Spring FactoryBean实例化过程源码分析

Spring在执行refresh方法时，会将所有单例和未配置延迟初始化的beanDefinition进行实例化。

	@Override
	public 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();

				// 实例化所有的单例bean
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				finishRefresh();
			}

			catch (BeansException ex) {
	
			}

			finally {
				// Reset common introspection caches in Spring's core, since we
				// might not ever need metadata for singleton beans anymore...
				resetCommonCaches();
			}
		}
	}

执行finishBeanFactoryInitialization()方法时，最终执行beanFactory.finishBeanFactoryInitialization()方法

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
		// Initialize conversion service for this context.
		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(strVal -> 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);

		// Allow for caching all bean definition metadata, not expecting further changes.
		beanFactory.freezeConfiguration();

		// 实例化所有的单例bean
		beanFactory.preInstantiateSingletons();
	}

preInstantiateSingletons方法：

该方法位于DefaultListableBeanFactory中

	@Override
	public void preInstantiateSingletons() throws BeansException {
		if (logger.isTraceEnabled()) {
			logger.trace("Pre-instantiating singletons in " + this);
		}

		//容器中的所有bean
		List beanNames = new ArrayList<>(this.beanDefinitionNames);

		// 遍历进行bean实例化
		for (String beanName : beanNames) {
            //获取bean对应的beanDefinition
			RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
            //beanDefinition满足非抽象、单例、非延迟初始化才进行bean实例化
			if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
                //判断是否为FactoryBean
				if (isFactoryBean(beanName)) {
                    //FactoryBean对象的beanName需增加&符号用于与普通bean进行区分
					Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
                    //FactoryBean实例化成功
					if (bean instanceof FactoryBean) {
						FactoryBean factory = (FactoryBean) bean;
                        //是否提前初始化FactoryBean实际的bean
						boolean isEagerInit;
                        //factoryBean实现了SmartFactoryBean接口时，会根据接口方法isEagerInit进行是否提前初始化
						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) {
                            //FactoryBean配置了提前初始化时，还需进行实际bean初始化
							getBean(beanName);
						}
					}
				}
				else {
                    //普通bean实例化
					getBean(beanName);
				}
			}
		}

		// 调用容器中所有的SmartInitializingSingleton实例，容器已完成bean实例化
		for (String beanName : beanNames) {
			Object singletonInstance = getSingleton(beanName);
			if (singletonInstance instanceof SmartInitializingSingleton) {
				SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
				if (System.getSecurityManager() != null) {
					AccessController.doPrivileged((PrivilegedAction