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
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 BeanFactory
和 ApplicationContext
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。ApplicationContext
是 BeanFactory
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:
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
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
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<>(); }
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(); }
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... }
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; } }
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()); } }
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())); } }
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 BeanDefinitionRegistryPostProcessor
和 BeanFactoryPostProcessor
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
爲 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; }
BeanDefinitionRegistryPostProcessor
比 BeanFactoryPostProcessor
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。
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 BeanPostProcessors
的 bean
,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。
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(); }
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()
在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。
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); }
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); } }
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(); } } }
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:
true
,關閉標識設置爲 false
。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。BeanFactory
,設置 BeanFactory
的 classLoader
、表達式語言處理器、添加了 ApplicationContext
新增長的 Aware
接口回調等。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。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。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。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。