Spring源码窥探之：扩展原理BeanFactoryPostProcessor

BeanPostPorcessor是在bean创建对象初始化前后进行拦截工作,而BeanFactoryPostProcessor是Bean工厂的后置处理器,在Bean定义加载完成之后，Bean实例初始化之前会调用postProcessBeanFactory方法.
1.实现类

public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        int count = beanFactory.getBeanDefinitionCount();
        String[] beanDefinitionNames = beanFactory.getBeanDefinitionNames();
        for (String str : beanDefinitionNames) {
            System.out.println("----->" + str);
        }
        System.out.println("获取容器中BeanDefinition的数量-------> " + count);
    }
}

2. 配置类,其中注入了一个实体类,跟一个MyBeanFactoryPostProcessor

/**
 * description
 *
 * @author 70KG
 * @date 2018/12/24
 */
@Configurationpublic class MyConfig {

    @Bean
    public People01 people01() {
        return new People01();
    }

    @Bean
    public MyBeanFactoryPostProcessor myBeanFactoryPostProcessor() {
        return new MyBeanFactoryPostProcessor();
    }

}

3. 测试类

public class Test01 {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext app = new AnnotationConfigApplicationContext(MyConfig.class);
    }

}

4. 结果,可见postProcessBeanFactory方法先于构造方法执行

----->org.springframework.context.annotation.internalConfigurationAnnotationProcessor
----->org.springframework.context.annotation.internalAutowiredAnnotationProcessor
----->org.springframework.context.annotation.internalRequiredAnnotationProcessor
----->org.springframework.context.annotation.internalCommonAnnotationProcessor
----->org.springframework.context.event.internalEventListenerProcessor
----->org.springframework.context.event.internalEventListenerFactory
----->myConfig
----->people01
----->myBeanFactoryPostProcessor
获取容器中BeanDefinition的数量-------> 9
People01无参构造执行...

BeanFactoryPostProcessor调用栈:
1. AnnotationConfigApplicationContext类中AnnotationConfigApplicationContext构造中的refresh().尝试去刷新容器
2. AbstractApplicationContext类中refresh()方法的invokeBeanFactoryPostProcessors(beanFactory).
在初始化实例之前,首先对BeanFactory进行后置处理,目的就是为了在所有的Bean定义都已经加载,但还未初始化之前,向容器中
增加属性或者重写Bean的定义信息(This allows for overriding or adding properties even to eager-initializing beans)
3. AbstractApplicationContext类中invokeBeanFactoryPostProcessors()方法中的PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors())
4. PostProcessorRegistrationDelegate类中的invokeBeanFactoryPostProcessors()方法中的invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory)
5. PostProcessorRegistrationDelegate类中的invokeBeanFactoryPostProcessors()方法中的postProcessor.postProcessBeanFactory(beanFactory)进行回调.