SpringMVC 解读——<mvc:annotation-driven/>

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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，用来处理请求映射的。其中第一个是处理@RequestMapping注的。第二个会将controller类的名字映射为请求url。

RequestMappingHandlerAdapter，HttpRequestHandlerAdapter，SimpleControllerHandlerAdapter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。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，它会处理@RequestMapping 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，并注册被@Component，@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

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