spring之aware接口

实现org.springframework.beans.factory.aware子接口的Bean类在创建时会在调用该bean的init方法之前调用aware子接口的相应方法，举几个类来说明下：

org.springframework.context.ApplicationContextAware的setApplicationContext方法

org.springframework.beans.factory.BeanFactoryAware的setBeanFactory(BeanFactory beanFactory)方法等

通过实现ApplicationContextAware接口，我们就能获取到当前运行的ApplicationContext对象，通过实现BeanFactoryAware接口就能获取到当前系统使用的BeanFactory对象。

但是aware子接口是怎么被调用的呢？这就需要涉及到bean的创建过程中的一个环节：

1.先看org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory类的方法：

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


2.这里会通过getBeanPostProcessors方法获取该BeanFactory对象具体支持的所有BeanPostProcessor，这里用到了java的多态特性，这里以
org.springframework.beans.factory.support.DefaultListableBeanFactory类为例来讲述该类默认提供的BeanPostProcessors如下（所以由DefaultListableBeanFactory类创建的bean对象都要经历这些BeanPostProcessor的摧残）：
[org.springframework.context.support.ApplicationContextAwareProcessor, org.springframework.context.support.PostProcessorRegistrationDelegate$BeanPostProcessorChecker, org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor, org.springframework.context.annotation.ConfigurationClassPostProcessor$EnhancedConfigurationBeanPostProcessor,
org.springframework.context.annotation.CommonAnnotationBeanPostProcessor, org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor, org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor, org.springframework.context.support.ApplicationListenerDetector]
3.接下来以ApplicationContextAwareProcessor类为例来讲述该类的postProcessBeforeInitialization方法：
@Overridepublic 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>() {@Overridepublic Object run() {invokeAwareInterfaces(bean);return null;}}, acc);}else {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);}if (bean instanceof ApplicationContextAware) {((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);}}}


所以想要获取ApplicationContext对象，可以通过实现ApplicationContextAware接口，并实现setApplicationContext接口来获取。
至于DefaultListableBeanFactory类中的其他的BeanPostProcessor感兴趣的小伙伴可以自行查看