MichaelFreeman

spring framework 常用接口介绍

Spring加载全过程

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BeanPostProcessor

接口定义

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/**
* Apply this BeanPostProcessor to the given new bean instance <i>before</i> any bean
* initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
* or a custom init-method). The bean will already be populated with property values.
* The returned bean instance may be a wrapper around the original.
* @param bean the new bean instance
* @param beanName the name of the bean
* @return the bean instance to use, either the original or a wrapped one; if
* {@code null}, no subsequent BeanPostProcessors will be invoked
* @throws org.springframework.beans.BeansException in case of errors
* @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
*/
Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;

/**
* Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean
* initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
* or a custom init-method). The bean will already be populated with property values.
* The returned bean instance may be a wrapper around the original.
* <p>In case of a FactoryBean, this callback will be invoked for both the FactoryBean
* instance and the objects created by the FactoryBean (as of Spring 2.0). The
* post-processor can decide whether to apply to either the FactoryBean or created
* objects or both through corresponding {@code bean instanceof FactoryBean} checks.
* <p>This callback will also be invoked after a short-circuiting triggered by a
* {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
* in contrast to all other BeanPostProcessor callbacks.
* @param bean the new bean instance
* @param beanName the name of the bean
* @return the bean instance to use, either the original or a wrapped one; if
* {@code null}, no subsequent BeanPostProcessors will be invoked
* @throws org.springframework.beans.BeansException in case of errors
* @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
* @see org.springframework.beans.factory.FactoryBean
*/
Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;

执行顺序

  • org.springframework.beans.factory.config.BeanPostProcessor#postProcessBeforeInitialization
  • org.springframework.beans.factory.InitializingBean#afterPropertiesSet
  • org.springframework.beans.factory.config.BeanPostProcessor#postProcessAfterInitialization

ApplicationListener

接口定义

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public interface ApplicationListener<E extends ApplicationEvent> extends EventListener {

/**
* Handle an application event.
* @param event the event to respond to
*/
void onApplicationEvent(E event);

}

ApplicationEvent

  • ContextRefreshedEvent:ApplicationContext容器初始化或刷新时触发该事件。此处的初始化是指:所有的Bean被成功装载,后处理Bean被检测并激活,所有Singleton Bean 被预实例化,ApplicationContext容器已就绪可用

  • ContextStartedEvent:当使用ConfigurableApplicationContext(ApplicationContext的子接口)接口的start()方法启动ApplicationContext容器时触发该事件。容器管理声明周期的Bean实例将获得一个指定的启动信号,这在经常需要停止后重新启动的场合比较常见

  • ContextClosedEvent:当使用ConfigurableApplicationContext接口的close()方法关闭ApplicationContext时触发该事件

  • ContextStoppedEvent:当使用ConfigurableApplicationContext接口的stop()方法使ApplicationContext容器停止时触发该事件。此处的停止,意味着容器管理生命周期的Bean实例将获得一个指定的停止信号,被停止的Spring容器可再次调用start()方法重新启动

  • RequestHandledEvent:Web相关事件,只能应用于使用DispatcherServlet的Web应用。在使用Spring作为前端的MVC控制器时,当Spring处理用户请求结束后,系统会自动触发该事件。

  • Event也可以自定义实现

ApplicationContextAware

为何实现ApplicationContextAware可以获取到ApplicationContext?

其实是org.springframework.context.support.ApplicationContextAwareProcessor实现BeanPostProcessor进行处理。

源码如下:

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class ApplicationContextAwareProcessor implements BeanPostProcessor {

private final ConfigurableApplicationContext applicationContext;

private final StringValueResolver embeddedValueResolver;


/**
* Create a new ApplicationContextAwareProcessor for the given context.
*/
public ApplicationContextAwareProcessor(ConfigurableApplicationContext applicationContext) {
this.applicationContext = applicationContext;
this.embeddedValueResolver = new EmbeddedValueResolver(applicationContext.getBeanFactory());
}


@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);
}
}
}

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

}