mvc-HandlerMapping

HandlerMapping：定义了web请求映射和处理器（Handler）之间的映射

类结构：

 

handler的种类：

Servlet
Controller
HttpRequestHandler (Spring Invoke)
Bean  （@RequestMapping）

顶层抽象：
AbstractHandlerMapping：支持sort，默认handler，handler interceptors；关联ApplicationContext ；封装HandlerExecutionChain

URL匹配：

1. AbstractUrlHandlerMapping：支持注册url->hander的映射（直接，模糊）；handerName->handlerBean；
2. AbstractDetectingUrlHandlerMapping：支持从application context中自动发现 handler；启动初始化
3. AbstractControllerUrlHandlerMapping：支持判断是否实现 Controller接口，或者Controller 注解修饰

HandlerMethod匹配：

1. AbstractHandlerMethodMapping：实现 request和HandlerMethod的映射及注册；InitializingBean 启动初始化
2. RequestMappingHandlerMapping： 实现url->RequestMappingInfo->HandlerMethod的映射

具体实现：

1. SimpleUrlHandlerMapping：支持直接配置，调用父类注册
2. BeanNameUrlHandlerMapping：支持以 /beanName->beanName 的形式注册
3. ControllerBeanNameHandlerMapping：
4. ControllerClassNameHandlerMapping：
5. RequestMappingHandlerMapping：
6. DefaultAnnotationHandlerMapping：已经废弃

默认策略：

DispatcherServlet.properties 默认配置：BeanNameUrlHandlerMapping,DefaultAnnotationHandlerMapping
<mvc:annotation-driven/>配置：RequestMappingHandlerMapping，BeanNameUrlHandlerMapping

<mvc:default-servlet-handler/>配置：SimpleUrlHandlerMapping

<mvc:annotation-driven/>配置：SimpleUrlHandlerMapping（Controller接口）

<mvc:view-controller/> 配置： SimpleUrlHandlerMapping （ParameterizableViewController实现类）

DispatcherServlet初始化策略：

private void initHandlerMappings(ApplicationContext context) {
		this.handlerMappings = null;

		if (this.detectAllHandlerMappings) {
			// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
			Map<String, HandlerMapping> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerMappings = new ArrayList<HandlerMapping>(matchingBeans.values());
				// We keep HandlerMappings in sorted order.
				OrderComparator.sort(this.handlerMappings);
			}
		}
		else {
			try {
				HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
				this.handlerMappings = Collections.singletonList(hm);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Ignore, we'll add a default HandlerMapping later.
			}
		}

		// Ensure we have at least one HandlerMapping, by registering
		// a default HandlerMapping if no other mappings are found.
		if (this.handlerMappings == null) {
			this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
			if (logger.isDebugEnabled()) {
				logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
			}
		}
	}

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