Spring应用上下文生命周期
Spring应用上下文生命周期整体分成四个阶段
- ConfigurableApplicationContext#refresh，加载或者刷新持久化配置
- ConfigurableApplicationContext#start，启动应用上下文
- ConfigurableApplicationContext#stop，停止应用上下文
- ConfigurableApplicationContext#close，关闭应用上下文，释放锁定资源
实际上refresh执行完成后Spring应用上下文从广义上来说已经启动了，start回调用LifeCycleProcessors的start方法，可以理解refresh处理Spring应用上下文启动需要的东西，start相当于是一个扩展，close和stop是和refresh和close类似的逆向操作。
因此Spring应用上下文生命周期重头戏是refresh和close两个方法对应的实现。
refresh-刷新应用上下文
整个refresh阶段代码如下所示:
从代码可以看出，refresh整体分为以下几个阶段:
- 准备刷新阶段: prepareRefresh
- BeanFactory创建阶段: obtainFreshBeanFactory
- BeanFactory准备阶段: prepareBeanFactory
- BeanFactory后置处理阶段: postProcessBeanFactory、invokeBeanFactoryPostProcessors
- BeanFactory注册BeanPostProcessor阶段: registerBeanPostProcessors
- 初始化内建Bean: initMessageSource、initApplicationEventMulticaster
- Spring应用上下文刷新阶段: onRefresh
- Spring事件监听器注册阶段: registerListener
- BeanFactory初始化完成阶段: finishBeanFactoryInitialization
- Spring应用上下文刷新完成阶段: finishRefresh
准备刷新阶段
prepareRefresh方法注释如下所示，可以看出，这个方法主要做了三件事来准备上下文刷新:
- 设置启动时间
- 设置激活标
- 执行任何初始化属性来源
protected void prepareRefresh() { //设置启动时间、激活标 this.startupDate = System.currentTimeMillis(); this.closed.set(false); this.active.set(true); if (logger.isDebugEnabled()) { if (logger.isTraceEnabled()) { logger.trace("Refreshing " + this); } else { logger.debug("Refreshing " + getDisplayName()); } } //初始化属性源，扩展用 initPropertySources(); //校验必要属性 getEnvironment().validateRequiredProperties(); //创建存储早期applicationListeners容器 if (this.earlyApplicationListeners == null) { this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners); } else { this.applicationListeners.clear(); this.applicationListeners.addAll(this.earlyApplicationListeners); } //创建存储早期applicationEvents容器，存储早期Spring Application事件，用于后面applicationEventMulticaster发布事件用 this.earlyApplicationEvents = new LinkedHashSet<>(); }
BeanFactory创建阶段
在AbstractRefreshableApplicationContext的refreshBeanFactory实现里，会对这个应用上下文的底层BeanFactory做一个刷新，如果之前有BeanFactory，会先停止，再初始化一个新的BeanFactory
protected final void refreshBeanFactory() throws BeansException {
//如果有BeanFactory，先关掉这个BeanFactory if (hasBeanFactory()) { destroyBeans(); closeBeanFactory(); } try {
//创建新的BeanFactory DefaultListableBeanFactory beanFactory = createBeanFactory();
//设置BeanFactory的id beanFactory.setSerializationId(getId());
//设置是否允许BeanDefinition覆盖、是否允许循环依赖 customizeBeanFactory(beanFactory);
//加载BeanDefinition loadBeanDefinitions(beanFactory);
//设置新的BeanFactory为当前应用上下文IoC容器 synchronized (this.beanFactoryMonitor) { this.beanFactory = beanFactory; } } catch (IOException ex) { throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex); } }
BeanFactory准备阶段
配置容器上下文特征，例如上下文的ClassLoader和后置处理器。
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) { //设置容器使用的类加载器: ClassLoader，默认是线程上下文类设置的加载器 beanFactory.setBeanClassLoader(getClassLoader());
//设置Bean表达式处理器，指定bean definition中的表达是值的解析策略 beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
//添加PropertyEditorRegistrar实现，存储ResourceLoader和PropertyResolver beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment())); //添加BeanPostProcessor实现，用于处理ApplicationContext的Aware回调 beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
//忽略指定接口作为依赖注入接口 beanFactory.ignoreDependencyInterface(EnvironmentAware.class); beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class); beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class); beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class); beanFactory.ignoreDependencyInterface(MessageSourceAware.class); beanFactory.ignoreDependencyInterface(ApplicationContextAware.class); //注册ResolvableDependency，这部分可以被依赖注入但不能被依赖查找 beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory); beanFactory.registerResolvableDependency(ResourceLoader.class, this); beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this); beanFactory.registerResolvableDependency(ApplicationContext.class, this); //注册ApplicationListener探测器，如果一个Bean实现了ApplicationListener接口会被当作ApplicationListener注册到Publisher beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this)); //注册动态织入后置处理器 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())); } //注册环境Bean单例对象 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()); } }
BeanFactory后置处理阶段
postProcessBeanFactory和invokeBeanFactoryPostProcessors都是Spring提供的扩展方式。
postProcessBeanFactory在AbstractApplicationContext里没有实际实现，postProcessBeanFactory注释如下:
可以看出这时Spring应用上下文内部BeanFactory已经标准初始化完成，这时所有Bean的BeanDefinition已经被加载进来，但是还没有被实例化，这时允许继承类注册特殊的BeanPostProcessors等内容。
invokeBeanFactoryPostProcessors方法注释如下:
这个方法会实例化并且执行所有被注册的BeanFactoryPostProcessor的Bean，如果给定显示顺序，按显示顺序执行，invokeBeanFactoryPostProcessors代码如下:
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
//处理BeanFactoryPostProcessors，这里细节挺多的，要按一定顺序执行BeanDefinitionRegistryPostProcessor#postProcessBeanDefinitionRegistry和BeanFactoryPostProcessor#postProcessBeanFactory PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors()); //添加LoadTimeWeaverAwareProcessor if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) { beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory)); beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader())); } }
BeanFactory注册BeanPostProcessor
registerBeanPostProcessors方法注释如下:
这个方法的作用就是实例化并且注册所有BeanPostProcessor的Bean，会按给定顺序注册。
这里注册的顺序是:
- 先注册实现PriorityOrdered的BeanPostProcessor的Bean
- 再注册实现Ordered的BeanPostProcessor的Bean
- 然后注册普通的BeanPostProcessor的Bean
- 后面注册MergedBeanDefinitionPostProcess的Bean
- 最后注册ApplicationListenerDetector的Bean
初始化内建Bean
初始化内建Bean会初始化两个Bean: MessageSource和ApplicationEventMulticaster。
这两个实现比较类似，都是判断当前BeanFactory(不判断父BeanFactory)是否包含对应Bean，如果不包含，就创建并且用registerSingleton方法注册到BeanFactory。
Spring应用上下文刷新阶段
onRefresh方法注释如下所示:
onRefresh方法是个可以被子类覆盖的模板方法，可以在实例化单例前初始化特殊的Bean。
Spring事件监听器注册阶段
registerListeners方法注释如下所示:
registerListeners方法会把实现ApplicationListener的Bean和非Bean对象注册到ApplicationEventMulticaster。
registerListeners方法代码如下:
protected void registerListeners() { //注册非Bean的ApplicationListener实现类的对象 for (ApplicationListener<?> listener : getApplicationListeners()) { getApplicationEventMulticaster().addApplicationListener(listener); } //注册ApplicationListener实现类对应的Bean String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false); for (String listenerBeanName : listenerBeanNames) { getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName); } //发送早期ApplicationEvent事件 Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents; this.earlyApplicationEvents = null; if (earlyEventsToProcess != null) { for (ApplicationEvent earlyEvent : earlyEventsToProcess) { getApplicationEventMulticaster().multicastEvent(earlyEvent); } } }
BeanFactory初始化完成阶段
finishBeanFactoryInitialization方法注释如下所示:
这个方法会结束Spring应用上下文的BeanFactory的初始化，初始化所有剩余的单例Bean。
finishBeanFactoryInitialization方法代码如下所示:
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) { //如果BeanFactory有ConversionService对象，关联到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)); } //添加StringValueResolver对象 if (!beanFactory.hasEmbeddedValueResolver()) { beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal)); } //依赖查找LoadTimeWeaverAware的Bean String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false); for (String weaverAwareName : weaverAwareNames) { getBean(weaverAwareName); } //BeanFactory临时ClassLoader置为null beanFactory.setTempClassLoader(null); //BeanFactory冻结配置 beanFactory.freezeConfiguration(); //实例化所有不是懒加载的单例对象 beanFactory.preInstantiateSingletons(); }
Spring应用上下文刷新完成阶段
finishRefresh方法注释如下所示:
finishRefresh方法结束Spring应用上下文刷新，调用LifecycleProcessor#onRefresh方法并且发送ContextRefreshedEvent。
finishRefresh方法代码如下所示:
protected void finishRefresh() { //清除ResourceLoader缓存 clearResourceCaches(); //初始化LifecycleProcessor对象 initLifecycleProcessor(); //调用LifecycleProcessor#onRefresh方法 getLifecycleProcessor().onRefresh(); //发布Spring应用上下文已刷新事件 publishEvent(new ContextRefreshedEvent(this)); //向MBeanServer托管Live Bean LiveBeansView.registerApplicationContext(this); }
start-启动应用上下文
start方法代码如下所示:
public void start() {
//启动LifecycleProcessor getLifecycleProcessor().start();
//发布应用上下文启动事件 publishEvent(new ContextStartedEvent(this)); }
stop-停止应用上下文
stop方法代码如下所示:
public void stop() {
//停止LifecycleProcessor getLifecycleProcessor().stop();
//发布应用上下文停止事件 publishEvent(new ContextStoppedEvent(this)); }
close-关闭应用上下文
protected void doClose() { //检查激活标 if (this.active.get() && this.closed.compareAndSet(false, true)) { if (logger.isDebugEnabled()) { logger.debug("Closing " + this); } //Live Bean注销托管 LiveBeansView.unregisterApplicationContext(this); try { //发布Spring应用上下文已关闭事件 publishEvent(new ContextClosedEvent(this)); } catch (Throwable ex) { logger.warn("Exception thrown from ApplicationListener handling ContextClosedEvent", ex); } //关闭LifecycleProcessor if (this.lifecycleProcessor != null) { try { this.lifecycleProcessor.onClose(); } catch (Throwable ex) { logger.warn("Exception thrown from LifecycleProcessor on context close", ex); } } //销毁Spring Bean destroyBeans(); //关闭BeanFactory closeBeanFactory(); //回调onClose onClose(); //重置本地监听者 if (this.earlyApplicationListeners != null) { this.applicationListeners.clear(); this.applicationListeners.addAll(this.earlyApplicationListeners); } //激活标设置为没激活 this.active.set(false); } }
