Spring（十二）：IOC容器中Bean的生命周期方法

IOC容器中Bean的生命周期方法

1）Spring IOC容器可以管理Bean的声明周期，Spring允许在Bean生命周期的特定点执行定制的任务。

2）Spring IOC容器对Bean的生命周期进行管理的过程：

--- 通过构造器或工厂方法创建Bean实例；

--- 为Bean的属性设置值和对其他Bean的引用；

--- Bean可以使用

--- 当容器关闭是，调用Bean的销毁方法

3）在Bean的声明里设置init-method和destroy-method属性，为Bean指定初始化和销毁方法。

演示：

第一步：创建一个Java Project，并导入以下包：

第二步：在src下添加com.dx.spring.beans.cycle.Member.java和spring bean配置文件bean-cycle.xml

Member.java

package com.dx.spring.beans.cycle;

public class Member {
    public Member() {
        System.out.println("Member constructor ... ");
    }

    private String name;

    public void setName(String name) {
        System.out.println("setName " + name);
        this.name = name;
    }

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

    public void destroyMethod() {
        System.out.println("despose method");
    }
}

注意：Member中的initMethod和destroyMethod两个方法名字是任意的。

bean-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="member" class="com.dx.spring.beans.cycle.Member" init-method="initMethod" destroy-method="destroyMethod">
        <property name="name" value="member1"></property>
    </bean>
</beans>

第三步：使用IOC容器管理Bean并关闭IOC容器查看打印日志：

package com.dx.spring.beans.cycle;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Main {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("bean-cycle.xml");
        
        Member member = (Member) ctx.getBean("member");
        System.out.println(member);

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

打印信息如下：

信息: Loading XML bean definitions from class path resource [bean-cycle.xml]
Member constructor ... 
setName member1
init method
com.dx.spring.beans.cycle.Member@4f7d0008
May 24, 2018 9:41:33 PM org.springframework.context.support.ClassPathXmlApplicationContext doClose
信息: Closing org.springframework.context.support.ClassPathXmlApplicationContext@4bf558aa: startup date [Thu May 24 21:41:33 CST 2018]; root of context hierarchy
despose method

创建Bean后置处理器

1）Bean后置处理器允许在调用初始化方法前后对Bean进行额外的处理；

2）Bean后置处理器对IOC容器里的所有Bean实例逐一进行处理，而非单一实例。其经典应用是：检查Bean属性的正确性或根据特定的标准更改Bean的属性。

3）对Bean后置处理器而言，需要实现abstract interface org.springframework.beans.factory.config.BeanPostProcessor抽象接口。在初始化方法被调用前后，Spring将把每个Bean实例分别传递给上述接口的以下两个方法：

演示：

第一步：添加com.dx.spring.beans.cycle.MyBeanPostProcessor.java使其实现抽象接口类BeanPostProcessor

package com.dx.spring.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:" + beanName + "," + bean);
        return BeanPostProcessor.super.postProcessBeforeInitialization(bean, beanName);
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("postProcessAfterInitialization" + beanName + "," + bean);
        return BeanPostProcessor.super.postProcessAfterInitialization(bean, beanName);
    }
}

第二步：修改spring-cycle.xml配置文件

<?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="member" class="com.dx.spring.beans.cycle.Member" init-method="initMethod" destroy-method="destroyMethod">
        <property name="name" value="member1"></property>
    </bean>
    <!-- 注意：这里不需要指定id -->
    <bean class="com.dx.spring.beans.cycle.MyBeanPostProcessor"></bean>
</beans>

第三步：执行Main测试，查看打印信息：

信息: Loading XML bean definitions from class path resource [bean-cycle.xml]
Member constructor ... 
setName member1
postProcessBeforeInitialization:member,com.dx.spring.beans.cycle.Member@1a968a59
init method
postProcessAfterInitializationmember,com.dx.spring.beans.cycle.Member@1a968a59
com.dx.spring.beans.cycle.Member@1a968a59
May 24, 2018 9:46:07 PM org.springframework.context.support.ClassPathXmlApplicationContext doClose
信息: Closing org.springframework.context.support.ClassPathXmlApplicationContext@4bf558aa: startup date [Thu May 24 21:46:06 CST 2018]; root of context hierarchy
despose method