文章目录

• Pre
• Bean的生成过程
• org.springframework.beans.factory.config.BeanPostProcessor 介绍
• ApplicationContext注册Bean PostProcessor源码解析
• • AbstractApplicationContext#refresh
  • AbstractApplicationContext#registerBeanPostProcessors
  • PostProcessorRegistrationDelegate.registerBeanPostProcessors
• 回调BeanPostProcessors的时机源码解析
• 扩展示例
• 小结

Pre

Spring Boot - 扩展接口一览

Bean的生成过程

org.springframework.beans.factory.config.BeanPostProcessor 介绍

public interface BeanPostProcessor {@Nullabledefault Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {return bean;}@Nullabledefault Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {return bean;}}

如果BeanPostProcessors接囗的实现类被注册到ioc容器,那么该容器的每个Bean在调用初始化方法之前,都会获得该接口实现类的一个回调。

要使用BeanPostProcessord回调,就必须先在容器中注册实现该接口的类,那么如何注册呢?

• 若使用BeanFactory,则必须要显示的调用其addBeanPostProcessor方法进行注册,参数为BeanPostProcessor现类的实例;

• 使用ApplicationContext,那么容器会在配置文件在中自动寻找实现了 BeanPostProcessor口的Bean,然后自动注册,我们只需要配置个BeanPostProcessor现类的Bean可以了。

• 多个的BeanPostProcessorg实现类,只要实现Ordered接口,设置order属性就可以很轻确定不同实现类的处理顺序了;

• 接口中的两个方法都要将传入的bean回,不能返回null,如果返回的是nu么我们通过getBean将得不到目标

ApplicationContext注册Bean PostProcessor源码解析

AbstractApplicationContext#refresh

org.springframework.context.support.AbstractApplicationContext#refresh

来看下关键代码

public void refresh() throws BeansException, IllegalStateException {........// Register bean processors that intercept bean creation.registerBeanPostProcessors(beanFactory);........// Instantiate all remaining (non-lazy-init) singletons.// 实例化剩余的所有非延迟加载单例对象// 在上面的registerBeanPostProcessors中已经把所有BeanPostProcessors所有对象都已经实例化过了//  这加载的时候会判断bean是不是 FactoryBean类型的//  如果是FactoryBean类型，则getBean(&beanName),这里是把FactoryBean本身的对象给实例化了，而没有调它的getObject方法；// 还要判断是不是SmartFactoryBean类型的，SmartFactoryBean继承了FactoryBean接口；但是它多了一个	boolean isEagerInit();方法；这个方法就是判断是否需要通过FactoryBean的getObject()生成实例；// 如果不是FactoryBean类型，直接getBean就行了；// 还要判断是不是SmartInitializingSingleton接口，这个接口有个afterSingletonsInstantiated方法；// 循环所以bean判断是不是这个类型的，只要是这个类型就调用afterSingletonsInstantiated方法；finishBeanFactoryInitialization(beanFactory);........	 }

AbstractApplicationContext#registerBeanPostProcessors

先看 registerBeanPostProcessors

	/*** Instantiate and register all BeanPostProcessor beans,* respecting explicit order if given.* 
Must be called before any instantiation of application beans.*/protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);}

PostProcessorRegistrationDelegate.registerBeanPostProcessors

public static void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {/*** 代码走到了这里的时候其实 BeanDefinition数据已经被加载了，只是bean还没有被实例化所以这个是去容器里面找到所有类型为BeanPostProcessor的beanName*/String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));// 优先级最高的BeanPostProcessors，这类最先调用；需要实现PriorityOrdered接口List priorityOrderedPostProcessors = new ArrayList();//内部BeanPostProcessorsList internalPostProcessors = new ArrayList();//继承了Ordered接口，优先级比上面低一点List orderedPostProcessorNames = new ArrayList();//这就是普通的了，优先级最低List nonOrderedPostProcessorNames = new ArrayList();//下面的这些代码就是遍历所有postProcessorNames，按优先级排序；类型PriorityOrdered>Ordered>普通；在这个类型基础上，还要对他们的order属性就行排序；for (String ppName : postProcessorNames) {if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);priorityOrderedPostProcessors.add(pp);if (pp instanceof MergedBeanDefinitionPostProcessor) {internalPostProcessors.add(pp);}}else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {orderedPostProcessorNames.add(ppName);}else {nonOrderedPostProcessorNames.add(ppName);}}// First, register the BeanPostProcessors that implement PriorityOrdered.sortPostProcessors(beanFactory, priorityOrderedPostProcessors);registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);// Next, register the BeanPostProcessors that implement Ordered.List orderedPostProcessors = new ArrayList();for (String ppName : orderedPostProcessorNames) {BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);orderedPostProcessors.add(pp);if (pp instanceof MergedBeanDefinitionPostProcessor) {internalPostProcessors.add(pp);}}sortPostProcessors(beanFactory, orderedPostProcessors);registerBeanPostProcessors(beanFactory, orderedPostProcessors);// Now, register all regular BeanPostProcessors.List nonOrderedPostProcessors = new ArrayList();for (String ppName : nonOrderedPostProcessorNames) {//这里要注意一下了，看到没有，这个时候已经调用了getBean来生成实例对象了；BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);nonOrderedPostProcessors.add(pp);if (pp instanceof MergedBeanDefinitionPostProcessor) {internalPostProcessors.add(pp);}}registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);// 排序sortPostProcessors(beanFactory, internalPostProcessors);//注册registerBeanPostProcessors(beanFactory, internalPostProcessors);// 加入ApplicationListenerDetectorbeanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));}/*** 注册 BeanPostProcessor beans.* 容器中beanPostProcessors是一个ArrayList来持有这些BeanPostProcessors*/private static void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory, List postProcessors) {for (BeanPostProcessor postProcessor : postProcessors) {beanFactory.addBeanPostProcessor(postProcessor);}}
@Overridepublic void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");this.beanPostProcessors.remove(beanPostProcessor);this.beanPostProcessors.add(beanPostProcessor);//将是否 hasInstantiationAwareBeanPostProcessors设置为true if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {this.hasInstantiationAwareBeanPostProcessors = true;}if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {this.hasDestructionAwareBeanPostProcessors = true;}}

回调BeanPostProcessors的时机源码解析

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

doGetBean 重点看

// Create bean instance.
if (mbd.isSingleton()) {sharedInstance = getSingleton(beanName, () -> {try {return createBean(beanName, mbd, args);}catch (BeansException ex) {// Explicitly remove instance from singleton cache: It might have been put there// eagerly by the creation process, to allow for circular reference resolution.// Also remove any beans that received a temporary reference to the bean.destroySingleton(beanName);throw ex;}});beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}

继续看 createBean

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

doCreateBean重点看

// Initialize the bean instance.
Object exposedObject = bean;
try {// 属性设置populateBean(beanName, mbd, instanceWrapper);// BeanPostProcessors两个方法都在这里面exposedObject = initializeBean(beanName, exposedObject, mbd);
}

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

继续核心 initializeBean

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {if (System.getSecurityManager() != null) {AccessController.doPrivileged((PrivilegedAction