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IOC容器启动源码6-12步分析-触发单例Bean的初始化

彭晨涛 • • 中间件/工具/框架 • 阅读 13

接着refresh()方法的第六步开始写下去：

@Override
public void refresh() throws BeansException, IllegalStateException {
    //上锁，保证只有一个线程进入
    synchronized (this.startupShutdownMonitor) {
        // 1. 准备要刷新的上下文
        prepareRefresh();

        // 2. 告诉子类去刷新内部的BeanFactory
        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

        // 3. 准备当前上下文要用的BeanFactory
        prepareBeanFactory(beanFactory);

        try {
            // 4. 在子类中允许BeanFactory的Post-processing处理
            postProcessBeanFactory(beanFactory);

            // 5. 调用所有以Bean身份注册的BeanFactoryPostProcessor
            invokeBeanFactoryPostProcessors(beanFactory);

            // 6. 注册拦截Bean创建的processors
            registerBeanPostProcessors(beanFactory);

            // 7. 初始化上下文的消息来源
            initMessageSource();

            // 8. 初始化上下文的事件多播器
            initApplicationEventMulticaster();

            // 9. 在特定的容器子类中初始化特殊的Bean
            onRefresh();

            // 10. 检查并注册监听器Bean对象
            registerListeners();

            // 11. 实例化所有的（非懒加载）单例对象
            finishBeanFactoryInitialization(beanFactory);

            // 12. 最后一步：发布对应的事件
            finishRefresh();
        }
        //捕获 BeansException 异常
        catch (BeansException ex) {
            if (logger.isWarnEnabled()) {
                logger.warn("Exception encountered during context initialization - " +
                        "cancelling refresh attempt: " + ex);
            }

            // 销毁已创建的单例对象
            destroyBeans();

            // 重置“active”标识
            cancelRefresh(ex);

            // Propagate exception to caller.
            throw ex;
        }

        finally {
            // 重置内省缓存.
            resetCommonCaches();
        }
    }
}

registerBeanPostProcessors

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
}

public static void registerBeanPostProcessors(
        ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
    // 通过BeanPostProcessor类型查找bean名称
    String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

    // 注册BeanPostProcessor之前的准备
    int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
    beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

    // 优先的PostProcessors
    List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
    // 内部的PostProcessors
    List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
    // 排序的PostProcessor的名称
    List<String> orderedPostProcessorNames = new ArrayList<>();
    // 未排序的PostProcessor的名称
    List<String> nonOrderedPostProcessorNames = new ArrayList<>();
    for (String ppName : postProcessorNames) {
        // 如果实现了PriorityOrdered接口
        if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
            // 获取BeanPostProcessor
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            // 放入priorityOrderedPostProcessors集合
            priorityOrderedPostProcessors.add(pp);
            // 如果是MergedBeanDefinitionPostProcessor，放入internalPostProcessors集合
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        // 如果实现了Ordered接口，将BeanName放入orderedPostProcessorNames集合
        else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
            orderedPostProcessorNames.add(ppName);
        }
        // 否则只将BeanName放入nonOrderedPostProcessorNames集合
        else {
            nonOrderedPostProcessorNames.add(ppName);
        }
    }

    // 按依赖顺序排序
    sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    // 首先注册实现了PriorityOrdered接口的PostProcessor
    registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

    // 然后注册实现了Ordered接口的PostProcessor
    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);

    // 注册其他PostProcessor
    List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
    for (String ppName : nonOrderedPostProcessorNames) {
        BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
        nonOrderedPostProcessors.add(pp);
        if (pp instanceof MergedBeanDefinitionPostProcessor) {
            internalPostProcessors.add(pp);
        }
    }
    registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

    // 注册所有MergedBeanDefinitionPostProcessor
    sortPostProcessors(internalPostProcessors, beanFactory);
    registerBeanPostProcessors(beanFactory, internalPostProcessors);

    beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}

可见先注册实现了PriorityOrdered接口的PostProcessor，然后是实现了Ordered接口的PostProcessor，然后是普通的PostProcessor，最后是MergedBeanDefinitionPostProcessor。

如何注册：

private static void registerBeanPostProcessors(
        ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {

    for (BeanPostProcessor postProcessor : postProcessors) {
        beanFactory.addBeanPostProcessor(postProcessor);
    }
}

public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
    Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
    // 如果原来存在，则移除
    this.beanPostProcessors.remove(beanPostProcessor);
    // 如果是InstantiationAwareBeanPostProcessor，把hasInstantiationAwareBeanPostProcessors标记为true
    if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
        this.hasInstantiationAwareBeanPostProcessors = true;
    }
    // 如果是DestructionAwareBeanPostProcessor，把hasDestructionAwareBeanPostProcessors标记为true
    if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
        this.hasDestructionAwareBeanPostProcessors = true;
    }
    //添加到beanPostProcessors集合中
    this.beanPostProcessors.add(beanPostProcessor);
}

可以看出就是添加到beanFactory的beanPostProcessors集合中，并且可以重复注册，重复注册会将其在集合中的位置移到集合末尾。

initMessageSource

MessageSource用于国际化，过完这个步骤之后IoC容器中可能会存在一个BeanName为"messageSource"，类型为MessageSource的消息源单例对象。

这里不看。

initApplicationEventMulticaster

过完这个步骤之后IoC容器中可能会存在一个BeanName为"applicationEventMulticaster"，类型为ApplicationEventMulticaster的事件广播器单例对象。

这里不看。

onRefresh

通常是Web环境

registerListeners

protected void registerListeners() {
    // 注册一些静态特定的listener
    for (ApplicationListener<?> listener : getApplicationListeners()) {
        getApplicationEventMulticaster().addApplicationListener(listener);
    }

    // 注册所有以Bean身份注册的ApplicationListener
    String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
    for (String listenerBeanName : listenerBeanNames) {
        getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
    }

    // 发布早期事件：事件广播器已建立
    Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
    this.earlyApplicationEvents = null;
    if (earlyEventsToProcess != null) {
        for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
            getApplicationEventMulticaster().multicastEvent(earlyEvent);
        }
    }
}

finishBeanFactoryInitialization

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
    // 初始化一个BeanName为"conversionService"的ConversionService对象
    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));
    }

    // 添加一个嵌入的ValueResolver
    if (!beanFactory.hasEmbeddedValueResolver()) {
        beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
    }

    // 先初始化所有实现了LoadTimeWeaverAware接口的Bean
    String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
    for (String weaverAwareName : weaverAwareNames) {
        getBean(weaverAwareName);
    }

    // 停止使用暂时的类加载器
    beanFactory.setTempClassLoader(null);

    // 冻结配置更改，允许缓存BeanDefinition元信息
    beanFactory.freezeConfiguration();

    // 初始化所有的单例对象
    beanFactory.preInstantiateSingletons();
}

冻结配置并缓存beanDefinitionNames：

@Override
public void freezeConfiguration() {
    this.configurationFrozen = true;
    this.frozenBeanDefinitionNames = StringUtils.toStringArray(this.beanDefinitionNames);
}

注意这里初始化所有的单例对象，此时就是按照单例Bean的名单一个个触发了一下getBean方法，而单独创建一个DefaultListableBeanFactory是不会启动的时候就实例化这些单例Bean的，这也是ApplicationContext和BeanFactory的区别之一：

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

    // 复制一个beanDefinitionNames的list出来
    List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

    // 触发所有非懒加载的单例对象的初始化
    for (String beanName : beanNames) {
        // 获取BeanDefinition
        RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
        // 不是抽象、是单例、不是懒加载
        if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
            // 如果是一个FactoryBean对象
            if (isFactoryBean(beanName)) {
                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<Boolean>)
                                        ((SmartFactoryBean<?>) factory)::isEagerInit,
                                getAccessControlContext());
                    }
                    else {
                        isEagerInit = (factory instanceof SmartFactoryBean &&
                                ((SmartFactoryBean<?>) factory).isEagerInit());
                    }
                    if (isEagerInit) {
                        getBean(beanName);
                    }
                }
            }
            // 如果是普通的bean对象，调用getBean获取
            else {
                getBean(beanName);
            }
        }
    }

    // 触发所有的初始化后的回调（实现了SmartInitializingSingleton接口）
    for (String beanName : beanNames) {
        Object singletonInstance = getSingleton(beanName);
        if (singletonInstance instanceof SmartInitializingSingleton) {
            final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
            if (System.getSecurityManager() != null) {
                AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
                    smartSingleton.afterSingletonsInstantiated();
                    return null;
                }, getAccessControlContext());
            }
            else {
                smartSingleton.afterSingletonsInstantiated();
            }
        }
    }
}

可以看出，就是调用getBean方法触发单例对象的初始化，而getBean方法我们已经在IOC容器启动源码第3、4、5步分析-容器加载了哪些非Bean对象？中看过了，其触发的创建Bean对象的方法createBean也在IOC容器启动源码第5步分析续-createBean到底是怎么实现的？中看过了，这里就不重复了。最终创建的单例Bean对象会放入disposableBeans集合中。

finishRefresh

初始化完所有的单例对象后，就是最后一步finishRefresh了：

protected void finishRefresh() {
    // 清除上下文级别的资源缓存
    clearResourceCaches();

    // 初始化声明周期处理器
    initLifecycleProcessor();

    // 生命周期处理器触发refresh
    getLifecycleProcessor().onRefresh();

    // 发布 ContextRefreshedEvent 事件
    publishEvent(new ContextRefreshedEvent(this));

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

第二步initLifecycleProcessor：

protected void initLifecycleProcessor() {
    ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    //如果存在名为"lifecycleProcessor"的bean对象，获取并赋值给类中的字段
    if (beanFactory.containsLocalBean(LIFECYCLE_PROCESSOR_BEAN_NAME)) {
        this.lifecycleProcessor =
                beanFactory.getBean(LIFECYCLE_PROCESSOR_BEAN_NAME, LifecycleProcessor.class);
        if (logger.isTraceEnabled()) {
            logger.trace("Using LifecycleProcessor [" + this.lifecycleProcessor + "]");
        }
    }
    // 否则进行创建
    else {
        DefaultLifecycleProcessor defaultProcessor = new DefaultLifecycleProcessor();
        defaultProcessor.setBeanFactory(beanFactory);
        this.lifecycleProcessor = defaultProcessor;
        beanFactory.registerSingleton(LIFECYCLE_PROCESSOR_BEAN_NAME, this.lifecycleProcessor);
        if (logger.isTraceEnabled()) {
            logger.trace("No '" + LIFECYCLE_PROCESSOR_BEAN_NAME + "' bean, using " +
                    "[" + this.lifecycleProcessor.getClass().getSimpleName() + "]");
        }
    }
}

LifecycleProcessor主要是负责实现了SmartLifecycle的bean的管理。其他的步骤就不看了。

原创文章，作者：彭晨涛，如若转载，请注明出处：https://www.codetool.top/article/ioc%e5%ae%b9%e5%99%a8%e5%90%af%e5%8a%a8%e6%ba%90%e7%a0%816-12%e6%ad%a5%e5%88%86%e6%9e%90-%e8%a7%a6%e5%8f%91%e5%8d%95%e4%be%8bbean%e7%9a%84%e5%88%9d%e5%a7%8b%e5%8c%96/

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