Spring - InstantiationAwareBeanPostProcessor 扩展接口

Posted 2022-12-13 小小工匠

文章目录

• Pre
• org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor
• InstantiationAwareBeanPostProcessor 注册过程源码分析
• • postProcessBeforeInstantiation的执行时机源码解析
• 使用场景 ： 创建代理类

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Pre

Spring Boot - 扩展接口一览

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org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor

注意下： Initialization 表示 实例化 （意思是对象还未生成） 。 Instantiation 表示 初始化 （意思是对象已经生成） 。

接口继承了BeanPostProcess接口 , 从方法上我们也可以看出 InstantiationAwareBeanPostProcessor 做了一些扩展 。

BeanPostProcess接口只在bean的初始化阶段进行扩展（注入spring上下文前后），而InstantiationAwareBeanPostProcessor接口在此基础上增加了3个方法，使得扩展接口可以在实例化阶段和属性注入阶段

该类主要的扩展点有以下5个方法，主要在bean生命周期的两大阶段：实例化阶段 和初始化阶段 ，

(1)实例化: 实例化的过程是一个创建Bean的过程,即调用Bean构造函数,单例的Bean入单例池中

(2)初始化: 初始化的过程是一个赋值的过程,即调用Bean的setter方法,设置Bean属性

InstantiationAwareBeanPostProcessor作用于过程(1)实例化前后; BeanPostProcessor用于过程(2)初始化前后

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按调用顺序，我们来看一下

• postProcessBeforeInstantiation：实例化bean之前，相当于new这个bean之前
• postProcessAfterInstantiation：实例化bean之后，相当于new这个bean之后
• postProcessPropertyValues： bean已经实例化完成，在属性注入时阶段触发， @Autowired,@Resource等注解原理基于此方法实现
• postProcessBeforeInitialization：初始化bean之前，相当于把bean注入spring上下文之前
• postProcessAfterInitialization：初始化bean之后，相当于把bean注入spring上下文之后

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InstantiationAwareBeanPostProcessor 注册过程源码分析

我们还是从

org.springframework.context.support.AbstractApplicationContext#refresh

开始看 ，主要是下面两个方法

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

.......

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

看下调用栈

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

createBean跟进去

@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;

	

通过上面的代码，我们可以看到在执行doCreateBean之前有resolveBeforelnstantiation方法; 看注释

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

• resolveBeforelnstantiation判断执行InstantiationAwareBeanPostProcessor.postProcessBeforelInstantiationg接口方法实现;
• doCreateBean创建bean方法;

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postProcessBeforeInstantiation的执行时机源码解析

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

重点看 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;
	

继续 applyBeanPostProcessorsBeforeInstantiation

	/**
	 * Apply InstantiationAwareBeanPostProcessors to the specified bean definition
	 * (by class and name), invoking their @code postProcessBeforeInstantiation methods.
	 * <p>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;
	

当然了也有 postProcessAfterInitialization

	@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;
	

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使用场景 ： 创建代理类

 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;
    

    
    

我们可以看到 InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation 生成了代理类后，直接执行了 初始化后的动作 BeanPostProcessor#postProcessAfterInitialization 。