Spring - InstantiationAwareBeanPostProcessor 扩展接口

org.springframework.context.support.AbstractApplicationContext#refresh

.......
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);

.......

// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);

org.springframework.context.support.PostProcessorRegistrationDelegate#registerBeanPostProcessors()
	BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
		org.springframework.beans.factory.support.AbstractBeanFactory#getBean
		  org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean	
			  org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#createBean

@Override
	protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
	// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
			Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
			if (bean != null) {
				return bean;
			}
	//省略....
	Object beanInstance = doCreateBean(beanName, mbdToUse, args);
	return beanInstance;

	}

// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.

org.springframework.context.support.PostProcessorRegistrationDelegate#registerBeanPostProcessors()
	BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
		org.springframework.beans.factory.support.AbstractBeanFactory#getBean
		  org.springframework.beans.factory.support.AbstractBeanFactory#doGetBean	
			  org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#createBean
					org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#resolveBeforeInstantiation

	/**
	 * Apply before-instantiation post-processors, resolving whether there is a
	 * before-instantiation shortcut for the specified bean.
	 * @param beanName the name of the bean
	 * @param mbd the bean definition for the bean
	 * @return the shortcut-determined bean instance, or {@code null} if none
	 */
	@Nullable
	protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
		Object bean = null;
		//如果beforeInstantiationResolved还没有设置或者是false（说明还没有需要在实例化前执行的操作）
		if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
			// Make sure bean class is actually resolved at this point.
			// 判断是否有注册过InstantiationAwareBeanPostProcessor类型的bean
			if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
				Class<?> targetType = determineTargetType(beanName, mbd);
				if (targetType != null) {
					//执行
					bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
					if (bean != null) {
						bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
					}
				}
			}
			mbd.beforeInstantiationResolved = (bean != null);
		}
		return bean;
	}

	/**
	 * Apply InstantiationAwareBeanPostProcessors to the specified bean definition
	 * (by class and name), invoking their {@code postProcessBeforeInstantiation} methods.
	 * Any returned object will be used as the bean instead of actually instantiating
	 * the target bean. A {@code null} return value from the post-processor will
	 * result in the target bean being instantiated.
	 * @param beanClass the class of the bean to be instantiated
	 * @param beanName the name of the bean
	 * @return the bean object to use instead of a default instance of the target bean, or {@code null}
	 * @see InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation
	 */
	@Nullable
	protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
		// 循环处理
		for (InstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().instantiationAware) {
			Object result = bp.postProcessBeforeInstantiation(beanClass, beanName);
			//只要有一个result不为null；后面的所有 后置处理器的方法就不执行了，直接返回(所以执行顺序很重要)
			if (result != null) {
				return result;
			}
		}
		return null;
	}

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

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

 package com.artisan.bootspringextend.testextends;

import com.artisan.bootspringextend.service.ArtisanServiceImpl;
import com.artisan.bootspringextend.service.ClassA;
import com.artisan.bootspringextend.service.ClassAInterceptor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.BeansException;
import org.springframework.beans.PropertyValues;
import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
import org.springframework.cglib.proxy.Enhancer;
import org.springframework.context.annotation.Configuration;

/**
 * @author 小工匠
 * @version 1.0
 * @description:
 * @date 2022/11/28 0:33
 * @mark: show me the code , change the world
 */

@Slf4j
@Configuration
public class ExtendInstantiationAwareBeanPostProcessor implements InstantiationAwareBeanPostProcessor {

    private static final String VALUE = "classA";
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {

        if (VALUE.equals(beanName)) {
            log.info("4  beanName {}-----> postProcessBeforeInitialization", beanName);

        }
        return bean;
    }


    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if (VALUE.equals(beanName)) {
            log.info("5   beanName {}-----> postProcessAfterInitialization", beanName);

        }

        return bean;
    }

    @Override
    public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {


        if (beanClass == ClassA.class) {
            log.info("1  beanName {} -----> postProcessBeforeInstantiation", beanName);

            Enhancer enhancer = new Enhancer();
            enhancer.setSuperclass(beanClass);
            enhancer.setCallback(new ClassAInterceptor());

            ClassA classA = (ClassA) enhancer.create();
            log.info("proxy created ---->{}", classA.toString());

            return classA;
        }

        return null;
    }


    @Override
    public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {

        if (VALUE.equals(beanName)) {
            log.info("2   beanName {}-----> postProcessAfterInstantiation", beanName);

        }

        return false;
    }


    @Override
    public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) throws BeansException {

        if (VALUE.equals(beanName)) {
            log.info("3   beanName {} -----> postProcessProperties", beanName);

        }
        return pvs;
    }
}