也路Spring Bean的生命周期

也谈Spring Bean的生命周期

插叙一下，记得某个博文中提到：“Spring的Bean容器只管理非单例Bean的生命周期，单例Bean的生命周期不在管理范围内”，其实我认为这句话恰好说反了。首先明确一点，并非Spring容器中所有的Bean都有生命周期行为，只有接受容器管理生命周期的Bean才具有生命周期行为：而单例（Singleton）Bean接受容器管理，非单例（non-singleton）Bean在实例化后，完全交给了客户端代码管理，容器不再跟踪其生命周期，每次客户请求，容器都会创建一个新的实例，所以Spring容易无法知晓Bean何时销毁。

继续刚才的话题——Bean容器的生命周期。其实上图有个节点没有画出，就是在实例化所有Bean之前会执行BeanFactoryPostProcessors。不过也不care，因为这和Bean的生命周期没有太大关系，所以没有提及也属正常，权且忽略该节点。

从图中，我们可以看到实例化Bean的过程中有以下几个节点：

1）设置属性值；

2）调用Bean中的BeanNameAware.setBeanName()方法，如果该Bean实现了BeanNameAware接口；

3）调用Bean中的BeanFactoryAware.setBeanFactory()方法，如果该Bean实现了BeanFactoryAware接口；

4）调用BeanPostProcessors.postProcessBeforeInitialization()方法；

5）调用Bean中的afterPropertiesSet方法，如果该Bean实现了InitializingBean接口；

6）调用Bean中的init-method，通常是在配置bean的时候指定了init-method，例如：<bean class="beanClass"init-method="init"></bean>

7）调用BeanPostProcessors.postProcessAfterInitialization()方法；

8）如果该Bean是单例的，则当容器销毁并且该Bean实现了DisposableBean接口的时候，调用destory方法；如果该Bean是prototype，则将准备好的Bean提交给调用者，后续不再管理该Bean的生命周期。

好了，简单了描述了下那幅图。一切都还太抽象了，作为程序员，代码还是最直接的表达方式。那我们就一起看段演示代码吧。

首先，为达到演示效果，我们准备两个待测试的Bean，代码如下：

Java代码 ?

@Component??public?class?DemoBean?implements?BeanFactoryAware,?BeanNameAware,??????????InitializingBean,?DisposableBean?{??????@PostConstruct??????public?void?init()?{?????????System.out.println("DemoBean:?init-method");??????}??????public?void?destroy()?throws?Exception?{?????????System.out.println("DemoBean:?destroy-method!");??????}??????public?void?afterPropertiesSet()?throws?Exception?{?????????System.out.println("DemoBean:?after?properties?set!");??????}??????public?void?setBeanName(String?name)?{?????????System.out.println("DemoBean:?beanName?aware,?[name="?+?name?+?"]");??????}??????public?void?setBeanFactory(BeanFactory?beanFactory)?throws?BeansException?{?????????System.out.println("DemoBean:?beanFactory?aware,?[beanFactory="?+?beanFactory.toString()?+?"]");??????}??}??

Java代码 ?

public?class?AnotherDemoBean?implements?InitializingBean?{?????????@PostConstruct??????public?void?postConstruct()?{?????????System.out.println("AnotherDemoBean:?postConstruct-method");??????}????????public?void?init()?{?????????System.out.println("AnotherDemoBean:?init-method");??????}??????@Override??????public?void?afterPropertiesSet()?throws?Exception?{?????????System.out.println("AnotherDemoBean:?after?properties?set!");??????}??}???

上面两个Bean大致相同，区别在于第一个Bean使用注解方式注入，第二个Bean我们使用配置文件方式，并指定其init-method，用于观察init-method与postConstruct的执行先后。

我们这个演示Bean实现了BeanFactoryAware, BeanNameAware, InitializingBean,?DisposableBean这几个接口，其实这些接口也可理解为Spring容器的一个个扩展点。

然后，我们再编写一个BeanPostProcessor，用于演示生命周期中的步骤4和步骤7。?代码如下：

Java代码 ?

@Component??public?class?DemoBeanPostProcessor?implements?BeanPostProcessor?{??????public?Object?postProcessBeforeInitialization(Object?bean,?String?beanName)?throws?BeansException?{?????????System.out.println("DemoBeanPostProcessor:?post?process?before?initialization,?[beanName="?+?beanName?+?",?bean="?+?bean?+?"]");?????????return?bean;??????}??????public?Object?postProcessAfterInitialization(Object?bean,?String?beanName)?throws?BeansException?{?????????System.out.println("DemoBeanPostProcessor:?post?process?before?initialization,?[beanName="?+?beanName?+?",?bean="?+?bean?+?"]");?????????return?bean;??????}??}??

最后，我们编写测试类，以及Spring的配置文件，这里我们使用ClassPathXMLApplicationContext加载配置文件和初始化Spring容器。一起看下配置文件和测试类代码：

applicationContext.xml:

Xml代码 ?

<?xml?version="1.0"?encoding="GBK"?>?????<beans?xmlns="http://www.springframework.org/schema/beans"??????xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"?xmlns:aop="http://www.springframework.org/schema/aop"??????xmlns:context="http://www.springframework.org/schema/context"?xmlns:tx="http://www.springframework.org/schema/tx"??????xsi:schemaLocation="??????????http://www.springframework.org/schema/beans?http://www.springframework.org/schema/beans/spring-beans-2.5.xsd??????????http://www.springframework.org/schema/aop?http://www.springframework.org/schema/aop/spring-aop-2.5.xsd??????????http://www.springframework.org/schema/context?http://www.springframework.org/schema/context/spring-context-2.5.xsd??????????http://www.springframework.org/schema/tx?http://www.springframework.org/schema/tx/spring-tx-2.5.xsd">??????<context:component-scan?base-package="com.shansun.multidemo"></context:component-scan>??????<bean?class="com.shansun.multidemo.spring.lifecycle.AnotherDemoBean"?init-method="init"></bean>??</beans>??

Main.java

Java代码 ?

public?class?Main?{??????@SuppressWarnings("unused")??????public?static?void?main(String[]?args)?{??????????ApplicationContext?ctx?=?new?ClassPathXmlApplicationContext("applicationContext.xml");??????}??}??

好了，一切就绪，我们就静观程序输出吧：

Java代码 ?

DemoBean:?beanName?aware,?[name=demoBean]??DemoBean:?beanFactory?aware,?[beanFactory=org.springframework.beans.factory.support.DefaultListableBeanFactory@888e6c:defining?beans?[demoBean,demoBeanFactoryPostProcessor,demoBeanPostProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,com.shansun.multidemo.spring.lifecycle.AnotherDemoBean#0];?root?of?factory?hierarchy]??DemoBean:?init-method??DemoBeanPostProcessor:?post?process?before?initialization,?[beanName=demoBean,?bean=com.shansun.multidemo.spring.lifecycle.DemoBean@1deeb40]??DemoBean:?after?properties?set!??DemoBeanPostProcessor:?post?process?before?initialization,?[beanName=demoBean,?bean=com.shansun.multidemo.spring.lifecycle.DemoBean@1deeb40]??AnotherDemoBean:?postConstruct-method??DemoBeanPostProcessor:?post?process?before?initialization,?[beanName=com.shansun.multidemo.spring.lifecycle.AnotherDemoBean#0,?bean=com.shansun.multidemo.spring.lifecycle.AnotherDemoBean@1a7ddcf]??AnotherDemoBean:?after?properties?set!??AnotherDemoBean:?init-method??DemoBeanPostProcessor:?post?process?before?initialization,?[beanName=com.shansun.multidemo.spring.lifecycle.AnotherDemoBean#0,?bean=com.shansun.multidemo.spring.lifecycle.AnotherDemoBean@1a7ddcf]??

和我们预期的是否一样呢？是的。观察结果发现一个有趣的地方：在配置文件中指定的init-method和使用@PostConstruct注解的方法，孰先孰后呢，两者是否等同呢？后续我将通过分析源码给出结论。

我们通过演示代码也验证了Bean容器的生命周期，但是还缺点什么吧。对了，透过Spring源码讲述Bean容器的生命周期是否更加直观和令人信服呢？下面我们去Spring源码中一探究竟。这里我们选用的是spring-2.5.6.SEC02。

大家应该都知道Spring中BeanFactory和ApplicationContext的关系了吧，ApplicationContext继承自BeanFactory，所以可以操作到bean。更详细的内容可以参考许令波同学的《Spring框架的设计理念与设计模式分析》，里面有较清晰的分析。

好了，闲话不多说。

首先，我们探视下实例化Bean的方法initializeBean，该方法在org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory类下，一起看下该段代码：

Java代码 ?

protected?Object?initializeBean(String?beanName,?Object?bean,?RootBeanDefinition?mbd)?{???????????if?(bean?instanceof?BeanNameAware)?{?????????????????????((BeanNameAware)?bean).setBeanName(beanName);???????????}??????????????if?(bean?instanceof?BeanClassLoaderAware)?{?????????????????????((BeanClassLoaderAware)?bean).setBeanClassLoader(getBeanClassLoader());???????????}??????????????if?(bean?instanceof?BeanFactoryAware)?{?????????????????????((BeanFactoryAware)?bean).setBeanFactory(this);???????????}??????????????Object?wrappedBean?=?bean;???????????if?(mbd?==?null?||?!mbd.isSynthetic())?{?????????????????????wrappedBean?=?applyBeanPostProcessorsBeforeInitialization(wrappedBean,?beanName);???????????}??????????????try?{?????????????????????invokeInitMethods(beanName,?wrappedBean,?mbd);???????????}???????????catch?(Throwable?ex)?{?????????????????????throw?new?BeanCreationException(???????????????????????????????????????(mbd?!=?null???mbd.getResourceDescription()?:?null),???????????????????????????????????????beanName,?"Invocation?of?init?method?failed",?ex);???????????}??????????????if?(mbd?==?null?||?!mbd.isSynthetic())?{?????????????????????wrappedBean?=?applyBeanPostProcessorsAfterInitialization(wrappedBean,?beanName);???????????}???????????return?wrappedBean;??}??

这样够直观了吧，是不是和前文描述的一样呢，J

本文源代码下载：https://lb-multi-demo.googlecode.com/svn/trunk/spring-lifecycle-test

也路Spring Bean的生命周期

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