1. 目录

[TOC]

2. 说明

请求映射器主要是将url映射成应用中的执行对象，一般我们项目中是通过RequestMappingHandlerMapping映射Controller

3. 依赖分析

4. 源码分析

从springmvc启动流程可以知道，springmvc请求映射是在initHandlerMappings()中初始化的

4.1. initHandlerMappings()

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

        //是否检测容器中的bean，默认为true
		if (this.detectAllHandlerMappings) {

            //这里从容器中获取HandlerMapping对应的bean，由于在容器加载spring-mvc.xml的时候默认设置了两个值（当配置<mvc:annotation-driven>的时候）
            //因此这里是可以拿到的，具体我们后面分析这部分是怎么来的
			Map<String, HandlerMapping> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerMappings = new ArrayList<>(matchingBeans.values());
                //排序，即@ProvityOrdered -> @Ordered -> 普通的 
				AnnotationAwareOrderComparator.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.
			}
		}
        //没有从容器中拿到handlerMapping，则取默认值，默认值是从DispatcherServlet.properties中加载的
        //DispatcherServlet的静态初始代码块中加载的，即加载类的时候就加入了HandlerMappings等
		if (this.handlerMappings == null) {
			this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
			if (logger.isTraceEnabled()) {
				logger.trace("No HandlerMappings declared for servlet '" + getServletName() +
						"': using default strategies from DispatcherServlet.properties");
			}
		}
	}

静态加载默认处理器

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static {
    //静态加载默认处理器
    try {
        ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
        defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
    }
    catch (IOException ex) {
        throw new IllegalStateException("Could not load '" + DEFAULT_STRATEGIES_PATH + "': " + ex.getMessage());
    }
}

4.2. 加载HandlerMapping 至容器中

前面启动流程我们已经讲了许多默认的bean的加载，这里再回顾一下RequestMappingHandlerMapping的加载

在初始化mvc上下问的时候解析加载beanDefinition的时候,spring在DefaultBeanDefinitionDocumentReader解析自定义节点的时候，会通过BeanDefinitionParserDelegate加载MvcNamespaceHandler作为NamespaceHandlerSupport解析xml节点。
NamespaceHandlerSupport配置的替换规则是在spring-mvc包下的META-INF/spring.handlers中(具体spring的beanDifinition加载中有解析)，
我们来看MvcNamespaceHandler代码

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@Override
public void init() {
    registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());
    registerBeanDefinitionParser("default-servlet-handler", new DefaultServletHandlerBeanDefinitionParser());
    registerBeanDefinitionParser("interceptors", new InterceptorsBeanDefinitionParser());
    registerBeanDefinitionParser("resources", new ResourcesBeanDefinitionParser());
    registerBeanDefinitionParser("view-controller", new ViewControllerBeanDefinitionParser());
    registerBeanDefinitionParser("redirect-view-controller", new ViewControllerBeanDefinitionParser());
    registerBeanDefinitionParser("status-controller", new ViewControllerBeanDefinitionParser());
    registerBeanDefinitionParser("view-resolvers", new ViewResolversBeanDefinitionParser());
    registerBeanDefinitionParser("tiles-configurer", new TilesConfigurerBeanDefinitionParser());
    registerBeanDefinitionParser("freemarker-configurer", new FreeMarkerConfigurerBeanDefinitionParser());
    registerBeanDefinitionParser("groovy-configurer", new GroovyMarkupConfigurerBeanDefinitionParser());
    registerBeanDefinitionParser("script-template-configurer", new ScriptTemplateConfigurerBeanDefinitionParser());
    registerBeanDefinitionParser("cors", new CorsBeanDefinitionParser());
}

初始化的时候默认加了一系列的BeanDefinitionParser解析器，其中就包括了AnnotationDrivenBeanDefinitionParser,这个Parser在执行解析的时候会将RequestMappingHandlerMapping注册到beanDifinitionMap中，代码如下：

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public BeanDefinition parse(Element element, ParserContext context) {
    Object source = context.extractSource(element);
    XmlReaderContext readerContext = context.getReaderContext();

    CompositeComponentDefinition compDefinition = new CompositeComponentDefinition(element.getTagName(), source);
    context.pushContainingComponent(compDefinition);

    RuntimeBeanReference contentNegotiationManager = getContentNegotiationManager(element, source, context);

    //加载RequestMappingHandlerMapping，并配置优先级，
    RootBeanDefinition handlerMappingDef = new RootBeanDefinition(RequestMappingHandlerMapping.class);
    handlerMappingDef.setSource(source);
    handlerMappingDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
    handlerMappingDef.getPropertyValues().add("order", 0);
    handlerMappingDef.getPropertyValues().add("contentNegotiationManager", contentNegotiationManager);

    if (element.hasAttribute("enable-matrix-variables")) {
        Boolean enableMatrixVariables = Boolean.valueOf(element.getAttribute("enable-matrix-variables"));
        handlerMappingDef.getPropertyValues().add("removeSemicolonContent", !enableMatrixVariables);
    }

    configurePathMatchingProperties(handlerMappingDef, element, context);
    //注册HandlerMappings
    readerContext.getRegistry().registerBeanDefinition(HANDLER_MAPPING_BEAN_NAME, handlerMappingDef);



    //顺便提一下和它相似的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);
    addRequestBodyAdvice(handlerAdapterDef);
    addResponseBodyAdvice(handlerAdapterDef);

    if (element.hasAttribute("ignore-default-model-on-redirect")) {
        Boolean ignoreDefaultModel = Boolean.valueOf(element.getAttribute("ignore-default-model-on-redirect"));
        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);
    readerContext.getRegistry().registerBeanDefinition(HANDLER_ADAPTER_BEAN_NAME, handlerAdapterDef);



    //这里注册组件，暂时不知道是干嘛用的，这个context也不是 spring上下文
    context.registerComponent(new BeanComponentDefinition(handlerMappingDef, HANDLER_MAPPING_BEAN_NAME));
    context.registerComponent(new BeanComponentDefinition(handlerAdapterDef, HANDLER_ADAPTER_BEAN_NAME));


    // Ensure BeanNameUrlHandlerMapping (SPR-8289) and default HandlerAdapters are not "turned off"
    MvcNamespaceUtils.registerDefaultComponents(context, source);

    context.popAndRegisterContainingComponent();

    return null;
}

5. 总结

6. 注意事项