BeanPostProcessor principle of learning

"Spring-source analysis" notes

1, custom BeanPostProcessor

@Component
public class MyBeanPostProcessor implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        // TODO Auto-generated method stub
        System.out.println("postProcessBeforeInitialization..."+beanName+"=>"+bean);
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        // TODO Auto-generated method stub
        System.out.println("postProcessAfterInitialization..."+beanName+"=>"+bean);
        return bean;
    }
}

2, wherein the function call chain postProcessBeforeInitialization follows:

   When the vessel started: refresh () -> finishBeanFactoryInitialization (beanFactory) -> beanFactory.preInstantiateSingletons () -> this.getBean (beanName) ->

                                  this.doGetBean(name, (Class)null, (Object[])null, false)--this.getSingleton(beanName, new ObjectFactory<Object>()-->

                                  singletonFactory.getObject()-->AbstractBeanFactory.this.createBean(beanName, mbd, args)-->this.doCreateBean(beanName, mbdToUse, args)

                                 -->this.initializeBean(beanName, exposedObject, mbd) 

                             

     Before performing the initializeBean (), it is executed first populateBean () function, which is mainly assigned to the various attributes of Bean.

　　　　　this.populateBean(beanName, mbd, instanceWrapper);
        if (exposedObject != null) {
             exposedObject = this.initializeBean(beanName, exposedObject, mbd);
        }

3, in initializeBean (beanName, exposedObject, mbd) observed calling code

　　　　if (mbd == null || !mbd.isSynthetic()) {
            wrappedBean = this.applyBeanPostProcessorsBeforeInitialization(bean, beanName);
        }
　　　　//初始化方法执行代码
        try {
            this.invokeInitMethods(beanName, wrappedBean, mbd);
        } catch (Throwable var6) {
            throw new BeanCreationException(mbd != null ? mbd.getResourceDescription() : null, beanName, "Invocation of init method failed", var6);
        }

        if (mbd == null || !mbd.isSynthetic()) {
            wrappedBean = this.applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        }

4. Check the function code applyBeanPostProcessorsBeforeInitialization and applyBeanPostProcessorsAfterInitialization

    Traversing all the BeanPostProcessor obtained container; executed one by one beforeInitialization, but returned a null, out of for loop, the latter does not execute BeanPostProcessor.postProcessorsBeforeInitialization

   For each container Bean instance, step 3 if they meet the conditions of the statement, will perform these two functions, the interface will enter BeanPostProcessor not realize these two functions.

@Override
    public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
            throws BeansException {

        Object result = existingBean;
        for (BeanPostProcessor processor : getBeanPostProcessors()) {
            result = processor.postProcessBeforeInitialization(result, beanName);
            if (result == null) {
                return result;
            }
        }
        return result;
    }

    @Override
    public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
            throws BeansException {

        Object result = existingBean;
        for (BeanPostProcessor processor : getBeanPostProcessors()) {
            result = processor.postProcessAfterInitialization(result, beanName);
            if (result == null) {
                return result;
            }
        }
        return result;
    }