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Bean声明周期中的post-initialization和pre-destruction .

程序员文章站 2022-06-10 20:07:19
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在Bean的声明周期中,有两个事件尤为重要:post-initialization和pre-destruction。

Spring提供了两种机制:interface-based和method-based,供bean签入上述事件。

所谓的post-initialization和pre-destruction,是指在bean的属性设置完毕执行的事件和在bean销毁之前执行的事件。

method-based机制:通过在BeanFactory中的配置,init-method和destory-method,通过设置这两个属性来指定要执行的回调方法。

interface-based机制:bean需要实现InitializatingBean接口和DisposableBean接口。这两个接口分别拥有afterPropertiesSet()方法和destroy()方法。这两个方法在bean初始化后和销毁前被执行。效果与method-based机制等同。

 

以下是网上流传一个例子,我在eclipse中运行了一下

package com.test;
import javax.annotation.PostConstruct; 
import javax.annotation.PreDestroy; 

import org.springframework.beans.BeansException; 
import org.springframework.beans.factory.BeanFactory; 
import org.springframework.beans.factory.BeanFactoryAware; 
import org.springframework.beans.factory.BeanNameAware; 
import org.springframework.beans.factory.DisposableBean; 
import org.springframework.beans.factory.InitializingBean; 

public class LifeCycle implements BeanNameAware, BeanFactoryAware, InitializingBean, DisposableBean { 

public LifeCycle() { 
System.out.println("Constructor executing"); 
} 

private String cycle; 

public void setCycle(String cycle) { 
System.out.println("Setter methods executing"); 
this.cycle = cycle; 
} 

@Override 
public void setBeanName(String beanName) { 
System.out.println("BeanNameAware.setBeanName(String beanName) executing"); 
} 

@Override 
public void setBeanFactory(BeanFactory beanFactory) throws BeansException { 
System.out.println("BeanFactoryAware.setBeanFactory(BeanFactory beanFactory) executing"); 
} 

@PostConstruct 
public void beforeBeanConstructed() { 
System.out.println("BeanPostProcessor executing (before bean constructed)"); 
} 

@Override 
public void afterPropertiesSet() throws Exception { 
System.out.println("InitializingBean.afterPropertiesSet() executing"); 
} 

public void initMethod() { 
System.out.println("InitMethod executing"); 
} 

@PreDestroy 
public void afterBeanConstructed() { 
System.out.println("BeanPostProcessor executing (after bean constructed)"); 
} 

@Override 
public void destroy() throws Exception { 
System.out.println("DisposableBean.destroy() executing"); 
} 

public void destroyMethod() { 
System.out.println("DestroyMethod executing"); 
} 

} 

 

 

<?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="lifeCycle" class="com.test.LifeCycle" init-method="initMethod" destroy-method="destroyMethod"> 
		<property name="cycle" value="Life Cycle"/> 
		</bean> 
		
		<bean id="beanPostProcessor" class="org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor"> 
		<property name="initAnnotationType" value="javax.annotation.PostConstruct"/> 
		<property name="destroyAnnotationType" value="javax.annotation.PreDestroy"/> 
		</bean> 
	
	</beans>

 

package com.test;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.ClassPathResource;

public class LifeCycleDemo { 

	public static void main(String[] args) { 
	XmlBeanFactory factory = new XmlBeanFactory(new ClassPathResource("beans-config.xml")); 
	
	BeanPostProcessor bpp = (BeanPostProcessor)factory.getBean("beanPostProcessor"); 
	factory.addBeanPostProcessor(bpp); 
	
	LifeCycle lifeCycle = (LifeCycle)factory.getBean("lifeCycle"); 
	
	factory.destroySingleton("lifeCycle"); 
	} 

}

 

 

最后运行结果是:
Constructor executing
Setter methods executing
BeanNameAware.setBeanName(String beanName) executing
BeanFactoryAware.setBeanFactory(BeanFactory beanFactory) executing
BeanPostProcessor executing (before bean constructed)
InitializingBean.afterPropertiesSet() executing
InitMethod executing
BeanPostProcessor executing (after bean constructed)
DisposableBean.destroy() executing
DestroyMethod executing

 注入Bean具体的实现:
具体的bean创建过程和依赖关系的注入在createBean中,这个方法在AbstractAutowireCapableBeanFactory中给出了实现:

protected Object createBean(String beanName, RootBeanDefinition
mergedBeanDefinition, Object[] args)
throws BeanCreationException {
 // Guarantee initialization of beans that the current one depends on.
 // 这里对取得当前bean的所有依赖bean,确定能够取得这些已经被确定的bean,如果没有被创建,那么这个createBean会被这些IOC
 // getbean时创建这些bean
 if (mergedBeanDefinition.getDependsOn() != null) {
  for (int i = 0; i < mergedBeanDefinition.getDependsOn().length; i++) {
   getBean(mergedBeanDefinition.getDependsOn()[i]);
  }
 }
 ........
 // 这里是实例化bean对象的地方,注意这个BeanWrapper类,是对bean操作的主要封装类
 if (instanceWrapper == null) {
  instanceWrapper = createBeanInstance(beanName, mergedBeanDefinition,args);
 }
 Object bean = instanceWrapper.getWrappedInstance();
 ......
 //这个populate方法,是对已经创建的bean实例进行依赖注入的地方,会使用到在loadBeanDefinition的时候得到的那些propertyValue来对bean进行注入。
 if (continueWithPropertyPopulation) {
  populateBean(beanName, mergedBeanDefinition, instanceWrapper);
 }
 //这里完成客户自定义的对bean的一些初始化动作
 Object originalBean = bean;
 bean = initializeBean(beanName, bean, mergedBeanDefinition);
 // Register bean as disposable, and also as dependent on specified "dependsOn"beans.
 registerDisposableBeanIfNecessary(beanName, originalBean,mergedBeanDefinition);
 return bean;
}
.........
}