浅谈Spring中几个PostProcessor的区别与联系浅谈Spring中几个PostProcessor的区

Spring几个PostProcessor的区别

首先明确 Bean 的生命周期：
查看 IOC 容器创建时的调用流程

spring-postProcessor的执行时机

BeanPostProcessor：
postProcessAfterInitialization调用时机：
InstantiationAwareBeanPostProcessor
总结：执行顺序

Spring几个PostProcessor的区别
首先明确 Bean 的生命周期：

首先注册 Bean 的定义信息；
然后创建 Bean 的实例；
最后初始化 Bean ，放入容器中。

按照执行的顺序，可以分为以下几个步骤：

BeanDefinitionRegistryPostProcessor 是在注册 Bean 定义信息前后调用;
BeanFactoryPostProcessor 是在创建 Bean 前后调用;
BeanPostProcessor 是在初始化 Bean 前后调用;

其中 BeanDefinitionRegistryPostProcessor 是 BeanFactoryPostProcessor 的子类，所以可以使用前者代替后者实现功能。

查看 IOC 容器创建时的调用流程
refresh 方法的代码如下：

// Allows post-processing of the bean factory in context subclasses.postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context.invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation.registerBeanPostProcessors(beanFactory); // Initialize message source for this context.initMessageSource(); // Initialize event multicaster for this context.initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses.onRefresh(); // Check for listener beans and register them.registerListeners(); // Instantiate all remaining (non-lazy-init) singletons.finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event.finishRefresh();

其中的 invokeBeanFactoryPostProcessors 就执行了注册定义信息和创建 Bean 的方法；而 finishBeanFactoryInitialization 执行了初始化 Bean 的方法。
具体的执行顺序大家可以自行打断点调试，由于涉及的源码过多，这里不再展示。

spring-postProcessor的执行时机 spring bean 的生命周期粗糙的分为以下步骤。

实例化（创建一个属性都为空的对象）---------》属性填充（populateBean，下文中这个步骤我都称为初始化）-----------》init方法的执行（invokerInitMethods，下文称为init）

postprocessor的方法就是穿插在这三个大的步骤中。

BeanPostProcessor：

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postProcessBeforeInitialization调用时机

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?
向上找调用者：

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继续向上：

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看以看出populateBean(初始化bean)-------------------》beanpostBeforeInitialization---------------------------------->invokeinitMethods(配置的init-method)

postProcessAfterInitialization调用时机：

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向上：

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可以看出在init-method方法之后

看以看出populateBean(初始化bean)-------------------》beanpostBeforeInitialization---------------------------------->invokeinitMethods(配置的init-method)------->postProcessAfterInitialization

public class MBeanPostProcessor implements BeanPostProcessor { @Override//populateBean之后invokeinitMethods之前public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {System.out.println("post bean before! ："+beanName); return bean; } @Override//invokeinitMethods之后public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {System.out.println("post bean after!"+beanName); return bean; }}

另一个重要的是：

InstantiationAwareBeanPostProcessor

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postProcessBeforeInstantiation调用时机：

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向上找调用者：

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继续向上：

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可以看出是在实例化之前：（也就是反射创建对象之前，如果postProcessBeforeInstantiation创建了一个非空的对象，则不会走实例化步骤。）
postProcessAfterInstantiation调用时机：

protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {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; }} // Give any InstantiationAwareBeanPostProcessors the opportunity to modify the// state of the bean before properties are set. This can be used, for example,// to support styles of field injection.boolean continueWithPropertyPopulation = true; if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {for (BeanPostProcessor bp : getBeanPostProcessors()) {if (bp instanceof InstantiationAwareBeanPostProcessor) {InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; //在这里执行if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {continueWithPropertyPopulation = false; break; }}}} if (!continueWithPropertyPopulation) {return; } 省略。。。。。 applyPropertyValues(beanName, mbd, bw, pvs); }

可以看出是在在初始化之前，具体是属性填充之前。（初始化之前，实例化之后）如果返回fales，则不会继续初始化，即不会属性填充。
postProcessPropertyValues调用时机：

protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {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; }} // Give any InstantiationAwareBeanPostProcessors the opportunity to modify the// state of the bean before properties are set. This can be used, for example,// to support styles of field injection.boolean continueWithPropertyPopulation = true; if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {for (BeanPostProcessor bp : getBeanPostProcessors()) {if (bp instanceof InstantiationAwareBeanPostProcessor) {InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {continueWithPropertyPopulation = false; break; }}}} 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) {for (BeanPostProcessor bp : getBeanPostProcessors()) {if (bp instanceof InstantiationAwareBeanPostProcessor) {InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName); if (pvs == null) {return; }}}}if (needsDepCheck) {checkDependencies(beanName, mbd, filteredPds, pvs); }} applyPropertyValues(beanName, mbd, bw, pvs); }

在postProcessAfterInstantiation之后，applyPropertyValues之前。（属性填充之前修改属性值）

总结：执行顺序