InstantiationAwareBeanPostProcessor源码解析

/**
* org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.resolveBeforeInstantiation 
* 作用：在实例化之前解析是否有快捷创建的Bean，既是通过postProcessBeforeInstantiation返回的Bean
* 内部调用两个重要的方法：
*   1、applyBeanPostProcessorsBeforeInstantiation：内部遍历调用postProcessBeforeInstantiation方法【在实例化之前调用】
*   2、applyBeanPostProcessorsAfterInitialization：如果postProcessBeforeInstantiation方法返回了快捷的Bean，内部遍历调用postProcessBeforeInstantiation方法【在初始化之后调用】
*/
protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
		Object bean = null;
		if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
			// Make sure bean class is actually resolved at this point.
			if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
				Class<?> targetType = determineTargetType(beanName, mbd);
				if (targetType != null) {
				    //调用方法，内部遍历调用postProcessBeforeInstantiation方法【在实例化之前调用】
					bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
					//如果返回了快捷的Bean
					if (bean != null) {
					    //如果postProcessBeforeInstantiation方法返回了快捷的Bean，内部遍历调用postProcessBeforeInstantiation方法【在初始化之后调用】
						bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
					}
				}
			}
			mbd.beforeInstantiationResolved = (bean != null);
		}
		return bean;
	}
	
	/**
	*   org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInstantiation
	*   作用：调用postProcessBeforeInstantiation方法
    */
	protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName)
    			throws BeansException {
	        //遍历所有的后置处理器
    		for (BeanPostProcessor bp : getBeanPostProcessors()) {
    		    //判断是否是InstantiationAwareBeanPostProcessor类型的，如果是的，调用postProcessBeforeInstantiation方法获取快捷Bean
    			if (bp instanceof InstantiationAwareBeanPostProcessor) {
    				InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
    				Object result = ibp.postProcessBeforeInstantiation(beanClass, beanName);
    				if (result != null) {
    					return result;
    				}
    			}
    		}
    		return null;
    	}
	
	/**
	*   org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsAfterInitialization
	*   作用：遍历调用postProcessAfterInitialization
	*/
	public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
    			throws BeansException {
    		Object result = existingBean;
    		for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
    			result = beanProcessor.postProcessAfterInitialization(result, beanName);
    			if (result == null) {
    				return result;
    			}
    		}
    		return result;
    	}

/**
* org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean
* 填充指定Bean的属性
* 在该方法内部遍历所有的BeanPostPorcessor，调用postProcessAfterInstantiation方法
*/
protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
        //获取属性
		PropertyValues pvs = mbd.getPropertyValues();
		if (bw == null) {
			if (!pvs.isEmpty()) {
				throw new BeanCreationException(
						mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
			}
			else {
				// Skip property population phase for null instance.
				return;
			}
		}
        //**********************逻辑开始执行********************
        //标志，判断是否继续执行属性填充，默认为false
		boolean continueWithPropertyPopulation = true;
        //判断ioc容器中是否存在InstantiationAwareBeanPostProcessors(
		if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
		    //遍历所有的BeanPostProcessor
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
			    //判断类型是InstantiationAwareBeanPostProcessor
				if (bp instanceof InstantiationAwareBeanPostProcessor) {
					InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
					//执行postProcessAfterInstantiation方法
					if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
					    //返回结果为false，那么赋值continueWithPropertyPopulation=false，表示不继续执行属性填充
						continueWithPropertyPopulation = false;
						break;
					}
				}
			}
		}
        //如果continueWithPropertyPopulation为false，直接返回，不执行下面的步骤
		if (!continueWithPropertyPopulation) {
			return;
		}
        //
		if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
				mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
			MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
			// Add property values based on autowire by name if applicable.
			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
				autowireByName(beanName, mbd, bw, newPvs);
			}
			// Add property values based on autowire by type if applicable.
			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
				autowireByType(beanName, mbd, bw, newPvs);
			}
			pvs = newPvs;
		}
		boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
		boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);
		if (hasInstAwareBpps || needsDepCheck) {
			PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
			if (hasInstAwareBpps) {
			    //同样是遍历BeanPostProcessor
				for (BeanPostProcessor bp : getBeanPostProcessors()) {
					if (bp instanceof InstantiationAwareBeanPostProcessor) {
						InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
						//执行postProcessPropertyValues方法
						pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
						if (pvs == null) {
							return;
						}
					}
				}
			}
			if (needsDepCheck) {
				checkDependencies(beanName, mbd, filteredPds, pvs);
			}
		}
		//重要的一步，设置属性
		applyPropertyValues(beanName, mbd, bw, pvs);
	}

/**
* org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean的代码片段
*/
if (hasInstAwareBpps || needsDepCheck) {
			PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
			if (hasInstAwareBpps) {
			    //遍历调用postProcessPropertyValues方法
				for (BeanPostProcessor bp : getBeanPostProcessors()) {
					if (bp instanceof InstantiationAwareBeanPostProcessor) {
						InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
						pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
						//如果返回的pvs是null，直接返回
						if (pvs == null) {
							return;
						}
					}
				}
			}
			if (needsDepCheck) {
				checkDependencies(beanName, mbd, filteredPds, pvs);
			}
		}   
        //执行真正的属性填充
		applyPropertyValues(beanName, mbd, bw, pvs);

@Component
public class MyInstantiationAwareBeanPostProcessor implements InstantiationAwareBeanPostProcessor {
    /**
     * 在实例化之前调用，如果返回null，一切按照正常顺序执行，如果返回的是一个实例的对象，那么这个将会跳过实例化、初始化的过程
     * @param beanClass
     * @param beanName
     * @return
     */
    @Override
    public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
        if (beanClass == User.class) {
            System.out.println("postProcessBeforeInstantiation执行");
            return null;
        }
        return null;
    }
    /**
     * 在实例化之后，postProcessBeforeInitialization之前执行
     * @param bean
     * @param beanName
     * @return
     * @throws BeansException
     */
    @Override
    public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
        if (bean instanceof User) {
            System.out.println("postProcessAfterInstantiation执行");
            return true;
        }
        return true;
    }
    /**
     * 实例化之后调用，属性填充之前
     * @param pvs PropertyValues对象，用于封装指定类的对象，简单来说就是PropertyValue的集合，里面相当于以key-value形式存放类的属性和值
     * @param pds PropertyDescriptor对象数组，PropertyDescriptor相当于存储类的属性，不过可以调用set，get方法设置和获取对应属性的值
     * @param bean 当前的bean
     * @param beanName beanName
     * @return 如果返回null，那么将不会进行后续的属性填充，比如依赖注入等，如果返回的pvs额外的添加了属性，那么后续会填充到该类对应的属性中。
     */
    @Override
    public PropertyValues postProcessPropertyValues(PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {
        if (pvs instanceof MutablePropertyValues&&bean instanceof User){
           MutablePropertyValues mutablePropertyValues= (MutablePropertyValues) pvs;
           HashMap<Object, Object> map = new HashMap<>();
           map.put("name","陈加兵");
           map.put("age",44);
           mutablePropertyValues.addPropertyValues(map);
           return mutablePropertyValues;
        }
        /**使用pds设置值
        if (bean instanceof User) {
            for (PropertyDescriptor descriptor:pds) {
                try {
                    if ("name".equals(descriptor.getName())) {
                        descriptor.getWriteMethod().invoke(bean, "陈加兵");
                    }else if("age".equals(descriptor.getName())){
                        descriptor.getWriteMethod().invoke(bean,40);
                    }
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
            return null;
        }**/
        return pvs;
    }
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if (bean instanceof User) {
            System.out.println("postProcessBeforeInitialization执行");
        }
        return bean;
    }
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if (bean instanceof User) {
            System.out.println("postProcessAfterInitialization执行");
        }
        return bean;
    }
}