spring之aware接口
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：
@Override
public 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：
@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 {
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
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