spring源码拓展点3之addBeanPostProcesser

概述

在refresh方法中的prepareBeanFactory方法中，有一个拓展点：addBeanPostProcessor。即通过注入Aware对象从而将容器中的某些值设置到某个bean中。

beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

aware接口调用

invokeAwareMethods

该方法在doCreateBean的initializeBean方法中。
只是BeanNameAware BeanClassLoaderAware BeanFactoryAware时，是通过invokeAwareMethods方法调用的。

	private void invokeAwareMethods(String beanName, Object bean) {if (bean instanceof Aware) {if (bean instanceof BeanNameAware) {((BeanNameAware) bean).setBeanName(beanName);}if (bean instanceof BeanClassLoaderAware) {ClassLoader bcl = getBeanClassLoader();if (bcl != null) {((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);}}if (bean instanceof BeanFactoryAware) {((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);}}}

若是其他aware接口则是通过实现BeanPostProcessor调用的，如ApplicationContextAwareProcessor

ApplicationContextAwareProcessor

class ApplicationContextAwareProcessor implements BeanPostProcessor 

重写了postProcessBeforeInitialization方法，在这里是具体的处理逻辑，调用逻辑是在invokeAwareMethods的applyBeanPostProcessorsBeforeInitialization方法中

	@Override@Nullablepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)){return bean;}AccessControlContext acc = null;if (System.getSecurityManager() != null) {acc = this.applicationContext.getBeanFactory().getAccessControlContext();}if (acc != null) {AccessController.doPrivileged((PrivilegedAction<Object>) () -> {invokeAwareInterfaces(bean);return null;}, acc);}else {invokeAwareInterfaces(bean);}return bean;}

调用aware接口

private void invokeAwareInterfaces(Object bean) {if (bean instanceof EnvironmentAware) {((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());}if (bean instanceof EmbeddedValueResolverAware) {((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);}if (bean instanceof ResourceLoaderAware) {((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);}if (bean instanceof ApplicationEventPublisherAware) {((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);}if (bean instanceof MessageSourceAware) {((MessageSourceAware) bean).setMessageSource(this.applicationContext);}if (bean instanceof ApplicationContextAware) {((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);}}

applyBeanPostProcessorsBeforeInitialization

该方法也在initializeBean中

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {if (System.getSecurityManager() != null) {AccessController.doPrivileged((PrivilegedAction<Object>) () -> {invokeAwareMethods(beanName, bean);return null;}, getAccessControlContext());}else {// 对实现了aware接口的bean执行aware实现方法invokeAwareMethods(beanName, bean);}Object wrappedBean = bean;if (mbd == null || !mbd.isSynthetic()) {// 调用BeanPostProcessor的postProcessBeforeInitialization方法的实现wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);}....

getBeanPostProcessors方法获取所有的BeanPostProcessors，然后遍历调用postProcessBeforeInitialization方法

	@Overridepublic Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)throws BeansException {Object result = existingBean;for (BeanPostProcessor processor : getBeanPostProcessors()) {Object current = processor.postProcessBeforeInitialization(result, beanName);if (current == null) {return result;}result = current;}return result;}

我们可以在该方法的实现中找到自定义的BeanPostProcessor从而实现拓展

其他

拓展点： parseCustomElement