Spring5源码解析8-refresh方法总结

废话不多说，直接上源码注释：

//AbstractApplicationContext#refresh源码
public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
        // Prepare this context for refreshing.
        //准备上下文,设置其启动日期和活动标志,执行属性源的初始化
        prepareRefresh();

        // Tell the subclass to refresh the internal bean factory.
        //调用子类 refreshBeanFactory()方法
        //获取 BeanFactory 实例 DefaultListableBeanFactory , DefaultListableBeanFactory 实现了 ConfigurableListableBeanFactory 接口
        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

        // Prepare the bean factory for use in this context.
        //配置 beanFactory 上下文
        //1.添加 ApplicationContextAwareProcessor 和 ApplicationListenerDetector
        //2.忽略部分类型的自动装配
        //3.注册特殊的依赖类型，并使用相应的autowired值
        //4.注册默认的environment beans
        //5.设置environment beans
        prepareBeanFactory(beanFactory);

        try {
            // Allows post-processing of the bean factory in context subclasses.
            //留给子类去扩展的一个方法
            postProcessBeanFactory(beanFactory);

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

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

            // Initialize message source for this context.
            // 初始化信息源,作国际化相关
            initMessageSource();

            // Initialize event multicaster for this context.
            // 初始化容器实现传播器,也就是往容器中添加了一个Bean
            initApplicationEventMulticaster();

            // Initialize other special beans in specific context subclasses.
            // 在特定 ApplicationContext 的子类中触发某些特殊的Bean初始化
            // 在此处AbstractApplicationContext.onRefresh 是一个空方法
            onRefresh();

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

            // Instantiate all remaining (non-lazy-init) singletons.
            // 初始化所有还未被初始化的单例bean
            finishBeanFactoryInitialization(beanFactory);

            // Last step: publish corresponding event.
            // 容器启动完成,清理缓存, 发布 ContextRefreshedEvent 事件
            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.
            // 销毁已创建的单例bean
            destroyBeans();

            // Reset 'active' flag.
            // 取消Refresh,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...
            // 清理缓存信息
            resetCommonCaches();
        }
    }
}

之前已经分析到了invokeBeanFactoryPostProcessors方法，现在来看一下
registerBeanPostProcessors。

registerBeanPostProcessors

registerBeanPostProcessors，顾名思义主要在注册BeanPostProcessor，改方法的具体逻辑委托给了PostProcessorRegistrationDelegate#registerBeanPostProcessors方法，我们直接来看该方法源码：

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

    //从 beanDefinitionNames 中获取类型为 BeanPostProcessor 的 beanName
    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.
    // BeanPostProcessorChecker 实现了 BeanPostProcessor接口
    // 用来判断当前 bean 是否已经执行了所有的 BeanPostProcessor
    int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
    beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

    // Separate between BeanPostProcessors that implement PriorityOrdered,
    // Ordered, and the rest.
    // 对 BeanPostProcessor 进行分类排序
    // 实现 PriorityOrdered 接口的 BeanPostProcessor
    List priorityOrderedPostProcessors = new ArrayList<>();
    // 实现 MergedBeanDefinitionPostProcessor 接口的 BeanPostProcessor
    List internalPostProcessors = new ArrayList<>();
    // 实现 Ordered 接口的 BeanPostProcessor 的 BeanName
    List orderedPostProcessorNames = new ArrayList<>();
    // 普通的 BeanPostProcessor 的 BeanName
    List nonOrderedPostProcessorNames = new ArrayList<>();
    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.
    sortPostProcessors(priorityOrderedPostProcessors, beanFactory);

    // 注册实现 PriorityOrdered 接口的 BeanPostProcessor
    // 底层循环List调用 beanFactory.addBeanPostProcessor(postProcessor); 方法
    registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

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

    // 注册实现 Ordered 接口的 BeanPostProcessor
    registerBeanPostProcessors(beanFactory, orderedPostProcessors);

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

    //注册普通的 BeanPostProcessor
    registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

    // Finally, re-register all internal BeanPostProcessors.
    sortPostProcessors(internalPostProcessors, beanFactory);
    //注册实现 MergedBeanDefinitionPostProcessor 接口的 BeanPostProcessor
    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).
    beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}

是不是有种似曾相识的感受，嗯...这个源码的内部套路和invokeBeanFactoryPostProcessors方法差不多。

1. 从beanDefinitionNames中获取类型为BeanPostProcessor的所有beanName

2. 遍历所有的postProcessorNames，将其分类：

   • 实现PriorityOrdered接口的
   • 实现MergedBeanDefinitionPostProcessor接口的
   • 实现Ordered接的
   • 普通的BeanPostProcessor
3. 按一定是先后顺序依次执行所有的为BeanPostProcessor，具体可查看上述源码。

initMessageSource

initMessageSource方法负责，初始化信息源,是一些国际化相关功能，我们忽略。

initApplicationEventMulticaster

初始化容器实现传播器,也就是往容器中添加了一个Bean，具体代码如下：

protected void initApplicationEventMulticaster() {
    ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    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 + "]");
        }
    } else {
        this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
        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

onRefresh方法在此处AbstractApplicationContext.onRefresh是一个空方法，其作用是在特定ApplicationContext的子类中触发某些特殊的Bean初始化。

registerListeners

注册ApplicationListener，源码如下：

protected void registerListeners() {
    // Register statically specified listeners first.
    // 这里的 applicationListeners 是需要我们手动调用 AbstractApplicationContext.addApplicationListener 方法才会有内容
    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!
    // 默认情况下,这里也是空
    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...
    // 默认情况下,这里还是空
    Set earlyEventsToProcess = this.earlyApplicationEvents;
    this.earlyApplicationEvents = null;
    if (earlyEventsToProcess != null) {
        for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
            getApplicationEventMulticaster().multicastEvent(earlyEvent);
        }
    }
}

finishBeanFactoryInitialization(beanFactory);

初始化所有还未被初始化的单例bean。
AbstractApplicationContext#finishBeanFactoryInitialization
调用DefaultListableBeanFactory#preInstantiateSingletons：

//DefaultListableBeanFactory#preInstantiateSingletons源码：
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.
    // 获取所有的beanDefinitionNames
    List beanNames = new ArrayList<>(this.beanDefinitionNames);

    // Trigger initialization of all non-lazy singleton beans...
    // 遍历所有的beanDefinitionNames
    for (String beanName : beanNames) {
        // 根据指定的beanName获取其父类的相关公共属性,返回合并的RootBeanDefinition
        RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
        // 如果不是抽象类,而且是单例,又不是懒加载
        if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
            // 判断是不是FactoryBean
            if (isFactoryBean(beanName)) {
                // 如果是FactoryBean,使用 &+beanName ,去获取 FactoryBean
                // 为什么要这样做,因为beanName获取的是FactoryBean生产的Bean,要获取FactoryBean本身,需要通过&+beanName
                // 其实,实例化所有的非懒加载单例Bean的时候,如果是FactoryBean,这里只是创建了FactoryBean
                // 什么时候去创建由FactoryBean产生的Bean呢? 好像也是懒加载的,在使用到这个Bean的时候,才通过FactoryBean去创建Bean
                Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
                if (bean instanceof FactoryBean) {
                    final FactoryBean factory = (FactoryBean) bean;
                    boolean isEagerInit;
                    if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                        isEagerInit = AccessController.doPrivileged((PrivilegedAction)
                                        ((SmartFactoryBean) factory)::isEagerInit,
                                getAccessControlContext());
                    } else {
                        isEagerInit = (factory instanceof SmartFactoryBean &&
                                ((SmartFactoryBean) factory).isEagerInit());
                    }
                    if (isEagerInit) {
                        getBean(beanName);
                    }
                }
            } else {
                // 不是FactoryBean
                getBean(beanName);
            }
        }
    }

    // Trigger post-initialization callback for all applicable beans...
    for (String beanName : beanNames) {
        Object singletonInstance = getSingleton(beanName);
        // Spring容器的一个拓展点SmartInitializingSingleton
        // 在所有非懒加载单例Bean创建完成之后调用该接口 @since 4.1
        if (singletonInstance instanceof SmartInitializingSingleton) {
            final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
            if (System.getSecurityManager() != null) {
                AccessController.doPrivileged((PrivilegedAction