【Spring MVC】<mvc:annotation-driven/>详解
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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。第一篇文章中说过了,所有的自定义命名空间(像mvc,context等)下的标签解析都是由BeanDefinitionParser接口的子类来完成的。参看第一篇文章中的图片
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
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?
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
光说无凭据,我们直接看代码:
- 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);
-
- 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);
-
- 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);
-
- 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);
-
- 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(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));
-
-
- MvcNamespaceUtils.registerDefaultComponents(parserContext, source);
-
- parserContext.popAndRegisterContainingComponent();
-
- return null;
- }
-
- public static void registerDefaultComponents(ParserContext parserContext, Object source) {
- registerBeanNameUrlHandlerMapping(parserContext, source);
- registerHttpRequestHandlerAdapter(parserContext, source);
- registerSimpleControllerHandlerAdapter(parserContext, source);
- }
略长,但很容易看明白的代码。看注释我们发现,它的确注册了上面说的那几个类。
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,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。
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。
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