Spring BeanPostProcessor 代码实践

Bean后置处理器接口，在初始化方法前后执行，允许对新建的Bean实例进行自定义修改，如检查标记接口或者包装为代理类。

源码

package org.springframework.beans.factory.config;

import org.springframework.beans.BeansException;
import org.springframework.lang.Nullable;

public interface BeanPostProcessor {

	/**
	 * 在属性填充完成之后,初始化方法（afterPropertiesSet 或者 @PostConstruct）之前执行。
	 */
	@Nullable
	default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}

	/**
	 * 初始化方法之后之前执行。
	 */
	@Nullable
	default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}

}

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执行时机

在Bean实例创建并完成属性填充之后，调用AbstractAutowireCapableBeanFactory的initializeBean方法初始化Bean。在初始化前后分别执行了 postProcessBeforeInitialization 和 postProcessAfterInitialization 方法。

代码实践

新建一个BeanPostProcessor实例

/**
 * 对所有Spring管理的Bean都有效
 * */
@Slf4j
@Component
public class MyBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        log.info("执行 BeanPostProcessor.postProcessBeforeInitialization 方法, beanName=>{}", bean, beanName);
        return BeanPostProcessor.super.postProcessBeforeInitialization(bean, beanName);
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        log.info("执行 BeanPostProcessor.postProcessAfterInitialization 方法, beanName=>{}", bean, beanName);
        return BeanPostProcessor.super.postProcessAfterInitialization(bean, beanName);
    }
}

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新建一个Spring Component类，并实现依赖注入和初始化方法

@Slf4j
@Component
public class BeanPostProcessorDemo implements InitializingBean {

    private AnotherComponent anotherComponent;

    @Autowired
    public void setAnotherComponent(AnotherComponent anotherComponent) {
        log.info("执行依赖注入");
        this.anotherComponent = anotherComponent;
    }

    @PostConstruct
    public void init(){
        log.info("执行 @PostConstruct 标注的方法");
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        log.info("执行 InitializingBean.afterPropertiesSet 方法");
    }

}

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运行结果

执行顺序为：依赖注入 > postProcessBeforeInitialization > @PostConstruct > afterPropertiesSet > postProcessAfterInitialization

注：BeanPostProcessor默认是会对整个Spring容器中所有的bean进行处理。