Spring----BeanPostProcessor（后置处理器）

文章目录

• 前言
• 一、BeanPostProcessor源码
• 案例

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前言

BeanPostProcessor 接口也被称为后置处理器，通过该接口可以自定义调用初始化前后执行的操作方法。

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一、BeanPostProcessor源码

public interface BeanPostProcessor {
    Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;
    Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;
}

• postProcessBeforeInitialization 在 Bean 实例化、依赖注入后，初始化前调用。
• postProcessAfterInitialization 在 Bean 实例化、依赖注入、初始化都完成后调用。

当需要添加多个后置处理器实现类时，默认情况下 Spring 容器会根据后置处理器的定义顺序来依次调用。也可以通过实现 Ordered 接口的 getOrder 方法指定后置处理器的执行顺序。该方法返回值为整数，默认值为 0，值越大优先级越低。

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案例

1.创建HelloWorld 类

public class HelloWorld {
    private String message;
    public void setMessage(String message) {
        this.message = message;
    }
    public void getMessage() {
        System.out.println("Message : " + message);
    }
    public void init() {
        System.out.println("Bean正在初始化");
    }
    public void destroy() {
        System.out.println("Bean将要被销毁");
    }
}

2.创建InitHelloWorldA 类

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.core.Ordered;
public class InitHelloWorldA implements BeanPostProcessor, Ordered {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("A Before : " + beanName);
        return bean;
    }
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("A After : " + beanName);
        return bean;
    }
    @Override
    public int getOrder() {
        return 5;
    }
}

3.创建InitHelloWorldB 类

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.core.Ordered;
public class InitHelloWorldB implements BeanPostProcessor, Ordered {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("B Before : " + beanName);
        return bean;
    }
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("B After : " + beanName);
        return bean;
    }
    @Override
    public int getOrder() {
        return 0;
    }
}

4.Beans.xml配置

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
    <bean id="helloWorld" class="net.biancheng.HelloWorld"
        init-method="init" destroy-method="destroy">
        <property name="message" value="Hello World！" />
    </bean>
    <!-- 注册处理器 -->
    <bean class="net.biancheng.InitHelloWorldA" />
    <bean class="net.biancheng.InitHelloWorldB" />
</beans>

5.创建MainApp 类

import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MainApp {
    public static void main(String[] args) {
        AbstractApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");
        HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
        obj.getMessage();
        context.registerShutdownHook();
    }
}

6.结果与总结

B Before : helloWorld
A Before : helloWorld
Bean正在初始化
B After : helloWorld
A After : helloWorld
Message : Hello World！
Bean将要被销毁

运行结果:postProcessBeforeInitialization 方法是在 Bean 实例化和依赖注入后，自定义初始化方法前执行的。而 postProcessAfterInitialization 方法是在自定义初始化方法后执行的。由于 getOrder 方法返回值越大，优先级越低，所以 InitHelloWorld2 先执行。