Spring IoC 容器的擴展

前言

本系列所有基於 Spring 5.2.2.BUILD-SNAPSHOT 版本。由於 Spring 整個體系太過於龐大,因此只會進行關鍵部分的源碼解析。html

本篇文章主要介紹 Spring IoC 容器的功能擴展。java

正文

咱們平時在使用 Spring 時,大多不會直接使用 BeanFactory,使用比較多的是 ApplicationContext;那麼在 Spring 中 BeanFactoryApplicationContext 有什麼區別呢?git

  • BeanFactory 這個接口提供了高級配置的機制的管理對象,是一個基本的 IoC 的容器。
  • ApplicationContextBeanFactory 的一個子接口,提供了 BeanFactory 的所有功能,而且在此基礎上還提供了:
    • 面向切面 (AOP)
    • 配置元信息 (Configuration Metadata)
    • 資源管理 (Resources)
    • 事件 (Events)
    • 國際化 (i18n)
    • 註解 (Annotations)
    • Environment 抽象 (Environment Abstraction)

真正的底層 IoC 容器是 BeanFactory 的實現類,ApplicationContext 中的 getBean() 其實都是委託給 DefaultListableBeanFactory 來實現。github

其中核心流程都在 AbstractApplicationContext#refresh() 方法中,咱們直接從這個方法開始。spring

容器刷新

AbstractApplicationContext#refresh

public void refresh() throws BeansException, IllegalStateException {
    // 加鎖
    synchronized (this.startupShutdownMonitor) {
        // 準備刷新的上下文環境,見下文詳解
        prepareRefresh();

        // 獲取刷新後的beanFactory,通常都是建立一個DefaultListableBeanFactory,見下文詳解
        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

        // 使用當前上下文環境準備beanFactory,見下文詳解
        prepareBeanFactory(beanFactory);

        try {
            // beanFactory的後置處理,子類實現,這也算是beanFactory的擴展點
            // AbstractRefreshableWebApplicationContext在這個方法內加入了request和session的做用域
            postProcessBeanFactory(beanFactory);

            // 調用全部BeanFactoryPostProcessors的實現類,見下文詳解
            invokeBeanFactoryPostProcessors(beanFactory);

            // 註冊BeanPostProcessors,見下文詳解
            registerBeanPostProcessors(beanFactory);

            // 初始化消息資源,這裏不作過多分析
            initMessageSource();

            // 初始化事件傳播器,這裏不作過多分析
            initApplicationEventMulticaster();

            // 在特殊的上下文環境中初始化指定的bean,模板方法留給子類實現
            onRefresh();

            // 註冊監聽器,這裏不作過多分析
            registerListeners();

            // 實例化全部非延遲加載的單例bean,見下文詳解
            finishBeanFactoryInitialization(beanFactory);

            // 完成上下文的刷新,調用生命週期處理器的onRefresh()而且發佈上下文刷新完成事件,這裏不作過多分析
            finishRefresh();
        }
        // 省略異常處理
        finally {
            // 重置緩存,例如方法、字段等
            resetCommonCaches();
        }
    }
}

上面方法就是上下文刷新的流程, 其中關於消息資源和事件的處理這裏就不分析了,後續可能會單獨分析一下 Spring 中的事件。緩存

上下文刷新前的環境準備

AbstractApplicationContext#prepareRefresh

protected void prepareRefresh() {
    // 記錄開始時間
    this.startupDate = System.currentTimeMillis();
    // 上下文關閉標識設置爲 false
    this.closed.set(false);
    // 上下文激活標識設置爲 true
    this.active.set(true);

    // 初始化佔位符屬性資源,該方法是留給子類實現的,默認什麼也不作
    initPropertySources();

    // 驗證須要的屬性文件是否都已經放入環境中
    getEnvironment().validateRequiredProperties();

    if (this.earlyApplicationListeners == null) {
        this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
    } else {
        // 在上下文刷新前重置監聽器
        this.applicationListeners.clear();
        this.applicationListeners.addAll(this.earlyApplicationListeners);
    }

    this.earlyApplicationEvents = new LinkedHashSet<>();
}

得到新的 BeanFactory

AbstractApplicationContext#obtainFreshBeanFactory

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
    // 刷新 bean 工廠,見下文詳解
    refreshBeanFactory(); 
    // 返回 bean 工廠,見下文詳解
    return getBeanFactory(); 
}

AbstractRefreshableApplicationContext#refreshBeanFactory

protected final void refreshBeanFactory() throws BeansException {
    // 若是有beanFactory
    if (hasBeanFactory()) {
        // 銷燬全部的單例bean
        destroyBeans();
        // 關閉beanFactory,也就是將beanFactory設置爲null
        closeBeanFactory();
    }
    try {
        // 建立 DefaultListableBeanFactory
        DefaultListableBeanFactory beanFactory = createBeanFactory();
        // 指定序列化id
        beanFactory.setSerializationId(getId());
        // 定製beanFactory,設置相關屬性
        customizeBeanFactory(beanFactory);
        // 加載beanDefinition
        loadBeanDefinitions(beanFactory);
        synchronized (this.beanFactoryMonitor) {
            // 加鎖,將beanFactory賦值給全局變量
            this.beanFactory = beanFactory;
        }
    }
    // 省略異常處理...
}

AbstractRefreshableApplicationContext#getBeanFactory

public final ConfigurableListableBeanFactory getBeanFactory() {
    // 加鎖
    synchronized (this.beanFactoryMonitor) {
        // 若是beanFactory爲空拋出異常
        if (this.beanFactory == null) {
            throw new IllegalStateException("BeanFactory not initialized or already closed - call 'refresh' before accessing beans via the ApplicationContext");
        }
        // 返回beanFactory
        return this.beanFactory;
    }
}

對 BeanFactory 進行功能填充

AbstractApplicationContext#prepareBeanFactory

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
    // 設置beanFactory的classLoader爲當前context的classLoader
    beanFactory.setBeanClassLoader(getClassLoader());
    // 設置beanFactory的表達式語言處理器
    beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
    // 爲beanFactory增長了一個的propertyEditor,這個主要是對bean的屬性等設置管理的一個工具
    beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

    // 添加bean擴展,主要是對ApplicationContext新增長的Aware接口進行調用
    beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

    // 設置幾個忽略自動裝配的接口
    beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
    beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
    beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
    beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
    beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
    beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

    // 註冊解決依賴,也就是說咱們能夠經過依賴注入來注入如下四種類型的bean
    beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
    beanFactory.registerResolvableDependency(ResourceLoader.class, this);
    beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
    beanFactory.registerResolvableDependency(ApplicationContext.class, this);

    // 將是ApplicationListener類型的bean在BeanPostProcessor的初始化後回調方法中加入到context的監聽器列表中
    beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

    // 增長對AspectJ支持
    if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
        beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
        beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
    }

    // 若是beanFactory不存在名爲environment的bean,添加默認的,該bean就和咱們正常聲明的單例bean同樣
    if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
        beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
    }
    // 若是beanFactory不存在名爲systemProperties的bean,添加默認的,該bean就和咱們正常聲明的單例bean同樣
    if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
        beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
    }
    // 若是systemEnvironment不存在名爲systemEnvironment的bean,添加默認的,該bean就和咱們正常聲明的單例bean同樣
    if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
        beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
    }
}

調用 BeanFactory 的處理器

AbstractApplicationContext#invokeBeanFactoryPostProcessors

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    // 實例化並調用全部已註冊的BeanFactoryPostProcessor
    PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

    if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
        beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
        beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
    }
}

PostProcessorRegistryDelegate#invokeBeanFactoryPostProcessors

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

    Set<String> processedBeans = new HashSet<>();
    // 判斷beanFactory是不是BeanDefinitionRegistry類型
    // 一般狀況下這裏的beanFactory是DefaultListableBeanFactory因此這裏判斷爲true
    if (beanFactory instanceof BeanDefinitionRegistry) {
        BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
        // 保存實現了BeanFactoryPostProcessor bean的集合
        List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
        // 保存實現了BeanDefinitionRegistryPostProcessor bean的集合
        List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
        // 遍歷beanFactoryPostProcessors
        for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
            // 找出是BeanDefinitionRegistryPostProcessor類型的並調用其postProcessBeanDefinitionRegistry()
            if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                BeanDefinitionRegistryPostProcessor registryProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor;
                registryProcessor.postProcessBeanDefinitionRegistry(registry);
                // 將BeanDefinitionRegistryPostProcessor類型的添加進registryProcessors
                registryProcessors.add(registryProcessor);
            }
            else {
                // 將BeanFactoryPostProcessor類型的添加進regularPostProcessors
                regularPostProcessors.add(postProcessor);
            }
        }

        List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

        // 獲取全部BeanDefinitionRegistryPostProcessor類型的beanName
        String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
        // 遍歷postProcessorNames
        for (String ppName : postProcessorNames) {
            // 若是實現了PriorityOrdered接口,
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                // 初始化此bean並添加進currentRegistryProcessors
                currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                // 將此beanName添加到已處理的記錄中
					processedBeans.add(ppName);
            }
        }
        // 排序
        sortPostProcessors(currentRegistryProcessors, beanFactory);
        // 將全部BeanDefinitionRegistryPostProcessor類型而且實現了PriorityOrdered接口的bean添加進registryProcessors
        registryProcessors.addAll(currentRegistryProcessors);
        // 遍歷調用currentRegistryProcessors中的全部BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry()
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        // 清空currentRegistryProcessors
        currentRegistryProcessors.clear();

        // 和上面的差很少只是此次是實現了Ordered接口的,而且沒有處理過的
        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();

        // 和上面的差很少只是此次是全部的實現了BeanDefinitionRegistryPostProcessors的bean,而且沒有處理過的
        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();
        }

        // 調用BeanFactoryPostProcessor的postProcessBeanFactory()
        invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
        invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
    }
    else {
        invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
    }

    // 獲取全部BeanFactoryPostProcessor類型的beanName
    String[] postProcessorNames =
        beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

    List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
    List<String> orderedPostProcessorNames = new ArrayList<>();
    List<String> nonOrderedPostProcessorNames = new ArrayList<>();
    // 遍歷postProcessorNames
    for (String ppName : postProcessorNames) {
        // 若是已經處理過,直接跳過;由於BeanDefinitionRegistryPostProcessor繼承於BeanFactoryPostProcessor
        // 因此postProcessorNames也包含BeanDefinitionRegistryPostProcessor類型的bean,這裏會對BeanDefinitionRegistryPostProcessor類型的bean直接跳過
        if (processedBeans.contains(ppName)) {
        }
        // 若是實現了PriorityOrdered接口,初始化該bean並添加進priorityOrderedPostProcessors
        else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
            priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
        }
        // 若是實現了Ordered接口,將beanName添加進orderedPostProcessorNames
        else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
            orderedPostProcessorNames.add(ppName);
        }
        // 正常的將beanName添加進nonOrderedPostProcessorNames
        else {
            nonOrderedPostProcessorNames.add(ppName);
        }
    }

    // 排序,而後調用BeanFactoryPostProcessors的postProcessBeanFactory()
    sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

    // 和上面的同樣這裏是實現了Ordered接口的
    List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
    for (String postProcessorName : orderedPostProcessorNames) {
        orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    sortPostProcessors(orderedPostProcessors, beanFactory);
    invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

    // 和上面的同樣這裏是正常的BeanFactoryPostProcessors
    List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
    for (String postProcessorName : nonOrderedPostProcessorNames) {
        nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

    beanFactory.clearMetadataCache();
}

上面代碼首先找出 BeanDefinitionRegistryPostProcessorBeanFactoryPostProcessor 類型的 bean,而後根據其實現的排序接口,來分別進行初始化以及調用其回調方法。能夠把 PriorityOrdered 理解爲 超級會員Ordered普通會員,都未實現的理解爲 普通用戶,優先級一個比一個高。session

咱們首先看一下 BeanFactoryPostProcessor 接口的定義:app

@FunctionalInterface
public interface BeanFactoryPostProcessor {

    /**
     * 容器初始化後,bean實例化以前調用,能夠在此修改BeanDefinition
     */
    void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;

}

能夠看出 BeanFactoryPostProcessor 接口是 Spring 初始化 BeanFactory 時對外暴露的擴展點,Spring IoC 容器容許 BeanFactoryPostProcessor 在容器實例化任何 bean 以前讀取 bean 的定義,並能夠修改它。工具

接下里咱們看一下 BeanDefinitionRegistryPostProcessor 接口的定義:post

public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {

    void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;

}

BeanDefinitionRegistryPostProcessorBeanFactoryPostProcessor 具備更高的優先級,從上面解析的代碼中就能夠看出,主要用來在 BeanFactoryPostProcessor 以前註冊其它 bean 的定義。

註冊 Bean 的處理器

AbstractApplicationContext#registerBeanPostProcessors

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

//PostProcessorRegistrationDelegate.java
public static void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
   // 獲取全部實現了BeanPostProcessor的beanName
   // 這裏會獲取到AutowiredAnnotationProcessor和CommonAnnotationProcessor後置處理器的beanName
   String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

   // 已經註冊進beanFactory的數量 + 手動註冊的BeanPostProcessorChecker + 實現了BeanPostProcessor還未註冊的bean的數量
   int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
   beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

   // 存儲實現了PriorityOrdered接口的BeanPostProcessors
   List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
   // 存儲實現了MergedBeanDefinitionPostProcessor接口的BeanPostProcessors
   List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
   // 存儲實現了Ordered接口的BeanPostProcessors
   List<String> orderedPostProcessorNames = new ArrayList<>();
   // 存儲正常的BeanPostProcessors
   List<String> nonOrderedPostProcessorNames = new ArrayList<>();

   for (String ppName : postProcessorNames) {
       // 若是實現了BeanPostProcessor的bean實現了PriorityOrdered接口
       if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
           // 獲取bean實例
           BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
           // 添加進priorityOrderedPostProcessors
           priorityOrderedPostProcessors.add(pp);
           // 若是bean也實現了MergedBeanDefinitionPostProcessor,則添加進internalPostProcessors
           if (pp instanceof MergedBeanDefinitionPostProcessor) {
               internalPostProcessors.add(pp);
           }
       }
       // 若是實現了Ordered接口,添加進orderedPostProcessorNames
       else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
           orderedPostProcessorNames.add(ppName);
       }
       // 不然添加進nonOrderedPostProcessorNames
       else {
           nonOrderedPostProcessorNames.add(ppName);
       }
   }

   // 將實現了PriorityOrdered的BeanPostProcessors先排序再註冊進beanFactory
   sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
   registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

   // 將實現了Order的BeanPostProcessors先排序再註冊進beanFactory
   List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
   for (String ppName : orderedPostProcessorNames) {
       BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
       orderedPostProcessors.add(pp);
       // 若是實現了MergedBeanDefinitionPostProcessor
       if (pp instanceof MergedBeanDefinitionPostProcessor) {
           // 添加進internalPostProcessors
           internalPostProcessors.add(pp);
       }
   }
   sortPostProcessors(orderedPostProcessors, beanFactory);
   registerBeanPostProcessors(beanFactory, orderedPostProcessors);

   // 將正常的BeanPostProcessors註冊進beanFactory
   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);

   // 最後將實現MergedBeanDefinitionPostProcessor的BeanPostProcessors先排序再註冊進beanFactory
   sortPostProcessors(internalPostProcessors, beanFactory);
   registerBeanPostProcessors(beanFactory, internalPostProcessors);

   // 這裏再次添加了ApplicationListenerDetector(以前在prepareBeanFactory()已經添加過)是爲了獲取代理
   beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}

上面代碼最後的部分會把實現了 MergedBeanDefinitionPostProcessor 會在最後從新註冊一遍,你們可能會認爲這不就重複註冊了嗎,其實否則,beanFactory#addBeanPostProcessor() 會首先刪除老的,再從新添加新的。

根據上面代碼你們也會發現,ApplicationContext 會幫咱們自動註冊實現了 BeanPostProcessorsbean,而使用 BeanFactory 就須要本身手動註冊了。

注意:上面只是註冊,真正調用是在 getBean() 的時候。

初始化非懶加載的單例 bean

AbstractApplicationContext#finishBeanFactoryInitialization

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

    if (!beanFactory.hasEmbeddedValueResolver()) {
        beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
    }

    String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
    for (String weaverAwareName : weaverAwareNames) {
        getBean(weaverAwareName);
    }

    beanFactory.setTempClassLoader(null);

    // 凍結全部的bean定義,也就是bean定義將不被修改或任何進一步的處理
    beanFactory.freezeConfiguration();

    // 初始化非延遲的單例bean,見下文詳解
    beanFactory.preInstantiateSingletons();
}

DefaultListableBeanFactory#preInstantiateSingletons

public void preInstantiateSingletons() throws BeansException {
    List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

    for (String beanName : beanNames) {
        // 獲取合併的BeanDefinition
        RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
        // bean不是抽象類 && bean是單例做用域 && bean不是延遲加載
        if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
            // 若是bean的FactoryBean
            if (isFactoryBean(beanName)) {
                // 獲取FactoryBean的實例,前面加了&符號
                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 {
                        // FactoryBean是否提早初始化
                        isEagerInit = (factory instanceof SmartFactoryBean &&
                                       ((SmartFactoryBean<?>) factory).isEagerInit());
                    }
                    // 若是是提早初始化直接調用getBean()去初始化bean
                    if (isEagerInit) {
                        getBean(beanName);
                    }
                }
            }
            // 直接調用getBean()去初始化bean
            else {
                getBean(beanName);
            }
        }
    }

    for (String beanName : beanNames) {
        // 獲取上面初始化後的單例bean
        Object singletonInstance = getSingleton(beanName);
        // 若是bean實現了SmartInitializingSingleton接口,調用afterSingletonsInstantiated()
        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();
            }
        }
    }
}

上面代碼中的 getMergedLocalBeanDefinition()Spring IoC bean 的建立有解析過,這裏再也不贅述。這裏介紹一下 SmartInitializingSingleton 接口,先看下該接口的定義:

public interface SmartInitializingSingleton {

	/**
	 * 單例bean初始化完成以後調用
	 */
	void afterSingletonsInstantiated();

}

這個接口比較簡單,就一個方法,而且只在 preInstantiateSingletons() 中調用了,也就是說你直接使用 BeanFactory 是不會調用該回調方法的。該接口回調方法在單例 bean 初始化完成以後調用後執行,屬於 Spring Bean 生命週期的加強。

完成刷新

AbstractApplicationContext#finishRefresh

protected void finishRefresh() {
    // 清除資源緩存
    clearResourceCaches();
		
    // 爲此上下文初始化生命週期處理器,見下文詳解
    initLifecycleProcessor();
		
    // 首先將刷新完畢事件傳播到生命週期處理器,見下詳解
    getLifecycleProcessor().onRefresh();

    // 發佈上下文刷新完成的事件
    publishEvent(new ContextRefreshedEvent(this));

    LiveBeansView.registerApplicationContext(this);
}

AbstractApplicationContext#initLifecycleProcessor

protected void initLifecycleProcessor() {
    // 若是當前beanFactory中含有名稱爲lifecycleProcessor的bean定義,初始化該bean並賦值給全局變量lifecycleProcessor
    ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    if (beanFactory.containsLocalBean(LIFECYCLE_PROCESSOR_BEAN_NAME)) {
        this.lifecycleProcessor = beanFactory.getBean(LIFECYCLE_PROCESSOR_BEAN_NAME, LifecycleProcessor.class);
    } else {
        // beanFactory中沒有名稱爲lifecycleProcessor的bean定義,建立一個DefaultLifecycleProcessor並當作單例bean註冊進beanFactory
        DefaultLifecycleProcessor defaultProcessor = new DefaultLifecycleProcessor();
        defaultProcessor.setBeanFactory(beanFactory);
        this.lifecycleProcessor = defaultProcessor;
        beanFactory.registerSingleton(LIFECYCLE_PROCESSOR_BEAN_NAME, this.lifecycleProcessor);
    }
}

DefaultLifecycleProcessor#onRefresh

public void onRefresh() {
    startBeans(true);
    this.running = true;
}

private void startBeans(boolean autoStartupOnly) {
    // 獲取全部實現了Lifecycle或者SmartLifecycle的單例bean
    Map<String, Lifecycle> lifecycleBeans = getLifecycleBeans();
    Map<Integer, LifecycleGroup> phases = new HashMap<>();
    // 由於onRefresh()調用時該方法時,手動設置了autoStartupOnly爲false,因此這裏的bean必需是SmartLifecycle類型而且isAutoStartup()返回true
    lifecycleBeans.forEach((beanName, bean) -> {
        if (!autoStartupOnly || (bean instanceof SmartLifecycle && ((SmartLifecycle) bean).isAutoStartup())) {
            // 獲取bean的階段值(若是沒有實現Phased接口,則值爲0)
            int phase = getPhase(bean);
            // 拿到存放該階段值的LifecycleGroup,若是爲空則新建一個並把當前階段值加入其中
            LifecycleGroup group = phases.get(phase);
            if (group == null) {
                group = new LifecycleGroup(phase, this.timeoutPerShutdownPhase, lifecycleBeans, autoStartupOnly);
                phases.put(phase, group);
            }
            group.add(beanName, bean);
        }
    });
    // 若是phases不爲空,根據階段值從小到大排序,並調用重寫Lifecycle接口的start()
    if (!phases.isEmpty()) {
        List<Integer> keys = new ArrayList<>(phases.keySet());
        Collections.sort(keys);
        for (Integer key : keys) {
            phases.get(key).start();
        }
    }
}

總結

本文主要介紹了 ApplicationContext 整個加載的流程,咱們能夠從新整理一下思路:

  1. 刷新前的準備,在這裏會記錄整個上下文啓動的開始時間,將激活標識設置爲 true,關閉標識設置爲 false
  2. 建立一個新的 BeanFactory,這裏大多數狀況下都是 DefaultListableBeanFactory。首先會檢測以前有沒有 BeanFactory,有的話會先銷燬再從新建立,而後會加載 bean 的定義元信息。
  3. 配置 BeanFactory,設置 BeanFactoryclassLoader、表達式語言處理器、添加了 ApplicationContext 新增長的 Aware 接口回調等。
  4. 調用 BeanFactory 的後置處理器,這也是 BeanFactory 的擴展點;上文有分析過這裏再也不贅述。
  5. 註冊容器內全部的 BeanPostProcessors,上文也分析過,再也不贅述;值得注意的是若是單單使用 BeanFactory 的話是不會自動註冊的。
  6. 初始化消息資源,這裏沒有過多分析,由於對咱們整個流程幾乎沒什麼影響。
  7. 初始化事件傳播器。關於 Spring 的事件,我打算後面單獨寫一篇文章來介紹,這裏就沒有多說。
  8. 在特殊的上下文環境中初始化指定的bean,模板方法留給子類實現。
  9. 註冊監聽器,這也留着到 Spring 事件中一塊兒介紹。
  10. 初始化全部非延遲加載的單例 bean,而且會回調實現了 SmartInitializingSingleton 接口的 afterSingletonsInstantiated(),這個接口算是 bean 生命週期的加強。
  11. 完成上下文的刷新,調用生命週期處理器的 onRefresh() 而且發佈上下文刷新完成事件。

最後,我模仿 Spring 寫了一個精簡版,代碼會持續更新。地址:https://github.com/leisurexi/tiny-spring

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