Spring AbstractApplicationContext抽象类的refresh()方法--笔记
Spring中AbstractApplicationContext抽象类的refresh()方法是用来刷新Spring的应用上下文的。下面Spring的应用上下文我都叫作context
@Override public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. prepareRefresh();//一 // Tell the subclass to refresh the internal bean factory. ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();//二、 // Prepare the bean factory for use in this context. prepareBeanFactory(beanFactory);//三、 try { // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory);//四、 // Invoke factory processors registered as beans in the context. invokeBeanFactoryPostProcessors(beanFactory);//五、 // Register bean processors that intercept bean creation. registerBeanPostProcessors(beanFactory);//六、 // Initialize message source for this context. initMessageSource();//七、 // Initialize event multicaster for this context. initApplicationEventMulticaster();//八、 // Initialize other special beans in specific context subclasses. onRefresh();//九、 // Check for listener beans and register them. registerListeners();//十、 // Instantiate all remaining (non-lazy-init) singletons. finishBeanFactoryInitialization(beanFactory);//十一、 // Last step: publish corresponding event. finishRefresh();//十二、 } 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();//如果刷新失败那么就会将已经创建好的单例Bean销毁掉 // Reset 'active' flag. cancelRefresh(ex);//重置context的活动状态 // Propagate exception to caller. throw ex;//抛出异常 } finally { // Reset common introspection caches in Spring's core, since we // might not ever need metadata for singleton beans anymore... resetCommonCaches();//重置的Spring内核的缓存。因为可能不再需要metadata给单例Bean了。 } } }
这个方法的每一行代码都很重要。已经在代码中标上序号，下面会一句一句来解释。
一、prePareRefresh()
①、这个方法设置context的启动日期。
②、设置context当前的状态，是活动状态还是关闭状态。
③、初始化context environment（上下文环境）中的占位符属性来源。
④、验证所有必需的属性。
二、ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
让这个类（AbstractApplicationContext）的子类刷新内部bean工厂。实际上就是重新创建一个bean工厂。
obtainFreshBeanFactory()方法的代码如下：
/** * Tell the subclass to refresh the internal bean factory. * @return the fresh BeanFactory instance * @see #refreshBeanFactory() * @see #getBeanFactory() */ protected ConfigurableListableBeanFactory obtainFreshBeanFactory() { refreshBeanFactory();//真正的刷新bean工厂。 ConfigurableListableBeanFactory beanFactory = getBeanFactory(); if (logger.isDebugEnabled()) { logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory); } return beanFactory; }
上述代码中标红的refreshBeanFactory()最重要，其具体代码如下：
/** * This implementation performs an actual refresh of this context's underlying * bean factory, shutting down the previous bean factory (if any) and * initializing a fresh bean factory for the next phase of the context's lifecycle. */ @Override protected final void refreshBeanFactory() throws BeansException { if (hasBeanFactory()) {//如果已经存在一个bean工厂那么就将其销毁，关闭。 destroyBeans(); closeBeanFactory(); } try { DefaultListableBeanFactory beanFactory = createBeanFactory();//新建一个Bean工厂。 beanFactory.setSerializationId(getId()); customizeBeanFactory(beanFactory);//自定义bean工厂。 loadBeanDefinitions(beanFactory);//加载BeanDefinition synchronized (this.beanFactoryMonitor) { this.beanFactory = beanFactory;//将创建好的bean工厂的引用交给的context来管理。 } } catch (IOException ex) {//加载bean定义资源的时候可能会抛出异常。 throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex); } }
三、prepareBeanFactory(beanFactory);
上一步已经把工厂建好了，但是还不能投入使用，因为工厂里什么都没有，还需要配置一些东西。看看这个方法的注释
他说配置这个工厂的标准环境，比如context的类加载器和后处理器。看看具体有哪些，反正很多。都是往BeanFactory中add什么东西，或者Register什么东西。反正在一系列的add和Register后工厂的功能会越来越健全。
直接贴代码：prepareBeanFactory(ConfigurableListableBeanFactory beanFactory)
/** * Configure the factory's standard context characteristics, * such as the context's ClassLoader and post-processors. * @param beanFactory the BeanFactory to configure */ protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) { // Tell the internal bean factory to use the context's class loader etc. beanFactory.setBeanClassLoader(getClassLoader()); beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader())); beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment())); // Configure the bean factory with context callbacks. beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this)); 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. 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. 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. 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()); } }
四、postProcessBeanFactory(beanFactory);
上面对bean工厂进行了许多配置，现在需要对bean工厂进行一些处理。
①、添加一个ServletContextAwareProcessor到bean工厂中。
②、在bean工厂自动装配的时候忽略一些接口。如：ServletContextAware、ServletConfigAware
③、注册WEB应用特定的域（scope）到bean工厂中，以便WebApplicationContext可以使用它们。比如"request", "session", "globalSession", "application"，
④、注册WEB应用特定的Environment bean到bean工厂中，以便WebApplicationContext可以使用它们。如："contextParameters", "contextAttributes"
下面是这个方法的代码：
/** * Register request/session scopes, a {@link ServletContextAwareProcessor}, etc. */ @Override 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); }
五、invokeBeanFactoryPostProcessors(beanFactory)
这一步也是对bean工厂进行一些处理。这一步主要是调用所有的bean工厂处理器（BeanFactoryPostProcessor）对bean工厂进行一些处理。这个方法必须在所有的singleton初始化之前调用。
/** * Instantiate and invoke all registered BeanFactoryPostProcessor beans, * respecting explicit order if given. * <p>Must be called before singleton instantiation. */ protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) { PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());//这个行代码重要 // 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())); } }
上面标红的代码的具体实现如下，代码非常多。主要是在这里面调用了所有的BeanFactoryPostProcessor。
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> registryPostProcessors = new LinkedList<BeanDefinitionRegistryPostProcessor>(); for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) { if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) { BeanDefinitionRegistryPostProcessor registryPostProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor; registryPostProcessor.postProcessBeanDefinitionRegistry(registry); registryPostProcessors.add(registryPostProcessor); } 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. String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered. List<BeanDefinitionRegistryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>(); for (String ppName : postProcessorNames) { if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); processedBeans.add(ppName); } } sortPostProcessors(beanFactory, priorityOrderedPostProcessors); registryPostProcessors.addAll(priorityOrderedPostProcessors); invokeBeanDefinitionRegistryPostProcessors(priorityOrderedPostProcessors, registry); // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered. postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); List<BeanDefinitionRegistryPostProcessor> orderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>(); for (String ppName : postProcessorNames) { if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) { orderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); processedBeans.add(ppName); } } sortPostProcessors(beanFactory, orderedPostProcessors); registryPostProcessors.addAll(orderedPostProcessors); invokeBeanDefinitionRegistryPostProcessors(orderedPostProcessors, registry); // 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)) { BeanDefinitionRegistryPostProcessor pp = beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class); registryPostProcessors.add(pp); processedBeans.add(ppName); pp.postProcessBeanDefinitionRegistry(registry); reiterate = true; } } } // Now, invoke the postProcessBeanFactory callback of all processors handled so far. invokeBeanFactoryPostProcessors(registryPostProcessors, 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(beanFactory, priorityOrderedPostProcessors); 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(beanFactory, orderedPostProcessors); 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(); }
六、registerBeanPostProcessors(beanFactory);
注册用来拦截bean创建的BeanPostProcessor bean.这个方法需要在所有的application bean初始化之前调用。把这个注册的任务委托给了PostProcessorRegistrationDelegate来完成。
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.首先，注册实现了PriorityOrdered接口的BeanPostProcessor sortPostProcessors(beanFactory, priorityOrderedPostProcessors); registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors); // Next, register the BeanPostProcessors that implement Ordered.然后注册实现了Ordered接口的BeanPostProcessor 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(beanFactory, orderedPostProcessors); registerBeanPostProcessors(beanFactory, orderedPostProcessors); // Now, register all regular BeanPostProcessors.注册所有常规的的BeanPostProcessor 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.最后重新注册所有的内部BeanPostProcessor sortPostProcessors(beanFactory, internalPostProcessors); registerBeanPostProcessors(beanFactory, internalPostProcessors); // Re-register post-processor for detecting inner beans as ApplicationListeners,重新注册用来自动探测内部ApplicationListener的post-processor，这样可以将他们移到处理器链条的末尾。 // moving it to the end of the processor chain (for picking up proxies etc). beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext)); }
七、initMessageSource();
初始化MessageSource接口的一个实现类。这个接口提供了消息处理功能。主要用于国际化/i18n。
八、initApplicationEventMulticaster();
为这个context初始化一个事件广播器（ApplicationEventMulticaster）。
AbstractApplicationContext中有一个常量：
/** * Name of the ApplicationEventMulticaster bean in the factory. * If none is supplied, a default SimpleApplicationEventMulticaster is used. * @see org.springframework.context.event.ApplicationEventMulticaster * @see org.springframework.context.event.SimpleApplicationEventMulticaster */ public static final String APPLICATION_EVENT_MULTICASTER_BEAN_NAME = "applicationEventMulticaster";
这个常量就是的ApplicationEventMulticaster bean的名字。程序首先会检查bean工厂中是否有bean的名字和这个常量相同的，如果没有则说明没有那么就使用默认的ApplicationEventMulticaster 的实现：SimpleApplicationEventMulticaster
/** * Initialize the ApplicationEventMulticaster. * Uses SimpleApplicationEventMulticaster if none defined in the context. * @see org.springframework.context.event.SimpleApplicationEventMulticaster */ protected void initApplicationEventMulticaster() { ConfigurableListableBeanFactory beanFactory = getBeanFactory(); if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {检查是否给context配了一个ApplicationEventMulticaster实现类 this.applicationEventMulticaster = beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class); if (logger.isDebugEnabled()) { logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]"); } } else {//如果没有，就是用默认的实现类 SimpleApplicationEventMulticaster 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 + "]"); } } }
九、onRefresh();
在AbstractApplicationContext的子类中初始化其他特殊的bean。其实就是初始化ThemeSource接口的实例。这个方法需要在所有单例bean初始化之前调用。
十、registerListeners();
注册应用的监听器。就是注册实现了ApplicationListener接口的监听器bean，这些监听器是注册到ApplicationEventMulticaster中的。这不会影响到其它监听器bean。在注册完以后，还会将其前期的事件发布给相匹配的监听器。
/** * Add beans that implement ApplicationListener as listeners. * Doesn't affect other listeners, which can be added without being beans. */ 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...至此，已经完成将监听器注册到ApplicationEventMulticaster中，下面将发布前期的事件给监听器。 Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents; this.earlyApplicationEvents = null; if (earlyEventsToProcess != null) { for (ApplicationEvent earlyEvent : earlyEventsToProcess) { getApplicationEventMulticaster().multicastEvent(earlyEvent); } } }
十一、finishBeanFactoryInitialization(beanFactory);
完成bean工厂的初始化工作。这一步非常复杂，也非常重要，涉及到了bean的创建。第二步中只是完成了BeanDefinition的定义、解析、处理、注册。但是还没有初始化bean实例。这一步将初始化所有非懒加载的单例bean。这一步将会重新在一篇新的笔记中介绍。
十二、finishRefresh();
完成context的刷新。主要是调用LifecycleProcessor的onRefresh()方法，并且发布事件（ContextRefreshedEvent）。