Spring IOC 源码解析四（加载非延迟单例前的操作）

引言

上一期讲述了BeanDefinitions的载入和注册，beanDefinition相当于spring对bean的数据抽象定义，这一期我们继续顺着的 refresh 方法往下讲

回到refresh方法

上一期其实主要是介绍了obtainFreshBeanFactory() 这一步，这一期我们继续接着往下看

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

        // 创建BeanFactory,并载入BeanDefinitions（重要）
        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);

            // 执行 BeanFactoryPostProcessors（实例化bean前修改bean定义信息）
            invokeBeanFactoryPostProcessors(beanFactory);

            // 注册 BeanPostProcessors（初始化bean前后执行）
            registerBeanPostProcessors(beanFactory);

            // Initialize message source for this context.
            // 国际化相关
            initMessageSource();

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

            // Initialize other special beans in specific context subclasses.
            // 初始化主题信息
            onRefresh();

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

            // 提前实例化化全部非延迟加载的单例类型
            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();
        }
    }
}

prepareBeanFactory(beanFactory)

先看一下prepareBeanFactory的方法实现

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
    // 配置容器的 classLoader
    beanFactory.setBeanClassLoader(getClassLoader());
    // 这是一个表达是语言处理器
    beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
    // 属性编辑器
    beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

    // 配置了BeanPostProcessor的一个实现类
    beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
    // 配置被忽略的依赖项（各种 Aware 实现类）
    beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
    beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
    beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
    beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
    beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
    beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

    // 修正依赖
    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.
    // 注册AOP相关的
    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()));
    }

    // 配置Spring 默认环境变量bean
    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());
    }
}

这个方法做了什么事情呢，我们简单的来看一下

• 首先是配置了容器的默认 classLoader
• 配置了一个语言器和一个属性编辑器
• 注册了一个BeanPostProcessor接口的一个实现类，这个接口的具体用处下面马上会讲到
• 配置要自动注入时要被忽略的bean类型，可以看到这里配置的都是一些Aware实现类，这些依赖项spring容器会统一设置
• 注册aop相关的
• 配置Spring默认环境变量bean(systemProperties, systemEnvironment, environment)

postProcessBeanFactory(beanFactory)

方法比较简短，通过查看代码，可知也是对beanFactory做一些配置的工作

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);
}

invokeBeanFactoryPostProcessors(beanFactory)

可以看到主要逻辑在，PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors中，这里其实是spring留的一个扩展点，我们可以通过实现BeanFactoryPostProcessor来实现在 getBean之前的自定义扩展。现在我们就来看看它是在什么时候执行的

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    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()));
    }
}

继续查看PostProcessorRegistrationDelegate.class

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

    // 存放已经执行的 BeanFactoryPostProcessor bean名字
    Set<String> processedBeans = new HashSet<String>();

    // 判断beanFactory类型是否为BeanDefinitionRegistry，只有BeanDefinitionRegistry类型的才支持BeanDefinitionRegistryPostProcessor的注册
    if (beanFactory instanceof BeanDefinitionRegistry) {
        BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
        // 存放手动加入的 BeanFactoryPostProcessor
        List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
        // 存放手动加入的 BeanDefinitionRegistryPostProcessor
        List<BeanDefinitionRegistryPostProcessor> registryProcessors = new LinkedList<BeanDefinitionRegistryPostProcessor>();

        for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
        // 如果是BeanDefinitionRegistryPostProcessor类型
            if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                BeanDefinitionRegistryPostProcessor registryProcessor =
                        (BeanDefinitionRegistryPostProcessor) postProcessor;
                // 执行 postProcessBeanDefinitionRegistry 方法
                registryProcessor.postProcessBeanDefinitionRegistry(registry);
                // 放入待执行容器中，之后会执行BeanFactoryPostProcessor接口的postProcessBeanFactory方法
                registryProcessors.add(registryProcessor);
            }
            else {
                // 放入待执行容器中，之后统一执行 
                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.
        // 用于存放当前需要执行的 BeanDefinitionRegistryPostProcessor list
        List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();

        // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
        // 一 先执行类型为 PriorityOrdered 的BeanDefinitionRegistryPostProcessors
        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);
            }
        }
        // 排序
        sortPostProcessors(currentRegistryProcessors, beanFactory);
        // 将当前需要执行全部放入 待执行容器
        registryProcessors.addAll(currentRegistryProcessors);
        // 执行
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        // 清空已经执行过的
        currentRegistryProcessors.clear();

        // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
        // 二 在执行类型为Ordered的BeanDefinitionRegistryPostProcessor
        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.
        // 最后执行普通的 BeanDefinitionRegistryPostProcessors
        boolean reiterate = true;
        // 循环的目的是未了防止执行过程中有新的 postProcessorNames 加入
        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.
        // 执行待执行容器的中的 BeanFactoryPostProcessor 
        invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
        invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
    }

    else {
        // Invoke factory processors registered with the context instance.
        // 直接执行手动加入的 BeanFactoryPostProcessor
        invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
    }


    // 以上执行完BeanDefinitionRegistryPostProcessor，现在开始执行BeanFactoryPostProcessor
    String[] postProcessorNames =
            beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

    // 执行顺序和BeanDefinitionRegistryPostProcessor基本一致，先PriorityOrdered，再Ordered，最后普通的
    List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
    // 存放 PriorityOrdered类型的BeanFactoryPostProcessor
    List<String> orderedPostProcessorNames = new ArrayList<String>();
    // 存放 Ordered类型的BeanFactoryPostProcessor
    List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
    for (String ppName : postProcessorNames) {
        if (processedBeans.contains(ppName)) {
            // 这里跳过的是已经执行过的 BeanDefinitionRegistryPostProcessor
            // 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.
    // 先执行 PriorityOrdered
    sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

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

    // Finally, invoke all other BeanFactoryPostProcessors.
    // 最后执行普通的
    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();
}

这个方法代码非常的多，夹杂着各种判断，看的眼花缭乱。我们简单理一下逻辑

1. BeanFactoryPostProcessor有一个子接口叫做BeanDefinitionRegistryPostProcessor，它的优先级是比BeanFactoryPostProcessor高的
2. 方法的入参里有一个List<BeanFactoryPostProcessor> beanFactoryPostProcessors，这个是容器通过addBeanFactoryPostProcessor方法手动加入的。这里的BeanDefinitionRegistryPostProcessor类型是优先级最高的
3. 同时BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor可以都实现两个接口(PriorityOrdered,Ordered)用来定义执行的顺序，其中PriorityOrdered优先级最高，其次Ordered，最后是没有实现任何Order接口的

综上三点，我们是可以得出上面一大坨代码的执行顺序了

• 首先是拿到手动加入的BeanFactoryPostProcessor，挑出里面的BeanDefinitionRegistryPostProcessor类型，优先执行。
• 再拿到容器中的全部BeanDefinitionRegistryPostProcessors，按照实现的排序接口顺序执行
• 执行BeanDefinitionRegistryPostProcessors父类型BeanFactoryPostProcessor的方法
• 最后再拿到容器中全部BeanFactoryPostProcessors并过滤到已经执行过的BeanDefinitionRegistryPostProcessors，按照顺序依次执行

registerBeanPostProcessors(beanFactory)

这里也是spring的一个扩展点，通过实现BeanPostProcessor接口来实现自定义逻辑，具体的执行时机，会在分析getBaan时讲到，这里的逻辑仅仅是将BeanPostProcessor用户自定义的BeanPostProcessor注册到容器

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.
    sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

    // Next, register the BeanPostProcessors that implement Ordered.
    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(orderedPostProcessors, beanFactory);
    registerBeanPostProcessors(beanFactory, orderedPostProcessors);

    // Now, register all regular BeanPostProcessors.
    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.
    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).
    beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}

这里的逻辑其实跟上面的逻辑非常的相似，其实也都在一个class中，唯一的区别是这里并没有执行，仅仅只是做了下排序后就注册进了容器中，留到后面的步骤中在执行。这里也简单的列一下这里的要点

1. BeanPostProcessor有一个子接口MergedBeanDefinitionPostProcessor,这个是最晚被注册进容器的
2. 同样可以实现(PriorityOrdered,Ordered)接口用来定义执行的顺序

initMessageSource()

国际化相关，这里就不做仔细分析了

initApplicationEventMulticaster()

顾名思义。就是spring用来初始化事情广播器的

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.isDebugEnabled()) {
            logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
        }
    }
    else {
        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 + "]");
        }
    }
}

看一下这里的代码比较的简单，就是一个 if else，先尝试获取名字为APPLICATION_EVENT_MULTICASTER_BEAN_NAME类型为ApplicationEventMulticaster的 bean，如果没有获取到，则配置一个默认的bean (SimpleApplicationEventMulticaster)

onRefresh()

这里是留给子类实现的，没有什么逻辑

registerListeners()

注册一些监听器

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...
    Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
    this.earlyApplicationEvents = null;
    if (earlyEventsToProcess != null) {
        for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
            getApplicationEventMulticaster().multicastEvent(earlyEvent);
        }
    }
}

尾言

下篇会解析finishBeanFactoryInitialization方法，并且会着重讲解初始化bean的整个生命周期
博客原文地址戳这里