Spring AbstractApplicationContext抽象類的refresh()方法--筆記

Spring中AbstractApplicationContext抽象類的refresh()方法是用來刷新Spring的應用上下文的。下面Spring的應用上下文我都叫作context

    @Override
    public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // Prepare this context for refreshing.
            prepareRefresh();//一 // Tell the subclass to refresh the internal bean factory.
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();//二、 // Prepare the bean factory for use in this context.
            prepareBeanFactory(beanFactory);//三、 try {
                // Allows post-processing of the bean factory in context subclasses.
                postProcessBeanFactory(beanFactory);//四、

                // Invoke factory processors registered as beans in the context.
                invokeBeanFactoryPostProcessors(beanFactory);//五、 // Register bean processors that intercept bean creation.
                registerBeanPostProcessors(beanFactory);//六、 // Initialize message source for this context.
                initMessageSource();//七、 // Initialize event multicaster for this context.
                initApplicationEventMulticaster();//八、 // Initialize other special beans in specific context subclasses.
                onRefresh();//九、 // Check for listener beans and register them.
                registerListeners();//十、 // Instantiate all remaining (non-lazy-init) singletons.
                finishBeanFactoryInitialization(beanFactory);//十一、 // Last step: publish corresponding event.
                finishRefresh();//十二、
            }

            catch (BeansException ex) {
                if (logger.isWarnEnabled()) {
                    logger.warn("Exception encountered during context initialization - " +
                            "cancelling refresh attempt: " + ex);
                }

                // Destroy already created singletons to avoid dangling resources.
                destroyBeans();//如果刷新失敗那么就會將已經創建好的單例Bean銷毀掉 // Reset 'active' flag.
                cancelRefresh(ex);//重置context的活動狀態 // Propagate exception to caller.
                throw ex;//拋出異常
            }

            finally {
                // Reset common introspection caches in Spring's core, since we
                // might not ever need metadata for singleton beans anymore...
                resetCommonCaches();//重置的Spring內核的緩存。因為可能不再需要metadata給單例Bean了。
            }
        }
    }

這個方法的每一行代碼都很重要。已經在代碼中標上序號，下面會一句一句來解釋。

一、prePareRefresh()

　　①、這個方法設置context的啟動日期。

　　②、設置context當前的狀態，是活動狀態還是關閉狀態。

　　③、初始化context environment（上下文環境）中的占位符屬性來源。

　　④、驗證所有必需的屬性。

二、ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

　　讓這個類（AbstractApplicationContext）的子類刷新內部bean工廠。實際上就是重新創建一個bean工廠。

obtainFreshBeanFactory()方法的代碼如下：

    /**
     * Tell the subclass to refresh the internal bean factory.
     * @return the fresh BeanFactory instance
     * @see #refreshBeanFactory()
     * @see #getBeanFactory()
     */
    protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        refreshBeanFactory();//真正的刷新bean工廠。
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        if (logger.isDebugEnabled()) {
            logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
        }
        return beanFactory;
    }

上述代碼中標紅的refreshBeanFactory()最重要，其具體代碼如下：

    /**
     * This implementation performs an actual refresh of this context's underlying
     * bean factory, shutting down the previous bean factory (if any) and
     * initializing a fresh bean factory for the next phase of the context's lifecycle.
     */
    @Override
    protected final void refreshBeanFactory() throws BeansException {
        if (hasBeanFactory()) {//如果已經存在一個bean工廠那么就將其銷毀，關閉。
            destroyBeans();
            closeBeanFactory();
        }
        try {
            DefaultListableBeanFactory beanFactory = createBeanFactory();//新建一個Bean工廠。
            beanFactory.setSerializationId(getId());
            customizeBeanFactory(beanFactory);//自定義bean工廠。
            loadBeanDefinitions(beanFactory);//加載BeanDefinition synchronized (this.beanFactoryMonitor) {
                this.beanFactory = beanFactory;//將創建好的bean工廠的引用交給的context來管理。
            }
        }
        catch (IOException ex) {//加載bean定義資源的時候可能會拋出異常。 throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
        }
    }

三、prepareBeanFactory(beanFactory);

上一步已經把工廠建好了，但是還不能投入使用，因為工廠里什么都沒有，還需要配置一些東西。看看這個方法的注釋

他說配置這個工廠的標准環境，比如context的類加載器和后處理器。看看具體有哪些，反正很多。都是往BeanFactory中add什么東西，或者Register什么東西。反正在一系列的add和Register后工廠的功能會越來越健全。

直接貼代碼：prepareBeanFactory(ConfigurableListableBeanFactory beanFactory)

    /**
     * Configure the factory's standard context characteristics,
     * such as the context's ClassLoader and post-processors.
     * @param beanFactory the BeanFactory to configure
     */
    protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        // Tell the internal bean factory to use the context's class loader etc.
        beanFactory.setBeanClassLoader(getClassLoader());
        beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
        beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

        // Configure the bean factory with context callbacks.
        beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
        beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
        beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
        beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
        beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

        // BeanFactory interface not registered as resolvable type in a plain factory.
        // MessageSource registered (and found for autowiring) as a bean.
        beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
        beanFactory.registerResolvableDependency(ResourceLoader.class, this);
        beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
        beanFactory.registerResolvableDependency(ApplicationContext.class, this);

        // Register early post-processor for detecting inner beans as ApplicationListeners.
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

        // Detect a LoadTimeWeaver and prepare for weaving, if found.
        if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            // Set a temporary ClassLoader for type matching.
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }

        // Register default environment beans.
        if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
            beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
        }
        if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
        }
        if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
        }
    }

 

四、postProcessBeanFactory(beanFactory);

上面對bean工廠進行了許多配置，現在需要對bean工廠進行一些處理。

　　①、添加一個ServletContextAwareProcessor到bean工廠中。

　　②、在bean工廠自動裝配的時候忽略一些接口。如：ServletContextAware、ServletConfigAware

　　③、注冊WEB應用特定的域（scope）到bean工廠中，以便WebApplicationContext可以使用它們。比如"request", "session", "globalSession", "application"，

　　④、注冊WEB應用特定的Environment bean到bean工廠中，以便WebApplicationContext可以使用它們。如："contextParameters", "contextAttributes"

下面是這個方法的代碼：

/**
     * Register request/session scopes, a {@link ServletContextAwareProcessor}, etc.
     */
    @Override
    protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext, this.servletConfig));
        beanFactory.ignoreDependencyInterface(ServletContextAware.class);
        beanFactory.ignoreDependencyInterface(ServletConfigAware.class);

        WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext);
        WebApplicationContextUtils.registerEnvironmentBeans(beanFactory, this.servletContext, this.servletConfig);
    }

 

 五、invokeBeanFactoryPostProcessors(beanFactory)

這一步也是對bean工廠進行一些處理。這一步主要是調用所有的bean工廠處理器（BeanFactoryPostProcessor）對bean工廠進行一些處理。這個方法必須在所有的singleton初始化之前調用。

    /**
     * Instantiate and invoke all registered BeanFactoryPostProcessor beans,
     * respecting explicit order if given.
     * <p>Must be called before singleton instantiation.
     */
    protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());//這個行代碼重要 // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
        // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
        if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }
    }

上面標紅的代碼的具體實現如下，代碼非常多。主要是在這里面調用了所有的BeanFactoryPostProcessor。

    public static void invokeBeanFactoryPostProcessors(
            ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {

        // Invoke BeanDefinitionRegistryPostProcessors first, if any.
        Set<String> processedBeans = new HashSet<String>();

        if (beanFactory instanceof BeanDefinitionRegistry) {
            BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
            List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
            List<BeanDefinitionRegistryPostProcessor> registryPostProcessors =
                    new LinkedList<BeanDefinitionRegistryPostProcessor>();

            for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
                if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                    BeanDefinitionRegistryPostProcessor registryPostProcessor =
                            (BeanDefinitionRegistryPostProcessor) postProcessor;
                    registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
                    registryPostProcessors.add(registryPostProcessor);
                }
                else {
                    regularPostProcessors.add(postProcessor);
                }
            }

            // Do not initialize FactoryBeans here: We need to leave all regular beans
            // uninitialized to let the bean factory post-processors apply to them!
            // Separate between BeanDefinitionRegistryPostProcessors that implement
            // PriorityOrdered, Ordered, and the rest.
            String[] postProcessorNames =
                    beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);

            // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
            List<BeanDefinitionRegistryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
            for (String ppName : postProcessorNames) {
                if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                    priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                }
            }
            sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
            registryPostProcessors.addAll(priorityOrderedPostProcessors);
            invokeBeanDefinitionRegistryPostProcessors(priorityOrderedPostProcessors, registry);

            // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
            postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            List<BeanDefinitionRegistryPostProcessor> orderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
            for (String ppName : postProcessorNames) {
                if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
                    orderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                }
            }
            sortPostProcessors(beanFactory, orderedPostProcessors);
            registryPostProcessors.addAll(orderedPostProcessors);
            invokeBeanDefinitionRegistryPostProcessors(orderedPostProcessors, registry);

            // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
            boolean reiterate = true;
            while (reiterate) {
                reiterate = false;
                postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
                for (String ppName : postProcessorNames) {
                    if (!processedBeans.contains(ppName)) {
                        BeanDefinitionRegistryPostProcessor pp = beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class);
                        registryPostProcessors.add(pp);
                        processedBeans.add(ppName);
                        pp.postProcessBeanDefinitionRegistry(registry);
                        reiterate = true;
                    }
                }
            }

            // Now, invoke the postProcessBeanFactory callback of all processors handled so far.
            invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);
            invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
        }

        else {
            // Invoke factory processors registered with the context instance.
            invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
        }

        // Do not initialize FactoryBeans here: We need to leave all regular beans
        // uninitialized to let the bean factory post-processors apply to them!
        String[] postProcessorNames =
                beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

        // Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
        // Ordered, and the rest.
        List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
        List<String> orderedPostProcessorNames = new ArrayList<String>();
        List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
        for (String ppName : postProcessorNames) {
            if (processedBeans.contains(ppName)) {
                // skip - already processed in first phase above
            }
            else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
            }
            else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessorNames.add(ppName);
            }
            else {
                nonOrderedPostProcessorNames.add(ppName);
            }
        }

        // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
        sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
        invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

        // Next, invoke the BeanFactoryPostProcessors that implement Ordered.
        List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
        for (String postProcessorName : orderedPostProcessorNames) {
            orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }
        sortPostProcessors(beanFactory, orderedPostProcessors);
        invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

        // Finally, invoke all other BeanFactoryPostProcessors.
        List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
        for (String postProcessorName : nonOrderedPostProcessorNames) {
            nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }
        invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

        // Clear cached merged bean definitions since the post-processors might have
        // modified the original metadata, e.g. replacing placeholders in values...
        beanFactory.clearMetadataCache();
    }

 

六、registerBeanPostProcessors(beanFactory);

注冊用來攔截bean創建的BeanPostProcessor bean.這個方法需要在所有的application bean初始化之前調用。把這個注冊的任務委托給了PostProcessorRegistrationDelegate來完成。

    public static void registerBeanPostProcessors(
            ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

        String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

        // Register BeanPostProcessorChecker that logs an info message when
        // a bean is created during BeanPostProcessor instantiation, i.e. when
        // a bean is not eligible for getting processed by all BeanPostProcessors.
        int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
        beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

        // Separate between BeanPostProcessors that implement PriorityOrdered,
        // Ordered, and the rest.
        List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
        List<BeanPostProcessor> internalPostProcessors = new ArrayList<BeanPostProcessor>();
        List<String> orderedPostProcessorNames = new ArrayList<String>();
        List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
        for (String ppName : postProcessorNames) {
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
                priorityOrderedPostProcessors.add(pp);
                if (pp instanceof MergedBeanDefinitionPostProcessor) {
                    internalPostProcessors.add(pp);
                }
            }
            else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessorNames.add(ppName);
            }
            else {
                nonOrderedPostProcessorNames.add(ppName);
            }
        }

        // First, register the BeanPostProcessors that implement PriorityOrdered.首先，注冊實現了PriorityOrdered接口的BeanPostProcessor
        sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
        registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

        // Next, register the BeanPostProcessors that implement Ordered.然后注冊實現了Ordered接口的BeanPostProcessor
        List<BeanPostProcessor> orderedPostProcessors = new ArrayList<BeanPostProcessor>();
        for (String ppName : orderedPostProcessorNames) {
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            orderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        sortPostProcessors(beanFactory, orderedPostProcessors);
        registerBeanPostProcessors(beanFactory, orderedPostProcessors);

        // Now, register all regular BeanPostProcessors.注冊所有常規的的BeanPostProcessor
        List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
        for (String ppName : nonOrderedPostProcessorNames) {
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            nonOrderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

        // Finally, re-register all internal BeanPostProcessors.最后重新注冊所有的內部BeanPostProcessor
        sortPostProcessors(beanFactory, internalPostProcessors);
        registerBeanPostProcessors(beanFactory, internalPostProcessors);

        // Re-register post-processor for detecting inner beans as ApplicationListeners,重新注冊用來自動探測內部ApplicationListener的post-processor，這樣可以將他們移到處理器鏈條的末尾。 // moving it to the end of the processor chain (for picking up proxies etc).
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
    }

七、initMessageSource();

初始化MessageSource接口的一個實現類。這個接口提供了消息處理功能。主要用於國際化/i18n。

八、initApplicationEventMulticaster();

為這個context初始化一個事件廣播器（ApplicationEventMulticaster）。

AbstractApplicationContext中有一個常量：

    /**
     * Name of the ApplicationEventMulticaster bean in the factory.
     * If none is supplied, a default SimpleApplicationEventMulticaster is used.
     * @see org.springframework.context.event.ApplicationEventMulticaster
     * @see org.springframework.context.event.SimpleApplicationEventMulticaster
     */
    public static final String APPLICATION_EVENT_MULTICASTER_BEAN_NAME = "applicationEventMulticaster";

這個常量就是的ApplicationEventMulticaster bean的名字。程序首先會檢查bean工廠中是否有bean的名字和這個常量相同的，如果沒有則說明沒有那么就使用默認的ApplicationEventMulticaster 的實現：SimpleApplicationEventMulticaster

    /**
     * Initialize the ApplicationEventMulticaster.
     * Uses SimpleApplicationEventMulticaster if none defined in the context.
     * @see org.springframework.context.event.SimpleApplicationEventMulticaster
     */
    protected void initApplicationEventMulticaster() {
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {檢查是否給context配了一個ApplicationEventMulticaster實現類 this.applicationEventMulticaster =
                    beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
            if (logger.isDebugEnabled()) {
                logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
            }
        }
        else {//如果沒有，就是用默認的實現類 SimpleApplicationEventMulticaster this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
            beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
            if (logger.isDebugEnabled()) {
                logger.debug("Unable to locate ApplicationEventMulticaster with name '" +
                        APPLICATION_EVENT_MULTICASTER_BEAN_NAME +
                        "': using default [" + this.applicationEventMulticaster + "]");
            }
        }
    }

九、onRefresh();

在AbstractApplicationContext的子類中初始化其他特殊的bean。其實就是初始化ThemeSource接口的實例。這個方法需要在所有單例bean初始化之前調用。

十、registerListeners();

注冊應用的監聽器。就是注冊實現了ApplicationListener接口的監聽器bean，這些監聽器是注冊到ApplicationEventMulticaster中的。這不會影響到其它監聽器bean。在注冊完以后，還會將其前期的事件發布給相匹配的監聽器。

    /**
     * Add beans that implement ApplicationListener as listeners.
     * Doesn't affect other listeners, which can be added without being beans.
     */
    protected void registerListeners() {
        // Register statically specified listeners first.
        for (ApplicationListener<?> listener : getApplicationListeners()) {
            getApplicationEventMulticaster().addApplicationListener(listener);
        }

        // Do not initialize FactoryBeans here: We need to leave all regular beans
        // uninitialized to let post-processors apply to them!
        String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
        for (String listenerBeanName : listenerBeanNames) {
            getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
        }

        // Publish early application events now that we finally have a multicaster...至此，已經完成將監聽器注冊到ApplicationEventMulticaster中，下面將發布前期的事件給監聽器。
        Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
        this.earlyApplicationEvents = null;
        if (earlyEventsToProcess != null) {
            for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
                getApplicationEventMulticaster().multicastEvent(earlyEvent);
            }
        }
    }

十一、finishBeanFactoryInitialization(beanFactory);

完成bean工廠的初始化工作。這一步非常復雜，也非常重要，涉及到了bean的創建。第二步中只是完成了BeanDefinition的定義、解析、處理、注冊。但是還沒有初始化bean實例。這一步將初始化所有非懶加載的單例bean。這一步將會重新在一篇新的筆記中介紹。

十二、finishRefresh();

完成context的刷新。主要是調用LifecycleProcessor的onRefresh()方法，並且發布事件（ContextRefreshedEvent）。