spring中的BeanPostProcessor

r囧r小猫 2022-05-16 09:07 256阅读 0赞

/**
     *   实现BeanPostProcessor的类常用功能都有哪些
     *      InitDestroyAnnotationBeanPostProcessor：init和destroy方法的后处理，包括@PostConstruct和@PreDestroy注解
     *      AutowiredAnnotationBeanPostProcessor：处理含有@Autowired注解的参数注入
     *      ApplicationContextAwareProcessor：处理postProcessBeforeInitialization方法
     *      AsyncAnnotationBeanPostProcessor：处理@Async注解
     *      BeanValidationPostProcessor：参数校验
     *
     */

类实现BeanPostProcessor接口，并重写postProcessBeforeInitialization和postProcessAfterInitialization方法，将类注册到IOC容器中，这两个方法会在每一个组建被创建时都被调用

postProcessBeforeInitialization：在构造方法之后，初始化方法执行之前被调用

postProcessAfterInitialization：在初始化方法执行之后被调用

下面是具体的代码

import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.config.BeanPostProcessor;
    import org.springframework.stereotype.Component;
    
    @Component
    public class MyBeanPostProcessor implements BeanPostProcessor {
    
        //bean是当前组建，beanName是当前组建在容器中的id
        @Override
        public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
            System.out.println("postProcessBeforeInitialization->" + bean + "->" + beanName);
            return bean;
        }
    
        @Override
        public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
            System.out.println("postProcessAfterInitialization->" + bean + "->" + beanName);
            return bean;
        }
    }

当这个容器被注册到容器中时，方法被调用的顺序如下面

**Construct->postProcessBeforeInitialization->Init->postProcessAfterInitialization->Destroy**

### **原理：** ###

下面是源码中调用方法的顺序：

/**
         * populateBean（实例化bean并为其赋值）
         * {
         *     applyBeanPostProcessorsBeforeInitialization
         *     invokeInitMethods（反射调用初始化方法）
         *     applyBeanPostProcessorsAfterInitialization
         * }
         */