spring-BeanPostProcessor

BeanPostProcessor是spring框架提供的一个扩展点。

通过实现这个接口，程序员可插手bean实例化的过程。且这个接口可以设置多个，会形成一个列表，依次执行。

AOP正是通过BeanPostProcessor和IOC容器建立起了联系。

public interface BeanPostProcessor {

    default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

    default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

}

它有两个方法postProcessBeforeInitialization,postProcessAfterInitialization。
分别在bean初始化之前和之后执行。
执行顺序如下：
1，首先执行bean的构造方法,
2，BeanPostProcessor的postProcessBeforeInitialization方法
3，InitializingBean的afterPropertiesSet方法
4，initMethod方法
5，BeanPostProcessor的postProcessAfterInitialization方法

示例：

package com.test2;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

@Configuration
@ComponentScan("com.test2")
public class AppConfig {
}

package com.test2;

import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;

@Component
public class Bean1 {

    public Bean1(){
        System.out.println("Bean1 构造");
    }

    @PostConstruct
    public void init(){
        System.out.println("Bean1 init");
    }
}

package com.test2;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.core.PriorityOrdered;
import org.springframework.stereotype.Component;

@Component
public class MyBeanPostProcessor implements BeanPostProcessor,PriorityOrdered {

    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println(beanName + " postProcessAfterInitialization");

        return bean;
    }

    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println(beanName + " postProcessBeforeInitialization");

        return bean;
    }

    public int getOrder() {
        return 11; //值越小越先执行
    }
}

package com.test2;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.core.PriorityOrdered;
import org.springframework.stereotype.Component;

@Component
public class MyBeanPostProcessor1 implements BeanPostProcessor,PriorityOrdered {

    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println(beanName + " postProcessAfterInitialization1");

        return bean;
    }

    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println(beanName + " postProcessBeforeInitialization1");

        return bean;
    }

    public int getOrder() {
        return 10;
    }
}

package com.test2;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class MyTest {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext context =
                new AnnotationConfigApplicationContext(AppConfig.class);
        System.out.println(context.getBean("bean1"));

    }
}

执行结果：

appConfig postProcessBeforeInitialization1
appConfig postProcessBeforeInitialization
appConfig postProcessAfterInitialization1
appConfig postProcessAfterInitialization
Bean1 构造
bean1 postProcessBeforeInitialization1
bean1 postProcessBeforeInitialization
Bean1 init
bean1 postProcessAfterInitialization1
bean1 postProcessAfterInitialization
com.test2.Bean1@6e38921c