Spring週期之BeanPostProcessor的應用

 

Spring底層本身也在許多地方用到了BeanPostProcessor機制，在組件創建完並且屬性賦值完成，並且在執行初始化的前後對Bean的一些封裝等，BeanPostProcessor的繼承關係圖如下：

 

1. ApplicationContextAwareProcessor： 爲組件注入IOC容器：

@Override
public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {
	AccessControlContext acc = null;
		if (System.getSecurityManager() != null &&
			(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
					bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
					bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) {
		acc = this.applicationContext.getBeanFactory().getAccessControlContext();
	}
	
	if (acc != null) {
		AccessController.doPrivileged(new PrivilegedAction<Object>() {
			@Override
			public Object run() {
				invokeAwareInterfaces(bean);
				return null;
			}
		}, acc);
	}
	else {
		// 根據實現對應的接口注入對應的組件
		invokeAwareInterfaces(bean);
	}
	
	return bean;
}

private void invokeAwareInterfaces(Object bean) {
	if (bean instanceof Aware) {
		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);
		}
		// 自定義組件實現ApplicationContextAware就可以在此處注入容器
		if (bean instanceof ApplicationContextAware) {
			((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
		}
	}
}

@Override
public Object postProcessAfterInitialization(Object bean, String beanName) {
	return bean;
}

2. InitDestroyAnnotationBeanPostProcessor： @PostConstruct和@PreDestroy的解析類；

3. AutowiredAnnotationBeanPostProcessor：@Autowired的解析類；