今天复习一下Spring IOC源码发现org.springframework.beans.factory.support.DefaultListableBeanFactory#preInstantiateSingletons()方法里除了getBean()方法执行逻辑外，还有以下代码块：

for (String beanName : beanNames) {
			Object singletonInstance = getSingleton(beanName);
			// 如果bean实现了SmartInitializingSingleton
			if (singletonInstance instanceof SmartInitializingSingleton) {
				final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
				// 执行afterSingletonsInstantiated()方法
				if (System.getSecurityManager() != null) {
					AccessController.doPrivileged(new PrivilegedAction<Object>() {
						@Override
						public Object run() {
					smartSingleton.afterSingletonsInstantiated();
							return null;
						}
					}, getAccessControlContext());
				}
				else {
					smartSingleton.afterSingletonsInstantiated();
				}
			}
		}

从代码中我们可以推断出，如果bean实现了SmartInitializingSingleton接口，则会在所有bean都初始化成功后执行afterSingletonsInstantiated()方法。