SpringMVC 解读之<mvc:annotation-driven/>标签

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第零人 2022-12-14 15:38:58 ©著作权

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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
BeanNameUrlHandlerMappingRequestMappingHandlerAdapter
HttpRequestHandlerAdapterSimpleControllerHandlerAdapterExceptionHandlerExceptionResolver
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：

1. public BeanDefinition parse(Element element, ParserContext parserContext) {  
2.         Object source = parserContext.extractSource(element);  
3.    
4. new CompositeComponentDefinition(element.getTagName(), source);  
5.         parserContext.pushContainingComponent(compDefinition);  
6.    
7.         RuntimeBeanReference contentNegotiationManager = getContentNegotiationManager(element, source, parserContext);  
8. //第一个在这 RequestMappingHandlerMapping  
9. new RootBeanDefinition(RequestMappingHandlerMapping.class);  
10.         handlerMappingDef.setSource(source);  
11.         handlerMappingDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);  
12. "order", 0);  
13. "removeSemicolonContent", false);  
14. "contentNegotiationManager", contentNegotiationManager);  
15.         String methodMappingName = parserContext.getReaderContext().registerWithGeneratedName(handlerMappingDef);  
16. //第二个在这 RequestMappingHandlerAdapter  
17. new RootBeanDefinition(RequestMappingHandlerAdapter.class);  
18.         handlerAdapterDef.setSource(source);  
19.         handlerAdapterDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);  
20. "contentNegotiationManager", contentNegotiationManager);  
21. "webBindingInitializer", bindingDef);  
22. "messageConverters", messageConverters);  
23. if (element.hasAttribute("ignoreDefaultModelOnRedirect")) {  
24. "ignoreDefaultModelOnRedirect"));  
25. "ignoreDefaultModelOnRedirect", ignoreDefaultModel);  
26.         }  
27. if (argumentResolvers != null) {  
28. "customArgumentResolvers", argumentResolvers);  
29.         }  
30. if (returnValueHandlers != null) {  
31. "customReturnValueHandlers", returnValueHandlers);  
32.         }  
33. if (asyncTimeout != null) {  
34. "asyncRequestTimeout", asyncTimeout);  
35.         }  
36. if (asyncExecutor != null) {  
37. "taskExecutor", asyncExecutor);  
38.         }  
39. "callableInterceptors", callableInterceptors);  
40. "deferredResultInterceptors", deferredResultInterceptors);  
41.         String handlerAdapterName = parserContext.getReaderContext().registerWithGeneratedName(handlerAdapterDef);  
42. //异常处理解析器  
43. new RootBeanDefinition(ExceptionHandlerExceptionResolver.class);  
44.         exceptionHandlerExceptionResolver.setSource(source);  
45.         exceptionHandlerExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);  
46. "contentNegotiationManager", contentNegotiationManager);  
47. "messageConverters", messageConverters);  
48. "order", 0);  
49.         String methodExceptionResolverName =  
50.                 parserContext.getReaderContext().registerWithGeneratedName(exceptionHandlerExceptionResolver);  
51. //异常处理解析器  
52. new RootBeanDefinition(ResponseStatusExceptionResolver.class);  
53.         responseStatusExceptionResolver.setSource(source);  
54.         responseStatusExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);  
55. "order", 1);  
56.         String responseStatusExceptionResolverName =  
57.                 parserContext.getReaderContext().registerWithGeneratedName(responseStatusExceptionResolver);  
58. //异常处理解析器  
59. new RootBeanDefinition(DefaultHandlerExceptionResolver.class);  
60.         defaultExceptionResolver.setSource(source);  
61.         defaultExceptionResolver.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);  
62. "order", 2);  
63.         String defaultExceptionResolverName =  
64.                 parserContext.getReaderContext().registerWithGeneratedName(defaultExceptionResolver);  
65.    
66. new BeanComponentDefinition(handlerMappingDef, methodMappingName));  
67. new BeanComponentDefinition(handlerAdapterDef, handlerAdapterName));  
68. new BeanComponentDefinition(exceptionHandlerExceptionResolver, methodExceptionResolverName));  
69. new BeanComponentDefinition(responseStatusExceptionResolver, responseStatusExceptionResolverName));  
70. new BeanComponentDefinition(defaultExceptionResolver, defaultExceptionResolverName));  
71. new BeanComponentDefinition(mappedCsInterceptorDef, mappedInterceptorName));  
72. //这里注册了BeanNameUrlHandlerMapping，SimpleControllerHandlerAdapter等  
73. // Ensure BeanNameUrlHandlerMapping (SPR-8289) and default HandlerAdapters are not "turned off"  
74.         MvcNamespaceUtils.registerDefaultComponents(parserContext, source);  
75.    
76.         parserContext.popAndRegisterContainingComponent();  
77.    
78. return null;  
79.     }  
80. //在这啊。  
81. public static void registerDefaultComponents(ParserContext parserContext, Object source) {  
82.         registerBeanNameUrlHandlerMapping(parserContext, source);  
83.         registerHttpRequestHandlerAdapter(parserContext, source);  
84.         registerSimpleControllerHandlerAdapter(parserContext, source);  
85.     }