {
		Boolean enableMatrixVariables = Boolean.valueOf(element.getAttribute(&quot;enableMatrixVariables&quot;));
		handlerMappingDef.getPropertyValues().add(&quot;removeSemicolonContent&quot;, !enableMatrixVariables);
	}
	configurePathMatchingProperties(handlerMappingDef, element, parserContext);
	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(&quot;conversionService&quot;, conversionService);
	bindingDef.getPropertyValues().add(&quot;validator&quot;, validator);
	bindingDef.getPropertyValues().add(&quot;messageCodesResolver&quot;, messageCodesResolver);
	ManagedList&lt;?&gt; messageConverters = getMessageConverters(element, source, parserContext);
	ManagedList&lt;?&gt; argumentResolvers = getArgumentResolvers(element, parserContext);
	ManagedList&lt;?&gt; returnValueHandlers = getReturnValueHandlers(element, parserContext);
	String asyncTimeout = getAsyncTimeout(element);
	RuntimeBeanReference asyncExecutor = getAsyncExecutor(element);
	ManagedList&lt;?&gt; callableInterceptors = getCallableInterceptors(element, source, parserContext);
	ManagedList&lt;?&gt; deferredResultInterceptors = getDeferredResultInterceptors(element, source, parserContext);
        //第二个在这 RequestMappingHandlerAdapter
	RootBeanDefinition handlerAdapterDef = new RootBeanDefinition(RequestMappingHandlerAdapter.class);
	handlerAdapterDef.setSource(source);
	handlerAdapterDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
	handlerAdapterDef.getPropertyValues().add(&quot;contentNegotiationManager&quot;, contentNegotiationManager);
	handlerAdapterDef.getPropertyValues().add(&quot;webBindingInitializer&quot;, bindingDef);
	handlerAdapterDef.getPropertyValues().add(&quot;messageConverters&quot;, messageConverters);
	addResponseBodyAdvice(handlerAdapterDef);
	if (element.hasAttribute(&quot;ignore-default-model-on-redirect&quot;)) {
		Boolean ignoreDefaultModel = Boolean.valueOf(element.getAttribute(&quot;ignore-default-model-on-redirect&quot;));
		handlerAdapterDef.getPropertyValues().add(&quot;ignoreDefaultModelOnRedirect&quot;, ignoreDefaultModel);
	}
	else if (element.hasAttribute(&quot;ignoreDefaultModelOnRedirect&quot;)) {
		// &quot;ignoreDefaultModelOnRedirect&quot; spelling is deprecated
		Boolean ignoreDefaultModel = Boolean.valueOf(element.getAttribute(&quot;ignoreDefaultModelOnRedirect&quot;));
		handlerAdapterDef.getPropertyValues().add(&quot;ignoreDefaultModelOnRedirect&quot;, ignoreDefaultModel);
	}
	if (argumentResolvers != null) {
		handlerAdapterDef.getPropertyValues().add(&quot;customArgumentResolvers&quot;, argumentResolvers);
	}
	if (returnValueHandlers != null) {
		handlerAdapterDef.getPropertyValues().add(&quot;customReturnValueHandlers&quot;, returnValueHandlers);
	}
	if (asyncTimeout != null) {
		handlerAdapterDef.getPropertyValues().add(&quot;asyncRequestTimeout&quot;, asyncTimeout);
	}
	if (asyncExecutor != null) {
		handlerAdapterDef.getPropertyValues().add(&quot;taskExecutor&quot;, asyncExecutor);
	}
	handlerAdapterDef.getPropertyValues().add(&quot;callableInterceptors&quot;, callableInterceptors);
	handlerAdapterDef.getPropertyValues().add(&quot;deferredResultInterceptors&quot;, deferredResultInterceptors);
	String handlerAdapterName = parserContext.getReaderContext().registerWithGeneratedName(handlerAdapterDef);
	String uriCompContribName = MvcUriComponentsBuilder.MVC_URI_COMPONENTS_CONTRIBUTOR_BEAN_NAME;
	RootBeanDefinition uriCompContribDef = new RootBeanDefinition(CompositeUriComponentsContributorFactoryBean.class);
	uriCompContribDef.setSource(source);
	uriCompContribDef.getPropertyValues().addPropertyValue(&quot;handlerAdapter&quot;, handlerAdapterDef);
	uriCompContribDef.getPropertyValues().addPropertyValue(&quot;conversionService&quot;, conversionService);
	parserContext.getReaderContext().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 = parserContext.getReaderContext().registerWithGeneratedName(mappedCsInterceptorDef);
	RootBeanDefinition exceptionHandlerExceptionResolver = new RootBeanDefinition(ExceptionHandlerExceptionResolver.class);
	exceptionHandlerExceptionResolver.setSource(source);
	exceptionHandlerExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
	exceptionHandlerExceptionResolver.getPropertyValues().add(&quot;contentNegotiationManager&quot;, contentNegotiationManager);
	exceptionHandlerExceptionResolver.getPropertyValues().add(&quot;messageConverters&quot;, messageConverters);
	exceptionHandlerExceptionResolver.getPropertyValues().add(&quot;order&quot;, 0);
	addResponseBodyAdvice(exceptionHandlerExceptionResolver);
	String methodExceptionResolverName =
			parserContext.getReaderContext().registerWithGeneratedName(exceptionHandlerExceptionResolver);
	RootBeanDefinition responseStatusExceptionResolver = new RootBeanDefinition(ResponseStatusExceptionResolver.class);
	responseStatusExceptionResolver.setSource(source);
	responseStatusExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
	responseStatusExceptionResolver.getPropertyValues().add(&quot;order&quot;, 1);
	String responseStatusExceptionResolverName =
			parserContext.getReaderContext().registerWithGeneratedName(responseStatusExceptionResolver);
	RootBeanDefinition defaultExceptionResolver = new RootBeanDefinition(DefaultHandlerExceptionResolver.class);
	defaultExceptionResolver.setSource(source);
	defaultExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
	defaultExceptionResolver.getPropertyValues().add(&quot;order&quot;, 2);
	String defaultExceptionResolverName =
			parserContext.getReaderContext().registerWithGeneratedName(defaultExceptionResolver);
	parserContext.registerComponent(new BeanComponentDefinition(handlerMappingDef, methodMappingName));
	parserContext.registerComponent(new BeanComponentDefinition(handlerAdapterDef, handlerAdapterName));
	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 &quot;turned off&quot;
	MvcNamespaceUtils.registerDefaultComponents(parserContext, source);
	parserContext.popAndRegisterContainingComponent();
	return null;
}

三、总结
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。（下片文章我们会详细介绍的）

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。（后面文章也会陆续详细介绍的）

那么它跟<context:component-scan/>的区别是，<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。

而<mvc:annotation-scan/>是告知Spring，我们启用注解驱动。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。
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