前面的章節介紹了SpringIoC的基礎容器BeanFactory，接下來的章節分析Spring的高階容器ApplicationContext。關於兩者的介紹，可以參考以前的章節。接下來我們以ClassPathXmlApplicationContext為例分析ApplicationContext的建立過程。

引、ApplicationContext建立過程簡析

/**
 * 建立一個新的ClassPathXmlApplicationContext容器
 * 從指定的xml檔案載入BeanDefinition並自動重新整理容器
 * @param configLocation 配置檔案位置
 * @throws BeansException 容器建立失敗，丟擲BeansException異常
 */
 

public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
    this(new String[] {configLocation}, true, null);
}

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, @Nullable ApplicationContext parent) throws BeansException {
    // 呼叫父類構造器
    super
 
(parent);
    // 設定配置檔案路徑
    setConfigLocations(configLocations);
    if (refresh) {
        // 擴充套件功能
        refresh();
    }
}

public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
        // 1、準備重新整理上下文環境
        prepareRefresh();
        // 2、讀取xml並初始化BeanFactory
 

        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
        // 3、填充BeanFactory功能
        prepareBeanFactory(beanFactory);
        try {
            // 4、子類覆蓋方法額外處理(空方法)
            postProcessBeanFactory(beanFactory);
            // 5、調動BeanFactoryPostProcessor
            invokeBeanFactoryPostProcessors(beanFactory);
            // 6、註冊BeanPostProcessors
            registerBeanPostProcessors(beanFactory);
            // 7、初始化Message資源
            initMessageSource();
            // 8、初始事件廣播器
            initApplicationEventMulticaster();
            // 9、留給子類初始化其他Bean(空的模板方法)
            onRefresh();
            // 10、註冊事件監聽器
            registerListeners();
            // 11、初始化其他的單例Bean(非延遲載入的)
            finishBeanFactoryInitialization(beanFactory);
            // 12、完成重新整理過程,通知生命週期處理器lifecycleProcessor重新整理過程,同時發出ContextRefreshEvent通知
            finishRefresh();
        }
        catch (BeansException ex) {
            // 13、銷燬已經建立的Bean
            destroyBeans();
            // 14、重置容器啟用標籤
            cancelRefresh(ex);
            throw ex;
        }
        finally {
            resetCommonCaches();
        }
    }
}

逐步分析refresh()方法。

1、prepareRefresh重新整理上下文的準備工作

/**
 * 準備重新整理上下文環境，設定它的啟動日期和活動標誌，以及執行任何屬性源的初始化。
 * Prepare this context for refreshing, setting its startup date and
 * active flag as well as performing any initialization of property sources.
 */
protected void prepareRefresh() {
    this.startupDate = System.currentTimeMillis();
    this.closed.set(false);
    this.active.set(true);

    // 在上下文環境中初始化任何佔位符屬性源。(空的方法,留給子類覆蓋)
    initPropertySources();

    // 驗證需要的屬性檔案是否都已放入環境中
    getEnvironment().validateRequiredProperties();

    // 允許收集早期的應用程式事件，一旦有了多播器，就可以釋出……
    this.earlyApplicationEvents = new LinkedHashSet<>();
}

2、obtainFreshBeanFactory->讀取xml並初始化BeanFactory

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
    // 重新整理BeanFactory並返回BeanFactory物件
    refreshBeanFactory();
    return getBeanFactory();
}

protected final void refreshBeanFactory() throws BeansException {
    // 1、如果BeanFactory的例項已經存在,則銷燬並關閉
    if (hasBeanFactory()) {
        destroyBeans();
        closeBeanFactory();
    }
    // 2、重新建立BeanFactory
    try {
        // 建立BeanFactory
        DefaultListableBeanFactory beanFactory = createBeanFactory();
        // 為BeanFactory設定id
        beanFactory.setSerializationId(getId());
        // 定製beanFactory
        customizeBeanFactory(beanFactory);
        // 載入BeanDefinition
        loadBeanDefinitions(beanFactory);
        synchronized (this.beanFactoryMonitor) {
            this.beanFactory = beanFactory;
        }
    }
    catch (IOException ex) {
        throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
    }
}

該方法的主要作用就是保證獲取一個全新的beanFactory，關於beanFactory我們在前面已經做了很多介紹了，這裡不在說明。

3、prepareBeanFactory–>填充BeanFactory功能

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
    // Tell the internal bean factory to use the context's class loader etc.
    // 設定beanFactory的classLoader
    beanFactory.setBeanClassLoader(getClassLoader());
    // 設定beanFactory的表示式語言處理器,Spring3開始增加了對語言表示式的支援,預設可以使用#{bean.xxx}的形式來呼叫相關屬性值
    beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
    // 為beanFactory增加一個預設的propertyEditor,這個主要是對bean的屬性等設定管理的一個工具
    beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

    // Configure the bean factory with context callbacks.
    // 新增ApplicationContextAwareProcessor
    beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

    // 設定忽略自動裝配的介面
    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.
    // 設定幾個自動裝配的特殊規則
    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.
    beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

    // Detect a LoadTimeWeaver and prepare for weaving, if found.
    // 增加對AspectJ的支援
    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.
    // 註冊預設的系統環境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());
    }
}

4、postProcessBeanFactory

該方法是個空的模板方法。

5、invokeBeanFactoryPostProcessors–>呼叫BeanFactoryPostProcessor

BeanFactoryPostProcessor在Spring中非常重要，詳細分析其呼叫過程。

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    //getBeanFactoryPostProcessors->獲取註冊的BeanFactoryPostProcessor
    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()));
    }
}

通過PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());獲取註冊的BeanFactoryPostProcessor並呼叫。

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

    // Invoke BeanDefinitionRegistryPostProcessors first, if any.
    // 1、首先呼叫BeanDefinitionRegistryPostProcessors
    Set<String> processedBeans = new HashSet<>();

    // beanFactory是BeanDefinitionRegistry型別
    if (beanFactory instanceof BeanDefinitionRegistry) {
        BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
        // 定義BeanFactoryPostProcessor
        List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
        // 定義BeanDefinitionRegistryPostProcessor集合
        List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();

        // 迴圈手動註冊的beanFactoryPostProcessors
        for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
            // 如果是BeanDefinitionRegistryPostProcessor的例項話,則呼叫其postProcessBeanDefinitionRegistry方法,對bean進行註冊操作
            if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                // 如果是BeanDefinitionRegistryPostProcessor型別,則直接呼叫其postProcessBeanDefinitionRegistry
                BeanDefinitionRegistryPostProcessor registryProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor;
                registryProcessor.postProcessBeanDefinitionRegistry(registry);
                registryProcessors.add(registryProcessor);
            }
            // 否則則將其當做普通的BeanFactoryPostProcessor處理,直接加入regularPostProcessors集合,以備後續處理
            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.
        // 首先呼叫實現了PriorityOrdered(有限排序介面)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);
        // 加入registryProcessors集合
        registryProcessors.addAll(currentRegistryProcessors);
        // 呼叫所有實現了PriorityOrdered的的BeanDefinitionRegistryPostProcessors的postProcessBeanDefinitionRegistry方法,註冊bean
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        // 清空currentRegistryProcessors,以備下次使用
        currentRegistryProcessors.clear();

        // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
        // 其次,呼叫實現了Ordered(普通排序介面)的BeanDefinitionRegistryPostProcessors
        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);
            }
        }
        // 排序
        sortPostProcessors(currentRegistryProcessors, beanFactory);
        // 加入registryProcessors集合
        registryProcessors.addAll(currentRegistryProcessors);
        // 呼叫所有實現了PriorityOrdered的的BeanDefinitionRegistryPostProcessors的postProcessBeanDefinitionRegistry方法,註冊bean
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        // 清空currentRegistryProcessors,以備下次使用
        currentRegistryProcessors.clear();

        // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
        // 最後,呼叫其他的BeanDefinitionRegistryPostProcessors
        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;
                }
            }
            // 排序
            sortPostProcessors(currentRegistryProcessors, beanFactory);
            // 加入registryProcessors集合
            registryProcessors.addAll(currentRegistryProcessors);
            // 呼叫其他的BeanDefinitionRegistryPostProcessors的postProcessBeanDefinitionRegistry方法,註冊bean
            invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
            // 清空currentRegistryProcessors,以備下次使用
            currentRegistryProcessors.clear();
        }

        // Now, invoke the postProcessBeanFactory callback of all processors handled so far.
        // 呼叫所有BeanDefinitionRegistryPostProcessor(包括手動註冊和通過配置檔案註冊)
        // 和BeanFactoryPostProcessor(只有手動註冊)的回撥函式-->postProcessBeanFactory
        invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
        invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
    }

    // 2、如果不是BeanDefinitionRegistry的例項,那麼直接呼叫其回撥函式即可-->postProcessBeanFactory
    else {
        // Invoke factory processors registered with the context instance.
        invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
    }

    // Do not initialize FactoryBeans here: We need to leave all regular beans
    // uninitialized to let the bean factory post-processors apply to them!
    // 3、上面的程式碼已經處理完了所有的BeanDefinitionRegistryPostProcessors和手動註冊的BeanFactoryPostProcessor
    // 接下來要處理通過配置檔案註冊的BeanFactoryPostProcessor
    // 首先獲取所有的BeanFactoryPostProcessor(注意:這裡獲取的集合會包含BeanDefinitionRegistryPostProcessors)
    String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

    // Separate between BeanFactoryPostProcessors that implement PriorityOrdered, Ordered, and the rest.
    // 這裡,將實現了PriorityOrdered,Ordered的處理器和其他的處理器區分開來,分別進行處理
    // PriorityOrdered有序處理器
    List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
    // Ordered有序處理器
    List<String> orderedPostProcessorNames = new ArrayList<>();
    // 無序處理器
    List<String> nonOrderedPostProcessorNames = new ArrayList<>();
    for (String ppName : postProcessorNames) {
        // 判斷processedBeans是否包含當前處理器(processedBeans中的處理器已經被處理過);如果包含,則不做任何處理
        if (processedBeans.contains(ppName)) {
            // skip - already processed in first phase above
        }
        else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
            // 加入到PriorityOrdered有序處理器集合
            priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
        }
        else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
            // 加入到Ordered有序處理器集合
            orderedPostProcessorNames.add(ppName);
        }
        else {
            // 加入到無序處理器集合
            nonOrderedPostProcessorNames.add(ppName);
        }
    }

    // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
    // 首先呼叫實現了PriorityOrdered介面的處理器
    sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

    // Next, invoke the BeanFactoryPostProcessors that implement Ordered.
    // 其次,呼叫實現了Ordered介面的處理器
    List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>();
    for (String postProcessorName : orderedPostProcessorNames) {
        orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    sortPostProcessors(orderedPostProcessors, beanFactory);
    invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

    // Finally, invoke all other BeanFactoryPostProcessors.
    // 最後,呼叫無序處理器
    List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
    for (String postProcessorName : nonOrderedPostProcessorNames) {
        nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }