Spring5 源码阅读笔记（1.4.2.5）initializeBean(beanName, exposedObject, mbd)

先看一段代码，猜猜 Spring 启动后的打印顺序：

public class InitMethodBean implements InitializingBean{

    @PostConstruct
    public void postConstruct() {
        System.out.println("======构造方法之后=======");
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("======属性设置之后======");
    }

    public void initMethod() {
        System.out.println("======初始化方法======");
    }
}

结果：

合情合理的结果，但具体到源码层次的原因，在本小节中可以找到。

跟源码：
AbstractAutowireCapableBeanFactory

protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
	if (System.getSecurityManager() != null) {
		AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
			invokeAwareMethods(beanName, bean);
			return null;
		}, getAccessControlContext());
	}
	else {
		//调用Aware方法
		invokeAwareMethods(beanName, bean);
	}

	Object wrappedBean = bean;
	if (mbd == null || !mbd.isSynthetic()) {
		//重要程度 ：5 对类中某些特殊方法的调用，比如 @PostConstruct，Aware接口
		wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
	}

	try {
		//重要程度：5 InitializingBean接口，afterPropertiesSet，init-method属性调用
		invokeInitMethods(beanName, wrappedBean, mbd);
	}
	catch (Throwable ex) {
		throw new BeanCreationException(
				(mbd != null ? mbd.getResourceDescription() : null),
				beanName, "Invocation of init method failed", ex);
	}
	if (mbd == null || !mbd.isSynthetic()) {
		wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
	}

	return wrappedBean;
}

跟 invokeInitMethods：

protected void invokeInitMethods(String beanName, final Object bean, @Nullable RootBeanDefinition mbd)
		throws Throwable {
	//实现InitializingBean接口可以在类实例化后，做一些事情
	boolean isInitializingBean = (bean instanceof InitializingBean);
	if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
		if (logger.isTraceEnabled()) {
			logger.trace("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
		}
		if (System.getSecurityManager() != null) {
			try {
				AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> {
											//注意这个方法
					((InitializingBean) bean).afterPropertiesSet();
					return null;
				}, getAccessControlContext());
			}
			catch (PrivilegedActionException pae) {
				throw pae.getException();
			}
		}
		else {
			((InitializingBean) bean).afterPropertiesSet();
		}
	}

	if (mbd != null && bean.getClass() != NullBean.class) {
		String initMethodName = mbd.getInitMethodName();
		if (StringUtils.hasLength(initMethodName) &&
				!(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
				!mbd.isExternallyManagedInitMethod(initMethodName)) {
			//调用自定义初始化方法
			invokeCustomInitMethod(beanName, bean, mbd);
		}
	}
}