【spring 源碼】IOC 之 ClassPathXmlApplicationContext

先看下啓動 Spring 容器的一個例子:前端

public class App {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("classpath:application.xml");
        // 從 context 中取出咱們的 Bean
        MessageService messageService = context.getBean(MessageService.class);
        System.out.println(messageService.getMessage());
    }
}
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ClassPathXmlApplicationContext 的源碼:

public class ClassPathXmlApplicationContext extends AbstractXmlApplicationContext {
  // 將配置文件做爲資源都存放到這個數組中
  private Resource[] configResources;
 
 // 若是已經有 ApplicationContext並須要配置成父子關係,那麼調用這個構造方法
  public ClassPathXmlApplicationContext(ApplicationContext parent) {
    super(parent);
  }
  ...
  public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) throws BeansException {
    super(parent);
    // 解析配置文件列表,放置到上面說的那個 configResources 數組中
    setConfigLocations(configLocations);
    if (refresh) {
      refresh(); // 核心方法 調用AbstractApplicationContext.refresh()
    }
  }
    ...
}
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// AbstractApplicationContext.java L509java

@Override
public void refresh() throws BeansException, IllegalStateException {
   synchronized (this.startupShutdownMonitor) {
       // 準備工做,記錄下容器的啓動時間、標記「已啓動」狀態、處理配置文件中的佔位符
      prepareRefresh();
       // 這步比較關鍵,這步完成後,配置文件就會解析成一個個 Bean 定義,註冊到 BeanFactory 中,這裏的 Bean 尚未初始化,只是配置信息都提取出來了,
      // 註冊也只是將這些信息都保存到了註冊中心(說到底核心是一個 beanName-> beanDefinition 的 map)
      ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
 
      // 設置 BeanFactory 的類加載器,添加幾個 BeanPostProcessor,手動註冊幾個特殊的 bean
      // 這塊待會會展開說
      prepareBeanFactory(beanFactory);
 
      try {
         // 【這裏須要知道 BeanFactoryPostProcessor 這個知識點,Bean 若是實現了此接口,那麼在容器初始化之後,Spring 會負責調用裏面的 postProcessBeanFactory 方法。】
 
         // 這裏是提供給子類的擴展點,到這裏的時候,全部的 Bean 都加載、註冊完成了,可是都尚未初始化
         // 具體的子類能夠在這步的時候添加一些特殊的BeanFactoryPostProcessor 的實現類或作點什麼事
         postProcessBeanFactory(beanFactory);
         // 調用 BeanFactoryPostProcessor 各個實現類的 postProcessBeanFactory(factory) 方法
         invokeBeanFactoryPostProcessors(beanFactory);
 
         // 註冊 BeanPostProcessor 的實現類,注意看和 BeanFactoryPostProcessor 的區別
         // 此接口兩個方法: postProcessBeforeInitialization 和 postProcessAfterInitialization
         // 兩個方法分別在 Bean 初始化以前和初始化以後獲得執行。注意,到這裏 Bean 還沒初始化
         registerBeanPostProcessors(beanFactory);
 
         // 初始化當前 ApplicationContext 的 MessageSource(國際化相關信息),國際化這裏就不展開說了
         initMessageSource();
          // 初始化當前 ApplicationContext 的事件廣播器,這裏也不展開了
         initApplicationEventMulticaster();
 
         // 從方法名就能夠知道,典型的模板方法(鉤子方法),
         // 具體的子類能夠在這裏初始化一些特殊的 Bean(在初始化 singleton beans 以前)
         onRefresh();
 
         // 註冊事件監聽器,監聽器須要實現 ApplicationListener 接口。這也不是咱們的重點,過
         registerListeners();
 
         // 重點,重點,重點
         // 初始化全部的 singleton beans
         //(lazy-init 的除外)
         finishBeanFactoryInitialization(beanFactory);
 
         // 最後,廣播事件,ApplicationContext 初始化完成
         finishRefresh();
      } catch (BeansException ex) {
         
         // Destroy already created singletons to avoid dangling resources.
         // 銷燬已經初始化的 singleton 的 Beans,以避免有些 bean 會一直佔用資源
         destroyBeans();
          // Reset 'active' flag.
         cancelRefresh(ex);
          // 把異常往外拋
         throw ex;
      }finally {
         // Reset common introspection caches in Spring's core, since we // might not ever need metadata for singleton beans anymore... resetCommonCaches(); } } } 複製代碼

接下來對refresh()方法進行分析:web

1-0.prepareRefresh() 建立 Bean 容器前的準備工做

AbstractApplicationContext.java L557spring

protected void prepareRefresh() {
   // 將 active 屬性設置爲 true,closed 屬性設置爲 false,它們都是 AtomicBoolean 類型
   this.closed.set(false);
   this.active.set(true);
    // Initialize any placeholder property sources in the context environment
   initPropertySources();
    // 校驗 xml 配置文件
   getEnvironment().validateRequiredProperties();
    this.earlyApplicationEvents = new LinkedHashSet<ApplicationEvent>();
}
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1-1.obtainFreshBeanFactory() 建立 Bean 容器,加載並註冊 Bean

// AbstractApplicationContext.java L613後端

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
   // 關閉舊的 BeanFactory (若是有),建立新的 BeanFactory,加載 Bean 定義、註冊 Bean 等等
   refreshBeanFactory();
   // 返回剛剛建立的 BeanFactory
   ConfigurableListableBeanFactory beanFactory = getBeanFactory();
   if (logger.isDebugEnabled()) {
      logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
   }
   return beanFactory;
}
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refreshBeanFactory()是建立bean的入口,並將bean實例放到bean工廠的入口(beanName爲key,bean實例爲value放入beanFactory裏的map中),在《【spring 源碼】IOC 之bean實例的建立》裏詳細介紹這個方法的實現。數組

1-2 prepareBeanFactory(beanFactory) 準備bean容器

AbstractApplicationContext.java L627bash

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
		// 設置 BeanFactory 的類加載器,咱們知道 BeanFactory 須要加載類,也就須要類加載器,這裏設置爲當前線程的上下文類加載器
		beanFactory.setBeanClassLoader(getClassLoader());
		//設置spring 的Spel表達式相關解析器,不是主流程,不作拓展
		beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
		//設置PropertyEditorRegistrar,經過PropertyEditor將xml解析出來的bean屬性(字符串)和相應的java類型作轉換
		beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

		// 添加一個 BeanPostProcessor,這個 processor 比較簡單,
        // 實現了 Aware 接口的幾個特殊的 beans 在初始化的時候,這個 processor 負責回調
		beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
		 // 下面幾行的意思就是,若是某個 bean 依賴於如下幾個接口的實現類,在自動裝配的時候忽略它們,Spring 會經過其餘方式來處理這些依賴。
		beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
		beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
		beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
		beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
		beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
		beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

		  /**
            * 下面幾行就是爲特殊的幾個 bean 賦值,若是有 bean 依賴瞭如下幾個,會注入這邊相應的值,
            * 以前咱們說過,"當前 ApplicationContext 持有一個 BeanFactory",這裏解釋了第一行
            * ApplicationContext 繼承了 ResourceLoader、ApplicationEventPublisher、MessageSource
            * 因此對於這幾個,能夠賦值爲 this,注意 this 是一個 ApplicationContext
            */
		beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
		beanFactory.registerResolvableDependency(ResourceLoader.class, this);
		beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
		beanFactory.registerResolvableDependency(ApplicationContext.class, this);

		// ,在 bean 實例化後,若是是 ApplicationListener 的子類,那麼將其添加到 listener 列表中,能夠理解成:註冊事件監聽器
		beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

		// 這裏涉及到特殊的 bean:loadTimeWeaver,織入的一種方式,此處這不是咱們的重點,忽略它
		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()));
		}

        /**
        * 從下面幾行代碼咱們能夠知道,Spring 每每很 "智能" 就是由於它會幫咱們默認註冊一些有用的 bean,
        * 咱們也能夠選擇覆蓋
        */
		//註冊一個默認的environment的bean
		if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
			beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
		}
		//註冊一個systemProperties的bean
		if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
			beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
		}
		//註冊一個systemEnvironment的bean
		if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
			beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
		}
	}
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至此,準備bean容器結束了,主要就是初始化bean工廠的一些環境、類加載器等session

1-3 postProcessBeanFactory(beanFactory)

主要做用是:承接前文中的prepareBeanFactory()方法後,供子類在標準的基礎上再添加自定義的屬性性質,主要是註冊BeanPostProcessors //AbstractRefreshableWebApplicationContext.java L159mybatis

/**
	 * Register request/session scopes, a {@link ServletContextAwareProcessor}, etc.
	 */
	@Override
	protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
	    //註冊ServletContextAwareProcessor
		beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext, this.servletConfig));
		beanFactory.ignoreDependencyInterface(ServletContextAware.class);
		beanFactory.ignoreDependencyInterface(ServletConfigAware.class);
        
        //註冊web環境,包括request、session、golableSession、application
		WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext);
		  //註冊servletContext、contextParamters、contextAttributes、servletConfig單例bean
		WebApplicationContextUtils.registerEnvironmentBeans(beanFactory, this.servletContext, this.servletConfig);
	}
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1-4 invokeBeanFactoryPostProcessors(beanFactory)

主要是實例化和調用全部已註冊的BeanFactoryPostProcessors的postProcessBeanFactory(factory) 方法 //AbstractApplicationContext.java L686app

/**
	 * Instantiate and invoke all registered BeanFactoryPostProcessor beans,
	 * respecting explicit order if given.
	 * <p>Must be called before singleton instantiation.
	 */
	protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
	    //經過一個委託類來處理實例化調用
		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()));
		}
	}
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1-4-0 invokeBeanFactoryPostProcessors(beanFactory,beanFactoryPostProcessors)

//PostProcessorRegistrationDelegate.java L52

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

		// Invoke BeanDefinitionRegistryPostProcessors first, if any.
		Set<String> processedBeans = new HashSet<String>();

		if (beanFactory instanceof BeanDefinitionRegistry) {
			BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
			List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
			List<BeanDefinitionRegistryPostProcessor> registryProcessors = new LinkedList<BeanDefinitionRegistryPostProcessor>();
            //遍歷BeanFactoryPostProcessors
			for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
				if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
				//BeanDefinitionRegistryPostProcessor這個類很重要,spring集成mybatis時會用到它。後面會有篇文章專門介紹它的做用
				//BeanDefinitionRegistryPostProcessor容許在正常的BeanFactoryPostProcessor檢測開始以前註冊更多的自定義bean。常常用來自定義註解
					BeanDefinitionRegistryPostProcessor registryProcessor =
							(BeanDefinitionRegistryPostProcessor) postProcessor;
					registryProcessor.postProcessBeanDefinitionRegistry(registry);
					registryProcessors.add(registryProcessor);
				}
				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<BeanDefinitionRegistryPostProcessor>();

			// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
			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);
				}
			}
			sortPostProcessors(currentRegistryProcessors, beanFactory);
			registryProcessors.addAll(currentRegistryProcessors);
			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
			currentRegistryProcessors.clear();

			// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
			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.
			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();
			}

			// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
			invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
			invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
		}

		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!
		String[] postProcessorNames =
				beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

		// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
		// Ordered, and the rest.
		List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
		List<String> orderedPostProcessorNames = new ArrayList<String>();
		List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
		for (String ppName : postProcessorNames) {
			if (processedBeans.contains(ppName)) {
				// 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.
		sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
		invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

		// Next, invoke the BeanFactoryPostProcessors that implement 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.
		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();
	}
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咱們來總結一下,到目前爲止,應該說 BeanFactory 已經建立完成,而且全部的實現了 BeanFactoryPostProcessor 接口的 Bean 都已經初始化而且其中的 postProcessBeanFactory(factory) 方法已經獲得執行了。全部實現了 BeanPostProcessor 接口的 Bean 也都完成了初始化。

1-5 finishBeanFactoryInitialization(beanFactory)

初始化全部的 singleton beans

/**
	 * Finish the initialization of this context's bean factory, * initializing all remaining singleton beans. */ protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) { // 首先,初始化名字爲 conversionService 的 Bean // 注意了,初始化的動做包裝在 beanFactory.getBean(...) 中 //conversionService這個類相信用過的人不會陌生,它用來將前端傳過來的參數和後端的 controller 方法上的參數進行綁定的時候用。像前端傳過來的字符串、整數要轉換爲後端的 String、Integer 很容易,可是若是 controller 方法須要的是一個枚舉值,或者是 Date 這些非基礎類型(含基礎類型包裝類)值的時候,咱們就能夠考慮採用 ConversionService 來進行轉換 if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) && beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) { beanFactory.setConversionService( //beanFactory.getBean(),是bean真正初始化過程的關鍵入口 beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)); } // Register a default embedded value resolver if no bean post-processor // (such as a PropertyPlaceholderConfigurer bean) registered any before: // at this point, primarily for resolution in annotation attribute values. if (!beanFactory.hasEmbeddedValueResolver()) { beanFactory.addEmbeddedValueResolver(new StringValueResolver() { @Override public String resolveStringValue(String strVal) { return getEnvironment().resolvePlaceholders(strVal); } }); } // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early. String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false); for (String weaverAwareName : weaverAwareNames) { getBean(weaverAwareName); } // Stop using the temporary ClassLoader for type matching. beanFactory.setTempClassLoader(null); // Allow for caching all bean definition metadata, not expecting further changes. beanFactory.freezeConfiguration(); // 開始初始化剩下的 beanFactory.preInstantiateSingletons(); } 複製代碼

從上面最後一行往裏看,咱們又回到 DefaultListableBeanFactory#preInstantiateSingletons了 //DefaultListableBeanFactory.java L728

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

		for (String beanName : beanNames) {
		    //合併父bean中的配置   
			RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
			if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
				if (isFactoryBean(beanName)) {
    				// FactoryBean 的話,在 beanName 前面加上 ‘&’ 符號。再調用 getBean
					final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
					boolean isEagerInit;
					// 判斷當前 FactoryBean 是不是 SmartFactoryBean 的實現,此處忽略,直接跳過
					if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
						isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
							@Override
							public Boolean run() {
								return ((SmartFactoryBean<?>) factory).isEagerInit();
							}
						}, getAccessControlContext());
					}
					else {
						isEagerInit = (factory instanceof SmartFactoryBean &&
								((SmartFactoryBean<?>) factory).isEagerInit());
					}
					if (isEagerInit) {
						getBean(beanName);
					}
				}
				else {
				    // 對於普通的 Bean,只要調用 getBean(beanName) 這個方法就能夠進行初始化了
					getBean(beanName);
				}
			}
		}

		// 到這裏說明全部的非懶加載的 singleton beans 已經完成了初始化
       // 若是咱們定義的 bean 是實現了 SmartInitializingSingleton 接口的,那麼在這裏獲得回調,忽略
		for (String beanName : beanNames) {
			Object singletonInstance = getSingleton(beanName);
			if (singletonInstance instanceof SmartInitializingSingleton) {
				final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
				if (System.getSecurityManager() != null) {
					AccessController.doPrivileged(new PrivilegedAction<Object>() {
						@Override
						public Object run() {
							smartSingleton.afterSingletonsInstantiated();
							return null;
						}
					}, getAccessControlContext());
				}
				else {
					smartSingleton.afterSingletonsInstantiated();
				}
			}
		}
	}
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上面代碼裏屢次出現getBean() 方法,這個方法咱們常常用來從 BeanFactory 中獲取一個 Bean,而初始化的過程也封裝到了這個方法裏,詳見 【spring 源碼】IOC 之 bean實例初始化

(未完,待續)

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