对Spring框架中refresh()的源码分析

public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
        // Prepare this context for refreshing.
        prepareRefresh();

        // Tell the subclass to refresh the internal bean factory.
        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

        // Prepare the bean factory for use in this context.
        prepareBeanFactory(beanFactory);

        try {
            // Allows post-processing of the bean factory in context subclasses.
            postProcessBeanFactory(beanFactory);

            // Invoke factory processors registered as beans in the context.
            invokeBeanFactoryPostProcessors(beanFactory);

            // Register bean processors that intercept bean creation.
            registerBeanPostProcessors(beanFactory);

            // Initialize message source for this context.
            initMessageSource();

            // Initialize event multicaster for this context.
            initApplicationEventMulticaster();

            // Initialize other special beans in specific context subclasses.
            onRefresh();

            // Check for listener beans and register them.
            registerListeners();

            // Instantiate all remaining (non-lazy-init) singletons.
            // spring开始实例化单例的类
            finishBeanFactoryInitialization(beanFactory);

            // Last step: publish corresponding event.
            finishRefresh();
        }

        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();

            // Reset 'active' flag.
            cancelRefresh(ex);

            // Propagate exception to caller.
            throw ex;
        }

        finally {
            // Reset common introspection caches in Spring's core, since we
            // might not ever need metadata for singleton beans anymore...
            resetCommonCaches();
        }
    }
}

prepareRefresh()

refresh前的预处理

/**
  * Prepare this context for refreshing, setting its startup date and
  * active flag as well as performing any initialization of property sources.
  */
protected void prepareRefresh() {
    // Switch to active.
    this.startupDate = System.currentTimeMillis();
    this.closed.set(false);
    this.active.set(true);

    if (logger.isDebugEnabled()) {
        if (logger.isTraceEnabled()) {
            logger.trace("Refreshing " + this);
        }
        else {
            logger.debug("Refreshing " + getDisplayName());
        }
    }

    // Initialize any placeholder property sources in the context environment.
    initPropertySources();

    // Validate that all properties marked as required are resolvable:
    // see ConfigurablePropertyResolver#setRequiredProperties
    getEnvironment().validateRequiredProperties();

    // Store pre-refresh ApplicationListeners...
    if (this.earlyApplicationListeners == null) {
        this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
    }
    else {
        // Reset local application listeners to pre-refresh state.
        this.applicationListeners.clear();
        this.applicationListeners.addAll(this.earlyApplicationListeners);
    }

    // Allow for the collection of early ApplicationEvents,
    // to be published once the multicaster is available...
    this.earlyApplicationEvents = new LinkedHashSet<>();
}

• initPropertySources() 初始化一些属性设置；子类自定义个性化的属性设置方法；
• getEnvironment().validateRequireProperties() 检验属性的合法等；
• earlyApplicationEvents = new LinkedHashSet<>(); 保存容器中的一些早期事件；

obtainFreshBeanFactory()

// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
    refreshBeanFactory();
    return getBeanFactory();
}

refreshBeanFactory()

刷新(创建)BeanFactory

public GenericApplicationContext() {
    this.beanFactory = new DefaultListableBeanFactory();
}

/**
  * Do nothing: We hold a single internal BeanFactory and rely on callers
  * to register beans through our public methods (or the BeanFactory's).
  * @see #registerBeanDefinition
  */
@Override
protected final void refreshBeanFactory() throws IllegalStateException {
    if (!this.refreshed.compareAndSet(false, true)) {
        throw new IllegalStateException(
            "GenericApplicationContext does not support multiple refresh attempts: just call 'refresh' once");
    }
    // 设置id
    this.beanFactory.setSerializationId(getId());
}

getBeanFactory()

返回刚才GenericApplicationContext创建的BeanFactory对象；

/**
  * Return the single internal BeanFactory held by this context
  * (as ConfigurableListableBeanFactory).
  */
@Override
public final ConfigurableListableBeanFactory getBeanFactory() {
    return this.beanFactory;
}

prepareBeanFactory(beanFactory)

BeanFactory的预准备工作（BeanFactory的一些设置）

/**
  * 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.
    // 1. 设置BeanFactory的类加载器、支持表达式解析器等
    beanFactory.setBeanClassLoader(getClassLoader());
    beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
    beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

    // Configure the bean factory with context callbacks.
    // 2. 添加部分BeanPostProcessor【ApplicationContextAwareProcessor】
    beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
    // 3. 设置忽略的自动装配的接口 
    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.
    // 4. 注册可以解析的自动装配（直接在任何组件中自动注入）
    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.
    // 5. 添加BeanPostProcessor【ApplicationListenerDetector】
    beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

    // Detect a LoadTimeWeaver and prepare for weaving, if found.
     // 6. 添加编译时的AspectJ
    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.
    // 7. 给BeanFactory注册一些能用的组件
    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());
    }
}

postProcessBeanFactory(beanFactory)

BeanFactory准备工作完成后进行的后置处理工作；

子类通过重写这个方法在BeanFactory创建并预准备完成以后做进一步的设置；

以上是BeanFactory的创建及预准备工作

---

invokeBeanFactoryPostProcessors(beanFactory)

执行BeanFactoryPostProcessor

BeanFactoryPostProcessor：BeanFactory的后置处理器，在BeanFactory标准初始化之后执行；

/**
  * Instantiate and invoke all registered BeanFactoryPostProcessor beans,
  * respecting explicit order if given.
  * <p>Must be called before singleton instantiation.
  */
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
 // 分析
    PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

    // 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()));
    }
}

PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors

两个接口：BeanFactoryPostProcessor，BeanDefinitionRegistryPostProcessor；

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

    // Invoke BeanDefinitionRegistryPostProcessors first, if any.
    Set<String> processedBeans = new HashSet<>();
    // BeanDefinitionRegistryPostProcessor 先对 BeanDefinitionRegistry 执行
    if (beanFactory instanceof BeanDefinitionRegistry) {
        BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
        List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
        List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();

        for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
            if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                BeanDefinitionRegistryPostProcessor registryProcessor =
                    (BeanDefinitionRegistryPostProcessor) postProcessor;
                registryProcessor.postProcessBeanDefinitionRegistry(registry);
                registryProcessors.add(registryProcessor);
            }
            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.
        List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

        // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
        String[] postProcessorNames =
            beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
        for (String ppName : postProcessorNames) {
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                processedBeans.add(ppName);
            }
        }
        sortPostProcessors(currentRegistryProcessors, beanFactory);
        registryProcessors.addAll(currentRegistryProcessors);
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        currentRegistryProcessors.clear();

        // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
        postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
        for (String ppName : postProcessorNames) {
            if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
                currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                processedBeans.add(ppName);
            }
        }
        sortPostProcessors(currentRegistryProcessors, beanFactory);
        registryProcessors.addAll(currentRegistryProcessors);
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        currentRegistryProcessors.clear();

        // 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)) {
                    currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                    reiterate = true;
                }
            }
            sortPostProcessors(currentRegistryProcessors, beanFactory);
            registryProcessors.addAll(currentRegistryProcessors);
            invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
            currentRegistryProcessors.clear();
        }

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

• 先执行BeanDefinitionRegistryPostProcessor：

  1. 获取所有的BeanDefinitionRegistryPostProcessor；

  2. 先执行实现了PriorityOrdered优先级接口的BeanDefinitionRegistryPostProcessor;

     postProcessor.postProcessBeanDefinitionRegistry(registry);

  3. 再执行实现了Ordered顺序接口的BeanDefinitionRegistryPostProcessor;

     postProcessor.postProcessBeanDefinitionRegistry(registry);

  4. 最后执行没有实现任何优先级或顺序接口的BeanDefinitionRegistryPostProcessor

     postProcessor.postProcessBeanDefinitionRegistry(registry);

• 再执行beanFactoryPostProcessor的方法：

  1. 获取所有的BeanFactoryPostProcessor；

  2. 先执行实现了PriorityOrdered优先级接口的BeanFactoryPostProcessor

     postProcessor.postProcessBeanFactory(beanFactory);

  3. 再执行实现了Ordered顺序接口的BeanFactoryPostProcessor

     postProcessor.postProcessBeanFactory(beanFactory);

  4. 最后执行没有实现任何优先级或顺序接口的BeanFactoryPostProcessor

     postProcessor.postProcessBeanFactory(beanFactory);

registerBeanPostProcessors(beanFactory)

注册BeanPostProcessor【Bean的后置处理器，拦截bean的创建过程】

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<>();
    List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
    List<String> orderedPostProcessorNames = new ArrayList<>();
    List<String> nonOrderedPostProcessorNames = new ArrayList<>();
    // 1.获取所有的BeanPostProcessor (后置处理器都可以通过PriorityOrdered、Ordered接口来执行优先级)
    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.
    // 2.先注册PriorityOrdered优先级接口的BeanPostProcessor, 把每一个BeanPostProcessor添加到Beanfactory中
    sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

    // Next, register the BeanPostProcessors that implement Ordered.
    // 3.再注册实现Ordered接口的
    List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
    for (String ppName : orderedPostProcessorNames) {
        BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
        orderedPostProcessors.add(pp);
        if (pp instanceof MergedBeanDefinitionPostProcessor) {
            internalPostProcessors.add(pp);
        }
    }
    sortPostProcessors(orderedPostProcessors, beanFactory);
    registerBeanPostProcessors(beanFactory, orderedPostProcessors);

    // Now, register all regular BeanPostProcessors.
    // 4.最后注册没有实现任何优先级接口的
    List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
    for (String ppName : nonOrderedPostProcessorNames) {
        BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
        nonOrderedPostProcessors.add(pp);
        // 对MergedBeanDefinitionPostProcessor进行判断
        if (pp instanceof MergedBeanDefinitionPostProcessor) {
            internalPostProcessors.add(pp);
        }
    }
    registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

    // Finally, re-register all internal BeanPostProcessors.
    // 5.最终注册MergedBeanDefinitionPostProcessor
    sortPostProcessors(internalPostProcessors, beanFactory);
    registerBeanPostProcessors(beanFactory, internalPostProcessors);

    // Re-register post-processor for detecting inner beans as ApplicationListeners,
    // moving it to the end of the processor chain (for picking up proxies etc).
    // 6.注册一个ApplicationListenerDetector，在Bean创建完成后检查是否是ApplicationListener，如果是，则applicationContext.addApplicationListener((ApplicationListener<?>) bean);
    beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}

/**
  * Register the given BeanPostProcessor beans.
  */
private static void registerBeanPostProcessors(
    ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {
    for (BeanPostProcessor postProcessor : postProcessors) {
        beanFactory.addBeanPostProcessor(postProcessor);
    }
}

不同接口类型的BeanPostProcessor在Bean创建前后的执行时机是不一样的：

BeanPostProcessor

InstantiationAwareBeanPostProcessor

DestructionAwareBeanPostProcessor

SmartInstantiationAwareBeanPostProcessor

MergedBeanDefinitionPostProcessor【internalPostProcessors】

initMessageSource()

初始化MessageSource组件（做国际化功能，消息绑定，消息解析）

/**
  * Initialize the MessageSource.
  * Use parent's if none defined in this context.
  */
protected void initMessageSource() {
    // 1.获取BeanFactory
    ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    // 2.判断容器中是否有id为messageSource，类型为MessageSource的组件, 若有则赋值给messageSource, 若没有则new DelegatingMessageSource(); 
    // MessageSource：取出国际化配置文件中的某个key值 (能按照区域信息获取)
    if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
        this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
        // Make MessageSource aware of parent MessageSource.
        if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
            HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
            if (hms.getParentMessageSource() == null) {
                // Only set parent context as parent MessageSource if no parent MessageSource
                // registered already.
                hms.setParentMessageSource(getInternalParentMessageSource());
            }
        }
        if (logger.isTraceEnabled()) {
            logger.trace("Using MessageSource [" + this.messageSource + "]");
        }
    }
    else {
        // Use empty MessageSource to be able to accept getMessage calls.
        DelegatingMessageSource dms = new DelegatingMessageSource();
        dms.setParentMessageSource(getInternalParentMessageSource());
        this.messageSource = dms;
        // 3.把创建好的MessageSource注册在容器中, 以后获取国际化配置文件的值时, 可以自动注入MessageSource, 例如 MessageSource.getMessage(String code, @Nullable Object[] args, Locale locale)
        beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
        if (logger.isTraceEnabled()) {
            logger.trace("No '" + MESSAGE_SOURCE_BEAN_NAME + "' bean, using [" + this.messageSource + "]");
        }
    }
}

initApplicationEventMulticaster()

初始化事件派发器

/**
  * Initialize the ApplicationEventMulticaster.
  * Uses SimpleApplicationEventMulticaster if none defined in the context.
  * @see org.springframework.context.event.SimpleApplicationEventMulticaster
  */
protected void initApplicationEventMulticaster() {
    // 1.获取BeanFactory
    ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    // 2.从BeanFactory中获取applicationEventMulticaster的ApplicationEventMulticaster
    if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
        this.applicationEventMulticaster =
            beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
        if (logger.isTraceEnabled()) {
            logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
        }
    }
    // 3.如果第二步中不存在, 则创建 new SimpleApplicationEventMulticaster(beanFactory);
    else {
        this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
        // 4.将创建的ApplicationEventMulticaster添加到BeanFactory中，以后其他组件直接自动注入
        beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
        if (logger.isTraceEnabled()) {
            logger.trace("No '" + APPLICATION_EVENT_MULTICASTER_BEAN_NAME + "' bean, using " +
                         "[" + this.applicationEventMulticaster.getClass().getSimpleName() + "]");
        }
    }
}

onRefresh()

留给子容器（子类）实现，子类重写这个方法，在容器刷新时可以自定义逻辑；

registerListeners()

将容器中所有项目里面的ApplicationListener注册进来

/**
  * 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.
    // 1.从容器中拿到所有的ApplicationListener
    for (ApplicationListener<?> listener : getApplicationListeners()) {
        // 2.将每个监听器添加到事件派发器中
        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...
    // 3.派发之前步骤产生的事件
    Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
    this.earlyApplicationEvents = null;
    if (!CollectionUtils.isEmpty(earlyEventsToProcess)) {
        for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
            getApplicationEventMulticaster().multicastEvent(earlyEvent);
        }
    }
}

finishBeanFactoryInitialization(beanFactory)

初始化所有剩下的单实例bean

/**
  * Finish the initialization of this context's bean factory,
  * initializing all remaining singleton beans.
  */
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
    // Initialize conversion service for this context.
    if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
        beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
        beanFactory.setConversionService(
            beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
    }

    // Register a default embedded value resolver if no bean post-processor
    // (such as a PropertyPlaceholderConfigurer bean) registered any before:
    // at this point, primarily for resolution in annotation attribute values.
    if (!beanFactory.hasEmbeddedValueResolver()) {
        beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
    }

    // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
    // 2.获取Bean的定义信息：RootBeanDefinition
    String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
    for (String weaverAwareName : weaverAwareNames) {
        getBean(weaverAwareName);
    }

    // Stop using the temporary ClassLoader for type matching.
    beanFactory.setTempClassLoader(null);

    // Allow for caching all bean definition metadata, not expecting further changes.
    beanFactory.freezeConfiguration();

    // Instantiate all remaining (non-lazy-init) singletons.
    // 实例化所有的单例，非lazy
    // 分析
    beanFactory.preInstantiateSingletons();
}

beanFactory.preInstantiateSingletons()

public void preInstantiateSingletons() throws BeansException {
    if (logger.isTraceEnabled()) {
        logger.trace("Pre-instantiating singletons in " + this);
    }

    // Iterate over a copy to allow for init methods which in turn register new bean definitions.
    // While this may not be part of the regular factory bootstrap, it does otherwise work fine.
    List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

    // Trigger initialization of all non-lazy singleton beans...
    // 1.获取容器中的所有Bean，依次进行初始化和创建对象
    // 根据名字遍历所有的BeanDefinition，继而验证BeanDefinition
    for (String beanName : beanNames) {
        // 2.获取Bean的定义信息：RootBeanDefinition
        RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
        // 3.Bean不是抽象的, 是单实例的, 不是懒加载的
        if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
            // 3.1 判断是否是FactoryBean：是否是实现FactoryBean接口的Bean；
            if (isFactoryBean(beanName)) {
                Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
                if (bean instanceof FactoryBean) {
                    FactoryBean<?> factory = (FactoryBean<?>) bean;
                    boolean isEagerInit;
                    if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                        isEagerInit = AccessController.doPrivileged(
                            (PrivilegedAction<Boolean>) ((SmartFactoryBean<?>) factory)::isEagerInit,
                            getAccessControlContext());
                    }
                    else {
                        isEagerInit = (factory instanceof SmartFactoryBean &&
                                       ((SmartFactoryBean<?>) factory).isEagerInit());
                    }
                    if (isEagerInit) {
                        getBean(beanName);
                    }
                }
            }
            // 3.2 不是FactoryBean, 利用getBean(beanName); 创建对象
            else {
                // 开始实例普通的bean
                getBean(beanName);
            }
        }
    }

    // Trigger post-initialization callback for all applicable beans...
    // 4.所有Bean都利用getBean创建完成之后，检查所有的Bean是否是SmartInitializingSingleton接口的，如果是执行afterSingletonsInstantiated()
    for (String beanName : beanNames) {
        Object singletonInstance = getSingleton(beanName);
        if (singletonInstance instanceof SmartInitializingSingleton) {
            SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
            if (System.getSecurityManager() != null) {
                AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
                    smartSingleton.afterSingletonsInstantiated();
                    return null;
                }, getAccessControlContext());
            }
            else {
                smartSingleton.afterSingletonsInstantiated();
            }
        }
    }
}

@Override
public Object getBean(String name) throws BeansException {
    return doGetBean(name, null, null, false);
}

doGetBean()

protected <T> T doGetBean(
    String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
    throws BeansException {

    // 验证bean的名字是否非法
    String beanName = transformedBeanName(name);
    Object bean;

    // Eagerly check singleton cache for manually registered singletons.
    // 1.先获取缓存中保存的单实例Bean, 如果能获取到说明这个Bean之前被创建过 
    // (所有创建过的单实例Bean都会被缓存起来)
    Object sharedInstance = getSingleton(beanName);
    if (sharedInstance != null && args == null) {
        if (logger.isTraceEnabled()) {
            if (isSingletonCurrentlyInCreation(beanName)) {
                logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +
                             "' that is not fully initialized yet - a consequence of a circular reference");
            }
            else {
                logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
            }
        }
        bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
    }
    // 2.缓存中获取不到，开始Bean的创建对象流程
    else {
        // Fail if we're already creating this bean instance:
        // We're assumably within a circular reference.
        if (isPrototypeCurrentlyInCreation(beanName)) {
            throw new BeanCurrentlyInCreationException(beanName);
        }

        // Check if bean definition exists in this factory.
        BeanFactory parentBeanFactory = getParentBeanFactory();
        if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
            // Not found -> check parent.
            String nameToLookup = originalBeanName(name);
            if (parentBeanFactory instanceof AbstractBeanFactory) {
                return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
                    nameToLookup, requiredType, args, typeCheckOnly);
            }
            else if (args != null) {
                // Delegation to parent with explicit args.
                return (T) parentBeanFactory.getBean(nameToLookup, args);
            }
            else if (requiredType != null) {
                // No args -> delegate to standard getBean method.
                return parentBeanFactory.getBean(nameToLookup, requiredType);
            }
            else {
                return (T) parentBeanFactory.getBean(nameToLookup);
            }
        }
        // 3.标记当前bean已经被创建
        if (!typeCheckOnly) {
            markBeanAsCreated(beanName);
        }

        try {
            // 4.获取Bean的定义信息
            RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
            checkMergedBeanDefinition(mbd, beanName, args);

            // Guarantee initialization of beans that the current bean depends on.
            // 5.获取当前Bean依赖的其他Bean, 若有, 则按照getBean()把依赖的Bean先创建出来
            String[] dependsOn = mbd.getDependsOn();
            if (dependsOn != null) {
                for (String dep : dependsOn) {
                    if (isDependent(beanName, dep)) {
                        throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                                                        "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
                    }
                    registerDependentBean(dep, beanName);
                    try {
                        getBean(dep);
                    }
                    catch (NoSuchBeanDefinitionException ex) {
                        throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                                                        "'" + beanName + "' depends on missing bean '" + dep + "'", ex);
                    }
                }
            }

            // Create bean instance.
            // 6.启动单实例Bean的创建流程
            if (mbd.isSingleton()) {
                sharedInstance = getSingleton(beanName, () -> {
                    try {
                        // 6.1
                        return createBean(beanName, mbd, args);
                        // 6.2 将创建的Bean添加到缓存中 SingletonObjects
                        // IOC容器就是这些Map, 很多的Map里面保存了Bean和环境信息等
                    }
                    catch (BeansException ex) {
                        // Explicitly remove instance from singleton cache: It might have been put there
                        // eagerly by the creation process, to allow for circular reference resolution.
                        // Also remove any beans that received a temporary reference to the bean.
                        destroySingleton(beanName);
                        throw ex;
                    }
                });
                bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
            }

            else if (mbd.isPrototype()) {
                // It's a prototype -> create a new instance.
                Object prototypeInstance = null;
                try {
                    beforePrototypeCreation(beanName);
                    prototypeInstance = createBean(beanName, mbd, args);
                }
                finally {
                    afterPrototypeCreation(beanName);
                }
                bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
            }

            else {
                String scopeName = mbd.getScope();
                if (!StringUtils.hasLength(scopeName)) {
                    throw new IllegalStateException("No scope name defined for bean ´" + beanName + "'");
                }
                Scope scope = this.scopes.get(scopeName);
                if (scope == null) {
                    throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
                }
                try {
                    Object scopedInstance = scope.get(beanName, () -> {
                        beforePrototypeCreation(beanName);
                        try {
                            return createBean(beanName, mbd, args);
                        }
                        finally {
                            afterPrototypeCreation(beanName);
                        }
                    });
                    bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
                }
                catch (IllegalStateException ex) {
                    throw new BeanCreationException(beanName,
                                                    "Scope '" + scopeName + "' is not active for the current thread; consider " +
                                                    "defining a scoped proxy for this bean if you intend to refer to it from a singleton",
                                                    ex);
                }
            }
        }
        catch (BeansException ex) {
            cleanupAfterBeanCreationFailure(beanName);
            throw ex;
        }
    }

    // Check if required type matches the type of the actual bean instance.
    if (requiredType != null && !requiredType.isInstance(bean)) {
        try {
            T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
            if (convertedBean == null) {
                throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
            }
            return convertedBean;
        }
        catch (TypeMismatchException ex) {
            if (logger.isTraceEnabled()) {
                logger.trace("Failed to convert bean '" + name + "' to required type '" +
                             ClassUtils.getQualifiedName(requiredType) + "'", ex);
            }
            throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
        }
    }
    return (T) bean;
}

protected Object getSingleton(String beanName, boolean allowEarlyReference) {
    Object singletonObject = this.singletonObjects.get(beanName);
    if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
        synchronized (this.singletonObjects) {
            singletonObject = this.earlySingletonObjects.get(beanName);
            if (singletonObject == null && allowEarlyReference) {
                ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
                if (singletonFactory != null) {
                    singletonObject = singletonFactory.getObject();
                    // 放到三级缓存
                    this.earlySingletonObjects.put(beanName, singletonObject);
                    // 从二级缓存清除
                    this.singletonFactories.remove(beanName);
                }
            }
        }
    }
    return singletonObject;
}

createBean()

@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
    throws BeanCreationException {

    if (logger.isTraceEnabled()) {
        logger.trace("Creating instance of bean '" + beanName + "'");
    }
    RootBeanDefinition mbdToUse = mbd;

    // Make sure bean class is actually resolved at this point, and
    // clone the bean definition in case of a dynamically resolved Class
    // which cannot be stored in the shared merged bean definition.
    Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
    if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
        mbdToUse = new RootBeanDefinition(mbd);
        mbdToUse.setBeanClass(resolvedClass);
    }

    // Prepare method overrides.
    try {
        mbdToUse.prepareMethodOverrides();
    }
    catch (BeanDefinitionValidationException ex) {
        throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
                                               beanName, "Validation of method overrides failed", ex);
    }

    // 1.解析resolveBeforeInstantiation(): 让BeanPostProcessor先拦截返回代理对象, InstantiationAwareBeanPostProcessor 提前执行, 
    // 先触发postProcessBeforeInstantiation(), 如果有返回值，则触发postProcessAfterInitialization();
    try {
        // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
        Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
        if (bean != null) {
            return bean;
        }
    }
    catch (Throwable ex) {
        throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
                                        "BeanPostProcessor before instantiation of bean failed", ex);
    }
    // 2.如果前面的InstantiationAwareBeanPostProcessor 没有返回代理对象, 则执行
    // 分析
    try {
        Object beanInstance = doCreateBean(beanName, mbdToUse, args);
        if (logger.isTraceEnabled()) {
            logger.trace("Finished creating instance of bean '" + beanName + "'");
        }
        return beanInstance;
    }
    catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
        // A previously detected exception with proper bean creation context already,
        // or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
        throw ex;
    }
    catch (Throwable ex) {
        throw new BeanCreationException(
            mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
    }
}

doCreateBean()

protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
      throws BeanCreationException {

   // Instantiate the bean.
   BeanWrapper instanceWrapper = null;
   if (mbd.isSingleton()) {
      instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
   }
   if (instanceWrapper == null) {
      // 1.实例化对象, 利用工厂方法或者对象的构造器创建出Bean实例, 里面第二次调用后置处理器
      instanceWrapper = createBeanInstance(beanName, mbd, args);
   }
   Object bean = instanceWrapper.getWrappedInstance();
   Class<?> beanType = instanceWrapper.getWrappedClass();
   if (beanType != NullBean.class) {
      mbd.resolvedTargetType = beanType;
   }

   // Allow post-processors to modify the merged bean definition.
   synchronized (mbd.postProcessingLock) {
      if (!mbd.postProcessed) {
         try {
            // 2.调用MergedBeanDefinitionPostProcessor 的postProcessMergedBeanDefinition(mbd, beanType, beanName)
            applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
         }
         catch (Throwable ex) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                  "Post-processing of merged bean definition failed", ex);
         }
         mbd.postProcessed = true;
      }
   }

   // Eagerly cache singletons to be able to resolve circular references
   // even when triggered by lifecycle interfaces like BeanFactoryAware.
   // 判断是否允许循环依赖
   boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
         isSingletonCurrentlyInCreation(beanName));
   if (earlySingletonExposure) {
      if (logger.isTraceEnabled()) {
         logger.trace("Eagerly caching bean '" + beanName +
               "' to allow for resolving potential circular references");
      }
      // 第四次调用后置处理器，判断是否需要AOP
      addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
   }

   // Initialize the bean instance.
   Object exposedObject = bean;
   try {
      // 3.Bean属性赋值(填充属性), 即常说的自动注入
      // 里面会完成第五次和第六次后置处理器的调用
      // 赋值之前: 
      // 1) 拿到InstantiationAwareBeanPostProcessor后置处理器 postProcessAfterInstantiation();
      // 2) 拿到InstantiationAwareBeanPostProcessor后置处理器 postProcessPropertyValues(); 
      // 赋值: 应用Bean属性的值, 为属性利用setter方法等进行赋值: applyPropertyValues(beanName, mbd, bw, pvs);
      populateBean(beanName, mbd, instanceWrapper);
      // 4.Bean初始化
      // 里面会进行第七次和第八次后置处理器的调用
      // 分析
      exposedObject = initializeBean(beanName, exposedObject, mbd);
   }
   catch (Throwable ex) {
      if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
         throw (BeanCreationException) ex;
      }
      else {
         throw new BeanCreationException(
               mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
      }
   }

   if (earlySingletonExposure) {
      Object earlySingletonReference = getSingleton(beanName, false);
      if (earlySingletonReference != null) {
         if (exposedObject == bean) {
            exposedObject = earlySingletonReference;
         }
         else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
            String[] dependentBeans = getDependentBeans(beanName);
            Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
            for (String dependentBean : dependentBeans) {
               if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
                  actualDependentBeans.add(dependentBean);
               }
            }
            if (!actualDependentBeans.isEmpty()) {
               throw new BeanCurrentlyInCreationException(beanName,
                     "Bean with name '" + beanName + "' has been injected into other beans [" +
                     StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
                     "] in its raw version as part of a circular reference, but has eventually been " +
                     "wrapped. This means that said other beans do not use the final version of the " +
                     "bean. This is often the result of over-eager type matching - consider using " +
                     "'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");
            }
         }
      }
   }

   // Register bean as disposable.
   // 5.注册Bean的销毁方法
   try {
      registerDisposableBeanIfNecessary(beanName, bean, mbd);
   }
   catch (BeanDefinitionValidationException ex) {
      throw new BeanCreationException(
            mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
   }

   return exposedObject;
}

initializeBean()

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
    // 1.执行Aware接口方法
    // invokeAwareMethods(beanName, bean): 执行xxxAware的方法, BeanNameAware/BeanClassLoaderAware/BeanFactoryAware
    if (System.getSecurityManager() != null) {
        AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
            invokeAwareMethods(beanName, bean);
            return null;
        }, getAccessControlContext());
    }
    else {
        invokeAwareMethods(beanName, bean);
    }

    Object wrappedBean = bean;
    if (mbd == null || !mbd.isSynthetic()) {
        // 2.执行后置处理器初始化之前
        wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
    }

    try {
        // 3.执行初始化方法
        // 3.1 是否是InitializingBean接口的实现，执行接口规定的初始化
        // 3.2 是否自定义初始化
        invokeInitMethods(beanName, wrappedBean, mbd);
    }
    catch (Throwable ex) {
        throw new BeanCreationException(
            (mbd != null ? mbd.getResourceDescription() : null),
            beanName, "Invocation of init method failed", ex);
    }
    if (mbd == null || !mbd.isSynthetic()) {
        // 4.执行后置处理器初始化之后
        wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
    }

    return wrappedBean;
}

finishRefresh()

完成BeanFactory的初始化创建工作，IOC容器就创建完成

protected void finishRefresh() {
    // Clear context-level resource caches (such as ASM metadata from scanning).
    clearResourceCaches();

    // Initialize lifecycle processor for this context.
    // 初始化和生命周期有关的后置处理器LifecycleProcessor
    // 默认从容器中找是否有LifecycleProcessor的组件，
	// 如果没有, 则new DefaultLifecycleProcessor(); 并加入到容器
    initLifecycleProcessor();

    // Propagate refresh to lifecycle processor first.
    // 拿到前面定义的生命周期处理器，回调onRefresh()
    getLifecycleProcessor().onRefresh();

    // Publish the final event.
    // 发布容器刷新完成事件
    publishEvent(new ContextRefreshedEvent(this));

    // Participate in LiveBeansView MBean, if active.
    LiveBeansView.registerApplicationContext(this);
}

总结：

1）Spring容器在启动时，会先保存所有注册进来的Bean的定义信息

• xml注册bean：bean标签
• 注解注册bean

2）Spring容器在合适的时机创建这些Bean

• 用到这个Bean的时候：利用getBean创建bean，创建好以后保存在容器中；
• 统一创建剩下所有的bean时，finishBeanFactoryInitialization()；

3）后置处理器：BeanPostProcessor

每个bean创建完成时，都会使用各种后置处理器进行处理，来增强bean的功能；

• AutowiredAnnotationBeanPostProcessor：处理自动注入；

• AnnotationAwareAspectJAutoProxyCreator：来做AOP功能；

• …

4）事件驱动模型

ApplicationListener：事件监听

ApplicationEventMulticaster：事件派发