mvc:annotation-driven标签
Description : Configures the annotation-driven Spring MVC Controller programming model. Note that this tag works in Web MVC only, not in Portlet MVC!
See org.springframework.web.servlet.config.annotation.EnableWebMvc javadoc for details on code-based alternatives to enabling annotation-driven Spring MVC support.
来自Stackoverflow
The mvc:annotationDriven tag essentially sets you your Spring context to allow for dispatching requests to Controllers.
这个标签本质上设置Spring上下文允许为Controller转发请求
The tag will configure two beans DefaultAnnotationHandlerMapping and AnnotationMethodHandlerAdapter.
这个标签会自动配置两个bean，分别是DefaultAnnotatationHandlerMapping和AnnotataionMethodHanderAdapter.
DefaultAnnotationHanderMapping
Implementation of the {@link org.springframework.web.servlet.HandlerMapping}interface that maps handlers based on HTTP paths expressed through the {@link RequestMapping} annotation at the type or method level.
这个Bean实现了HandlerMapping接口，通过@RequestMapping注解上的Http路径来映射请求处理器。
AnnotataionMethodHanderAdapter
Implementation of the {@link org.springframework.web.servlet.HandlerAdapter} interface
that maps handler methods based on HTTP paths, HTTP methods and request parameters expressed through the {@link RequestMapping} annotation.
这个Bean实现了HandlerAdaper接口，通过@RequestMappingHttp上的Http路径，HttpMethod，请求参数来映射处理类的方法。
DispatcherServlet在使用HandleMapping返回HandlerExecutionChain,HandlerExecutionChain包含的是一个Handler类型的对象，但是没有限定它的具体类型，只要能处理web请求就行了，不一定是Controller类型。对于DispatcherServlet，它不知道如何判断Handler的类型，以及调用Handler的什么方法来处理请求，硬编码是不合适的，也没办法枚举出所有的类型（开发者可以自定义Handler类型），为了屏蔽不同Handler之间的差异，因此DispatcherServlet将Handler的调用交给HandlerAdaptor类型。
HandlerAdaptor成为DispatcherServlet和Handler之间的“中间人”。
对比
<context:annotation-config> declares support for general annotations such as @Required, @Autowired, @PostConstruct, and so on.
<mvc:annotation-driven /> declares explicit support for annotation-driven MVC controllers (i.e. @RequestMapping, @Controller, although support for those is the default behaviour), as well as adding support for declarative validation via @Valid and message body marshalling with @RequestBody/ResponseBody.
