Spring解析之finishBeanFactoryInitialization即初始化单例bean
七千字长文深刻解读,Spirng中是如何初始化单例bean的,和面试中最常问的Spring是如何解决循环依赖?
今天解读Spring核心方法refresh()中最最重要的一个方法finishBeanFactoryInitialization()方法,该方法负责初始化所有的单例bean。
finishBeanFactoryInitialization()方法位于refresh()中下标为8的位置。
到目前为止,应该说是是 BeanFactory 已经创建完成,并且所有的实现了 BeanFactoryPostProcessor 接口的 Bean 都已经初始化并且其中的 postProcessBeanFactory(factory) 方法已经得到回调执行了。而且 Spring 已经"手动"注册了一些特殊的 Bean,如 environment 、systemProperties 等。
剩下的就是初始化 singleton beans 了,大多数我们的业务中都是单例bean,就像我们写的@Controller、@Service的类(没有设置懒加载的)都是在这个地方初始化,以供我们使用,如果没有设置懒加载,那么 Spring 会在接下来初始化所有的 singleton beans。
我们先看一下refresh()的源码,大概看下finishBeanFactoryInitialization(beanFactory)所处的位置。 @Override public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. //1、刷新前的准备 prepareRefresh(); // Tell the subclass to refresh the internal bean factory. //2、将会初始化 BeanFactory、加载 Bean、注册 Bean ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. //3、设置 BeanFactory 的类加载器,添加几个 BeanPostProcessor,手动注册几个特殊的 bean prepareBeanFactory(beanFactory); try { //4、模板方法 // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. //执行BeanFactory后置处理器 invokeBeanFactoryPostProcessors(beanFactory); // 5、Register bean processors that intercept bean creation. //注册bean后置处理器 registerBeanPostProcessors(beanFactory); // Initialize message source for this context. //国际化 initMessageSource(); // Initialize event multicaster for this context. initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses. //6、模板方法--springboot实现了这个方法 onRefresh(); // Check for listener beans and register them. //7、注册监听器 registerListeners(); // Instantiate all remaining (non-lazy-init) singletons. //8、完成bean工厂的初始化**方法重要********************************************** finishBeanFactoryInitialization(beanFactory); //9、 Last step: publish corresponding event. finishRefresh(); } 1.2.3.4.5.6.7.8.9.10.11.12.13.14.15.16.17.18.19.20.21.22.23.24.25.26.27.28.29.30.31.32.33.34.35.36.37.38.39.40.41.42.43.44.45.46.47.48.49.50.
我们深入finishBeanFactoryInitialization(beanFactory)中,里面的调用线路错综复杂,还望读者可以做好心理准备。 /** * 负责单例bean的初始化 * Finish the initialization of this context"s bean factory, * initializing all remaining singleton beans. */ protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) { // Initialize conversion service for this context. //最先初始化名字为 conversionService的类,conversionService类 它用来将前端传过来的参数和后端的 controller 方法上的参数进行绑定的时候用 //尤其是用于非基础类型的转换 if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) && beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) { beanFactory.setConversionService( //初始化在getBean()方法中实现 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(strVal -> getEnvironment().resolvePlaceholders(strVal)); } // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early. // 先初始化 LoadTimeWeaverAware 类型的 Bean aop相关注:大概有个印象,以后解析aop会和它串起来。 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. //freeze的单词意思是冻结,这个时候已经开始预初始化, bean 定义解析、加载、注册先停止 beanFactory.freezeConfiguration(); // Instantiate all remaining (non-lazy-init) singletons. //开始初始化 beanFactory.preInstantiateSingletons(); } 1.2.3.4.5.6.7.8.9.10.11.12.13.14.15.16.17.18.19.20.21.22.23.24.25.26.27.28.29.30.31.32.33.34.35.36.37.38.39.40.41.
该方法是判断bean的一系列是不是属于某个类型的bean,如果是就调用getBean()方法,如果不是,就调用beanFactory.preInstantiateSingletons()进行初始化,我们先把getBean()放一放,重点看一看beanFactory.preInstantiateSingletons()方法。 @Override public 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. // this.beanDefinitionNames 保存了所有的 beanNames List beanNames = new ArrayList<>(this.beanDefinitionNames); // Trigger initialization of all non-lazy singleton beans... //// 下面这个循环,触发所有的非懒加载的 singleton beans 的初始化操作 for (String beanName : beanNames) { RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName); // 非抽象、非懒加载的 singletons。如果配置了 "abstract = true",那是不需要初始化的 if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) { // 处理 FactoryBean (负责初始化工厂的bean) if (isFactoryBean(beanName)) { // FactoryBean 的话,在 beanName 前面加上 ‘&’ 符号 //此处调用getBean()方法 Object bean = getBean(FACTORY_BEAN_PREFIX + beanName); if (bean instanceof FactoryBean) { FactoryBean<?> factory = (FactoryBean<?>) bean; // 判断当前 FactoryBean 是否是 SmartFactoryBean 的实现 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 { // 对于普通的 Bean,只要调用 getBean(beanName) 这个方法就可以进行初始化了 getBean(beanName); } } } // Trigger post-initialization callback for all applicable beans... // 到这里说明所有的非懒加载的 singleton beans 已经完成了初始化 // 如果我们定义的 bean 是实现了 SmartInitializingSingleton 接口的,那么在这里得到回调 //如果你想在单例bean初始化后做一些事 那就实现该接口 for (String beanName : beanNames) { Object singletonInstance = getSingleton(beanName); if (singletonInstance instanceof SmartInitializingSingleton) { SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance; if (System.getSecurityManager() != null) { AccessController.doPrivileged((PrivilegedAction