Spring MVC中HandlerMapping的初始化

        HandlerMapping的初始化发生在核心类：AbstractHandlerMethodMapping中，该类实现了InitializingBean，且RequestMappingHandlerMapping为该类子类，spring启动过程中会通过回调afterPropertiesSet方法完成HandlerMethod的初始化。

        初始化的过程实际上是将Controller中的方法注册到MappingRegistry中，MappingRegistry为AbstractHandlerMethodMapping的内部类，用于存放@RequestMapping中定义的URL路径(抽象为RequestMappingInfo)与对应Controller方法(抽象为HandlerMethod)的映射关系。注册过程源码解析如下。

        HandlerMethod的初始化：

	@Override
	public void afterPropertiesSet() {
		initHandlerMethods();
	}

        扫描ApplicationContext中所有的bean，找到handler methods并注册：

	protected void initHandlerMethods() {
		if (logger.isDebugEnabled()) {
			logger.debug("Looking for request mappings in application context: " + getApplicationContext());
		}
        //获取spring容器中所有的beanNames
		String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?
				BeanFactoryUtils.beanNamesForTypeIncludingAncestors(obtainApplicationContext(), Object.class) :
				obtainApplicationContext().getBeanNamesForType(Object.class));

		for (String beanName : beanNames) {
            //排除以scopedTarget.开头的bean
			if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
				Class<?> beanType = null;
				try {
                    //获取beanName对应的类型
					beanType = obtainApplicationContext().getType(beanName);
				}
				catch (Throwable ex) {
					// An unresolvable bean type, probably from a lazy bean - let's ignore it.
					if (logger.isDebugEnabled()) {
						logger.debug("Could not resolve target class for bean with name '" + beanName + "'", ex);
					}
				}
                //isHandler()检测是否是handler，
                //模版方法RequestMappingHandlerMapping.isHandler() 
                //判断是否是@controller 或者 @RequestMapping
				if (beanType != null && isHandler(beanType)) {
                    //查找HandlerMethods并注册
					detectHandlerMethods(beanName);
				}
			}
		}
        //改方法方法体为空，RequestMappingHandlerMapping也没有扩展改方法
		handlerMethodsInitialized(getHandlerMethods());
	}

        查找并注册当前Handler中的Mehods：

	protected void detectHandlerMethods(final Object handler) {
        //获取当前Handler的类型
		Class<?> handlerType = (handler instanceof String ?
				obtainApplicationContext().getType((String) handler) : handler.getClass());

		if (handlerType != null) {
            //针对CGLIB生成的子类，找到真正用户定义的类型userType
			final Class<?> userType = ClassUtils.getUserClass(handlerType);
            //从Class中获取<Method，RequestMappingInfo>
			Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
					(MethodIntrospector.MetadataLookup<T>) method -> {
						try {
							return getMappingForMethod(method, userType);
						}
						catch (Throwable ex) {
							throw new IllegalStateException("Invalid mapping on handler class [" +
									userType.getName() + "]: " + method, ex);
						}
					});
			if (logger.isDebugEnabled()) {
				logger.debug(methods.size() + " request handler methods found on " + userType + ": " + methods);
			}
			for (Map.Entry<Method, T> entry : methods.entrySet()) {
                //判断Method是否可调用（不是private方法）
				Method invocableMethod = AopUtils.selectInvocableMethod(entry.getKey(), userType);
                //RequestMappingInfo（方法上的信息）
				T mapping = entry.getValue();
                //将Handler，Method，RequestMappingInfo注册到MappingRegistry中
				registerHandlerMethod(handler, invocableMethod, mapping);
			}
		}
	}