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要想了解决Spring MVC是怎么把@RequestMapping注解了的方法以及类解析的，首先我们需要关注AbstractHandlerMethodMapping#afterPropertiesSet这个方法，而这个方法是Spring的init方法，是Spring在进行初始化bean之前在DI注入之后调用到的方法。所以当Spring容器初始化之后，@RequestMapping就会被解析成Spring容器的bean管理。通过这个方法的说明也能验证之前所说的。我们首先来关注一下@RequestMapping的时序图:

下面就入口方法。

/** * Detects handler methods at initialization. */public void afterPropertiesSet() {    initHandlerMethods();}

1、初始化处理client页面request的方法

下面我们就要重点关注AbstractHandlerMethodMapping#initHandlerMethods这个方法了。

/** * Scan beans in the ApplicationContext, detect and register handler methods. * @see #isHandler(Class) * @see #getMappingForMethod(Method, Class) * @see #handlerMethodsInitialized(Map) */protected void initHandlerMethods() {    if (logger.isDebugEnabled()) {        logger.debug("Looking for request mappings in application context: " + getApplicationContext());    }    // 读取Spring容器中的所有beanNames    String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?            BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :            getApplicationContext().getBeanNamesForType(Object.class));    // 遍历这些bean，检测出处理方法         for (String beanName : beanNames) {        // 判断这个bean是不是处理类(根据这个类是否使用了@Controller或@RequestMapping)        if (isHandler(getApplicationContext().getType(beanName))){            detectHandlerMethods(beanName);        }    }    // 处理方法后期处理,Spring空实现,方便以后扩展    handlerMethodsInitialized(getHandlerMethods());}

那么我们的关注点就需要放在detectHandlerMethods这个方法上了。

2、detectHandlerMethods

下面我们再来看一下AbstractHandlerMethodMapping#detectHandlerMethods这个方法。

protected void detectHandlerMethods(final Object handler) {    // 从Spring容器中获取这个类    Class
    handlerType =            (handler instanceof String ? getApplicationContext().getType((String) handler) : handler.getClass());    // Avoid repeated calls to getMappingForMethod which would rebuild RequestMatchingInfo instances    final Map
   
     mappings = new IdentityHashMap
    
     ();    final Class
      userType = ClassUtils.getUserClass(handlerType);    // 从处理类(@Controller)中获取处理方法(@RequestMapping)    Set
     
       methods = HandlerMethodSelector.selectMethods(userType, new MethodFilter() {        public boolean matches(Method method) {            T mapping = getMappingForMethod(method, userType);            if (mapping != null) {                mappings.put(method, mapping);                return true;            }            else {                return false;            }        }    });    // 注册方法,    for (Method method : methods) {        registerHandlerMethod(handler, method, mappings.get(method));    }}
     
    
   

3、getMappingForMethod

Spring MVC通过RequestMappingHandlerMapping#getMappingForMethod(Method method, Class

/** * Uses method and type-level @{
   @link RequestMapping} annotations to create * the RequestMappingInfo. * @return the created RequestMappingInfo, or {
   @code null} if the method * does not have a {
   @code @RequestMapping} annotation. * @see #getCustomMethodCondition(Method) * @see #getCustomTypeCondition(Class) */@Overrideprotected RequestMappingInfo getMappingForMethod(Method method, Class
    handlerType) {    RequestMappingInfo info = null;    // 这个方法是否使用@RequestMapping信息    RequestMapping methodAnnotation = AnnotationUtils.findAnnotation(method, RequestMapping.class);    if (methodAnnotation != null) {        // 空实现,方便以后扩展        RequestCondition
    methodCondition = getCustomMethodCondition(method);        // 创建RequestMappingInfo比较简单，如果感兴趣可以自己去看看        info = createRequestMappingInfo(methodAnnotation, methodCondition);        // 查询这个Controller上面使用@RequestMapping信息        RequestMapping typeAnnotation = AnnotationUtils.findAnnotation(handlerType, RequestMapping.class);        if (typeAnnotation != null) {            // 空实现,方便以后扩展            RequestCondition
    typeCondition = getCustomTypeCondition(handlerType);            // 把Class上面的@RequestMapping信息与方法上的@RequestMapping信息合并起来            info = createRequestMappingInfo(typeAnnotation, typeCondition).combine(info);        }    }    return info;}

返回info主要是包含@RequestMapping的标签信息,我们可以看看info中的信息：

4、registerHandlerMethod

然后我们就关注一下。第二步中的detectHandlerMethods方法中的registerHandlerMethod方法。

/** * Register a handler method and its unique mapping. * @param handler the bean name of the handler or the handler instance * @param method the method to register * @param mapping the mapping conditions associated with the handler method * @throws IllegalStateException if another method was already registered * under the same mapping */protected void registerHandlerMethod(Object handler, Method method, T mapping) {    HandlerMethod newHandlerMethod = createHandlerMethod(handler, method);    HandlerMethod oldHandlerMethod = this.handlerMethods.get(mapping);    if (oldHandlerMethod != null && !oldHandlerMethod.equals(newHandlerMethod)) {        throw new IllegalStateException("Ambiguous mapping found. Cannot map '" + newHandlerMethod.getBean() +                "' bean method \n" + newHandlerMethod + "\nto " + mapping + ": There is already '" +                oldHandlerMethod.getBean() + "' bean method\n" + oldHandlerMethod + " mapped.");    }    // 防止定义相同的处理映射    this.handlerMethods.put(mapping, newHandlerMethod);    if (logger.isInfoEnabled()) {        logger.info("Mapped \"" + mapping + "\" onto " + newHandlerMethod);    }    Set
   
     patterns = getMappingPathPatterns(mapping);    // 存在URL与RequestMappingInfo的映射    for (String pattern : patterns) {        if (!getPathMatcher().isPattern(pattern)) {            this.urlMap.add(pattern, mapping);        }    }}
   

现在我们来看看这个解析之后这个类之中属性。

当页面有url请求过来.首先通过urlMap查询RequestMappingInfo的信息，然后再通过handerMethods查询到HanderMethod的信息。这样url请求是不是与Controller中的方法结合了起来。具体是怎么调用的，可以看看我写的Blog –

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