Spring容器中Bean的生命周期

Spring 容器中的 Bean 是有生命周期的，Spring 允许 Bean 在初始化完成后以及销毁前执行特定的操作。下面是常用的三种指定特定操作的方法：

通过实现InitializingBean/DisposableBean 接口来定制初始化之后/销毁之前的操作方法；
通过<bean> 元素的 init-method/destroy-method属性指定初始化之后 /销毁之前调用的操作方法；
在指定方法上加上@PostConstruct或@PreDestroy注解来制定该方法是在初始化之后还是销毁之前调用。

这几种配置方式，执行顺序是怎样的呢？我们通过例子来研究下：

Java类：

[java] view
plain copy

import javax.annotation.PostConstruct;

import javax.annotation.PreDestroy;

import org.springframework.beans.factory.DisposableBean;

import org.springframework.beans.factory.InitializingBean;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class InitAndDestroySeqBean implements InitializingBean,DisposableBean {

public InitAndDestroySeqBean(){

System.out.println("执行InitAndDestroySeqBean: 构造方法");

}

@PostConstruct

public void postConstruct() {

System.out.println("执行InitAndDestroySeqBean: postConstruct");

}

@Override

public void afterPropertiesSet() throws Exception {

System.out.println("执行InitAndDestroySeqBean: afterPropertiesSet");

}

public void initMethod() {

System.out.println("执行InitAndDestroySeqBean: init-method");

}

@PreDestroy

public void preDestroy() {

System.out.println("执行InitAndDestroySeqBean: preDestroy");

}

@Override

public void destroy() throws Exception {

System.out.println("执行InitAndDestroySeqBean: destroy");

}

public void destroyMethod() {

System.out.println("执行InitAndDestroySeqBean: destroy-method");

}

public static void main(String[] args) {

ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("com/chj/spring/bean.xml");

context.close();

}

}

Spring配置文件：

[html] view
plain copy

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd">
<context:annotation-config/>

<bean id="initAndDestroySeqBean" class="com.chj.spring.InitAndDestroySeqBean" init-method="initMethod" destroy-method="destroyMethod"/>

</beans>

运行InitAndDestroySeqBean的main方法，结果如下：

[html] view
plain copy

2013-03-03 17:11:19,098 DEBUG support.DefaultListableBeanFactory - Creating instance of bean 'initAndDestroySeqBean'

执行InitAndDestroySeqBean: 构造方法

2013-03-03 17:11:19,114 DEBUG annotation.CommonAnnotationBeanPostProcessor - Found init method on class [com.alibaba.chj.spring.InitAndDestroySeqBean]: public void com.alibaba.chj.spring.InitAndDestroySeqBean.postConstruct()

2013-03-03 17:11:19,114 DEBUG annotation.CommonAnnotationBeanPostProcessor - Found destroy method on class [com.alibaba.chj.spring.InitAndDestroySeqBean]: public void com.alibaba.chj.spring.InitAndDestroySeqBean.preDestroy()

2013-03-03 17:11:19,129 DEBUG support.DefaultListableBeanFactory - Eagerly caching bean 'initAndDestroySeqBean' to allow for resolving potential circular references

2013-03-03 17:11:19,129 DEBUG annotation.CommonAnnotationBeanPostProcessor - Invoking init method on bean 'initAndDestroySeqBean': public void com.alibaba.chj.spring.InitAndDestroySeqBean.postConstruct()

执行InitAndDestroySeqBean: postConstruct

2013-03-03 17:11:19,129 DEBUG support.DefaultListableBeanFactory - Invoking afterPropertiesSet() on bean with name 'initAndDestroySeqBean'

执行InitAndDestroySeqBean: afterPropertiesSet

2013-03-03 17:11:19,129 DEBUG support.DefaultListableBeanFactory - Invoking init method 'initMethod' on bean with name 'initAndDestroySeqBean'

执行InitAndDestroySeqBean: init-method

2013-03-03 17:11:19,129 DEBUG support.DefaultListableBeanFactory - Finished creating instance of bean 'initAndDestroySeqBean'

2013-03-03 17:11:19,129 INFO support.ClassPathXmlApplicationContext - Closing org.springframework.context.support.ClassPathXmlApplicationContext@56a499: display name [org.springframework.context.support.ClassPathXmlApplicationContext@56a499]; startup date [Sun Mar 03 17:11:17 CST 2013]; root of context hierarchy

2013-03-03 17:11:19,129 INFO support.DefaultListableBeanFactory - Destroying singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@1292d26: defining beans [org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,initAndDestroySeqBean]; root of factory hierarchy

2013-03-03 17:11:19,129 DEBUG annotation.CommonAnnotationBeanPostProcessor - Invoking destroy method on bean 'initAndDestroySeqBean': public void com.alibaba.chj.spring.InitAndDestroySeqBean.preDestroy()

执行InitAndDestroySeqBean: preDestroy

2013-03-03 17:11:19,145 DEBUG support.DisposableBeanAdapter - Invoking destroy() on bean with name 'initAndDestroySeqBean'

执行InitAndDestroySeqBean: destroy

2013-03-03 17:11:19,145 DEBUG support.DisposableBeanAdapter - Invoking destroy method 'destroyMethod' on bean with name 'initAndDestroySeqBean'

执行InitAndDestroySeqBean: destroy-method

从执行结果可以看出：

Bean在实例化的过程中：Constructor > @PostConstruct >InitializingBean > init-method

Bean在销毁的过程中：@PreDestroy > DisposableBean > destroy-method