【Spring】09 Bean的生命周期-优快云博客

本文链接：https://blog.youkuaiyun.com/ZyhMemory/article/details/88579551

本文深入解析Spring框架中Bean的生命周期，包括构造函数初始化、属性设置、自定义初始化方法、依赖注入、后置处理器操作及销毁过程。通过示例代码展示如何配置Bean的初始化和销毁方法，以及BeanPostProcessor在初始化过程中的作用。

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Bean的生命周期

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beans-cycle.xml

<?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.xsd">

    <bean id="car" class="com.test.sping.beans.cycle.Car"
        init-method="init" destroy-method="destroy">
        <property name="brand" value="Aodi"></property>
    </bean>

</beans>

Car.java(com.test.sping.beans.cycle.Car)

package com.test.sping.beans.cycle;

public class Car {

    public Car() {
        System.out.println("Car's Constructor...");
    }

    private String brand;

    public void setBrand(String brand) {
        System.out.println("setBrand...");
        this.brand = brand;
    }

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

    public void destroy() {
        System.out.println("destroy...");
    }

    @Override
    public String toString() {
        return "Car{" +
                "brand='" + brand + '\'' +
                '}';
    }
}

Main.java(com.test.sping.beans.cycle.Main)

package com.test.sping.beans.cycle;


import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Main {

    public static void main(String[] args) {

        ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("beans-cycle.xml");

        Car car = (Car) ctx.getBean("car");
        System.out.println(car);

        // 关闭 IOC 容器
        ctx.close();
    }
}

Bean添加后置处理器的生命周期

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beans-cycle.xml

<?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.xsd">

    <bean id="car" class="com.test.sping.beans.cycle.Car"
        init-method="init" destroy-method="destroy">
        <property name="brand" value="Aodi"></property>
    </bean>

    <!--
        实现 BeanPostProcessor 接口，并具体提供
        Object postProcessBeforeInitialization(Object bean, String beanName)：init-method 之前被调用
        Object postProcessAfterInitialization(Object bean, String beanName)：init-method 之后被调用
        的实现

        bean：bean 实例本身
        beanName：IOC 容器配置的 bean 的名字。
        返回值：是实际上返回给用户的那个 Bean，注意：可以在以上俩个方法中修改返回的 bean，甚至返回一个新的 bean
    -->
    <!-- 配置 bean 的后置处理器：不需要配置 id，IOC 容器自动识别是一个 BeanPostProcessor -->
    <bean class="com.test.sping.beans.cycle.MyBeanPostProcessor"></bean>

</beans>

MyBeanPostProcessor.java(com.test.sping.beans.cycle.MyBeanPostProcessor)

package com.test.sping.beans.cycle;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;

public class MyBeanPostProcessor implements BeanPostProcessor {

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

        if ("car".equals(beanName)){
            // ...
        }

        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException{
        System.out.println("postProcessAfterInitialization：" + bean + "," + beanName);
        Car car = new Car();
        car.setBrand("Ford");
        return car;
    }

}