SpringMVC 解读——详解编程语言

一：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。请看下面的解析类：

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

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？
RequestMappingHandlerMapping ，BeanNameUrlHandlerMapping是HandlerMapping接口的实现类，[email protected][email protected]url。

RequestMappingHandlerAdapter，HttpRequestHandlerAdapter，SimpleControllerHandlerAdapter是用来处理请求的。具体点说就是确定调用哪个co[email protected]ntroller注解的处理器，支持自定义方法参数和返回值。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。

ExceptionHandlerExceptionResolver，ResponseStatusExceptionResolver，DefaultHandlerExceptionResolver是用来处理异常的解析器。

二：具体实体：

    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("order", 0);   
            handlerMappingDef.getPropertyValues().add("removeSemicolonContent", false);   
            handlerMappingDef.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);   
            String methodMappingName = parserContext.getReaderContext().registerWithGeneratedName(handlerMappingDef);   
            //第二个在这 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);   
            //异常处理解析器   
            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);   
            //异常处理解析器   
            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);   
            //异常处理解析器   
            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));   
            //这里注册了BeanNameUrlHandlerMapping，SimpleControllerHandlerAdapter等   
            // Ensure BeanNameUrlHandlerMapping (SPR-8289) and default HandlerAdapters are not "turned off"   
            MvcNamespaceUtils.registerDefaultComponents(parserContext, source);   
        
            parserContext.popAndRegisterContainingComponent();   
        
            return null;   
        }   
    //在这啊。   
    public static void registerDefaultComponents(ParserContext parserContext, Object source) {   
            registerBeanNameUrlHandlerMapping(parserContext, source);   
            registerHttpRequestHandlerAdapter(parserContext, source);   
            registerSimpleControllerHandlerAdapter(parserContext, source);   
        }  

三：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？
我们主要说明里面的两个：RequestMappingHandler和RequestMappingHandlerAdapter。
第一个是HandlerMapping的实现类，[email protected] 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。
那么它跟<context:component-scan/>有什么区别呢？<context:component-scan/>标签是告诉Spring 来扫描指定包下的类，[email protected]，@Controller，@Service，@Repository等注解标记的组件。
而<mvc:annotation-driven/>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。

转至：http://blog.csdn.net/lovesomnus/article/details/49801593