Spring中bean的生命周期 要想讲清楚spring中bean的生命周期，真的是不容易，以AnnotationConfigApplicationContext上下文为基础来讲解bean的生命周期，AnnotationConfigApplicationContext是基于注解的上下文，使用XML的方式现在很少见，所以以此上下文为基础，使用XML的上下文ClassPathXmlApplicationContext的步骤和AnnotationConfigApplicationContext类似。
【Spring中bean的生命周期之getSingleton方法】了解过spring源码的都知道，在AnnotationConfigApplicationContext中调用了父类AbstractApplicationContext的refresh()方法，

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refresh方法中调用了10个左右的方法，具体方法不一一细看，看今天分析的重点方法finishBeanFactoryInitialization方法，

@Overridepublic void refresh() throws BeansException, IllegalStateException {synchronized (this.startupShutdownMonitor) {// Prepare this context for refreshing.prepareRefresh(); // Tell the subclass to refresh the internal bean factory.ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context.prepareBeanFactory(beanFactory); try {// Allows post-processing of the bean factory in context subclasses.postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context.invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation.registerBeanPostProcessors(beanFactory); // Initialize message source for this context.initMessageSource(); // Initialize event multicaster for this context.initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses.onRefresh(); // Check for listener beans and register them.registerListeners(); // Instantiate all remaining (non-lazy-init) singletons.finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event.finishRefresh(); } 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(); // Reset 'active' flag.cancelRefresh(ex); // Propagate exception to caller.throw ex; } finally {// Reset common introspection caches in Spring's core, since we// might not ever need metadata for singleton beans anymore...resetCommonCaches(); }}}

在该方法中又调用了preInstantiateSingletons()方法，这个方法才是今天的主角，在该方法中会生成所有非懒加载的单例bean。方法定义如下

@Overridepublic void preInstantiateSingletons() throws BeansException {if (logger.isTraceEnabled()) {logger.trace("Pre-instantiating singletons in " + this); } // Iterate over a copy to allow for init methods which in turn register new bean definitions.// While this may not be part of the regular factory bootstrap, it does otherwise work fine.List beanNames = new ArrayList<>(this.beanDefinitionNames); // Trigger initialization of all non-lazy singleton beans...for (String beanName : beanNames) {RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName); if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {if (isFactoryBean(beanName)) {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)((SmartFactoryBean) factory)::isEagerInit,getAccessControlContext()); }else {isEagerInit = (factory instanceof SmartFactoryBean &&((SmartFactoryBean) factory).isEagerInit()); }if (isEagerInit) {getBean(beanName); }}}else {getBean(beanName); }}} // Trigger post-initialization callback for all applicable beans...for (String beanName : beanNames) {Object singletonInstance = getSingleton(beanName); if (singletonInstance instanceof SmartInitializingSingleton) {final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance; if (System.getSecurityManager() != null) {AccessController.doPrivileged((PrivilegedAction