【Spring注解系列11】Spring后置处理器BeanPostProcessor用法与原理

1.BeanPostProcessor原理

先说，bean的后置处理器BeanPostProcessor接口中两个方法：

• postProcessBeforeInitialization:在初始化之前工作
• postProcessAfterInitialization:在初始化之后工作

 

BeanPostProcessor原理

• populateBean(beanName, mbd, instanceWrapper);//给bean进行属性赋值
• 调用initializeBean方法，执行后置处理器和指定的初始化方法。（详细过程见下面源码）
• 后置处理器BeanPostProcessor执行过程是，遍历得到容器中所有的BeanPostProcessor；挨个执行beforeInitialization，一但返回null，跳出for循环，不会执行后面的BeanPostProcessor.postProcessorsBeforeInitialization

 

核心执行方法initializeBean：

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#initializeBean

initializeBean

{

applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);

invokeInitMethods(beanName, wrappedBean, mbd);执行自定义初始化

applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);

}

/**
	 * Initialize the given bean instance, applying factory callbacks
	 * as well as init methods and bean post processors.
	 * 
Called from {@link #createBean} for traditionally defined beans,
	 * and from {@link #initializeBean} for existing bean instances.
	 * @param beanName the bean name in the factory (for debugging purposes)
	 * @param bean the new bean instance we may need to initialize
	 * @param mbd the bean definition that the bean was created with
	 * (can also be {@code null}, if given an existing bean instance)
	 * @return the initialized bean instance (potentially wrapped)
	 * @see BeanNameAware
	 * @see BeanClassLoaderAware
	 * @see BeanFactoryAware
	 * @see #applyBeanPostProcessorsBeforeInitialization
	 * @see #invokeInitMethods
	 * @see #applyBeanPostProcessorsAfterInitialization
	 */
	protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
		if (System.getSecurityManager() != null) {
			AccessController.doPrivileged((PrivilegedAction