Spring IoC源码解析之getBean

一、实例化所有的非懒加载的单实例Bean

　　从org.springframework.context.support.AbstractApplicationContext#refresh方法开发，进入到实例化所有的非懒加载的单实例Bean的finishBeanFactoryInitialization(beanFactory)的方法：

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
        // 为Bean工厂设置类型转化器
        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));
        }

        // 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(new StringValueResolver() {
                @Override
                public String resolveStringValue(String strVal) {
                    return getEnvironment().resolvePlaceholders(strVal);
                }
            });
        }

        // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
        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);

        //冻结所有的Bean定义 ， 至此注册的Bean定义将不被修改或任何进一步的处理
        beanFactory.freezeConfiguration();

        //实例化剩下的单实例Bean
        beanFactory.preInstantiateSingletons();
    }

　　进入实例化剩下的单实例Bean的beanFactory.preInstantiateSingletons()的方法：

public void preInstantiateSingletons() throws BeansException {
        if (logger.isDebugEnabled()) {
            logger.debug("Pre-instantiating singletons in " + this);
        }

        //获取我们容器中所有Bean定义的名称
        List beanNames = new ArrayList<>(this.beanDefinitionNames);

        //循环我们所有的bean定义名称
        for (String beanName : beanNames) {
            //合并我们的bean定义
            RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
            //根据bean定义判断是不是抽象的 && 不是单例的 && 不是懒加载的
            if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
                //是否FactoryBean
                if (isFactoryBean(beanName)) {
                    //是 给beanName+前缀 & 符号
                    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());
                        }
                        //调用真正的getBean
                        if (isEagerInit) {
                            getBean(beanName);
                        }
                    }
                }
                else {//非工厂Bean就是普通的bean
                    getBean(beanName);
                }
            }
        }

        //获取所有的bean的名称 至此所有的单实例的bean已经加入到单实例Bean的缓存池中，所谓的单实例缓存池实际上就是一个ConcurrentHashMap
        for (String beanName : beanNames) {
            //从单例缓存池中获取所有的对象
            Object singletonInstance = getSingleton(beanName);
            //判断当前的bean是否实现了SmartInitializingSingleton接口
            if (singletonInstance instanceof SmartInitializingSingleton) {
                final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
                if (System.getSecurityManager() != null) {
                    AccessController.doPrivileged((PrivilegedAction