Spring中的DisposableBean和InitializingBean，ApplicationContextAware的用法

Spring中的DisposableBean和InitializingBean，ApplicationContextAware的用法

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categories: Spring

Spring中的DisposableBean和InitializingBean的用法

在spring容器初始化bean和销毁bean的以前的操作有很多种，
　　目前我知道的有：在xml中定义的时候用init-method和destory-method，还有一种就是定义bean的时候实现DisposableBean和InitializingBean 这两个接口，打开InitializingBean 的源码：

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public interface InitializingBean {

    /**
     * Invoked by a BeanFactory after it has set all bean properties supplied
     * (and satisfied BeanFactoryAware and ApplicationContextAware).
     * <p>This method allows the bean instance to perform initialization only
     * possible when all bean properties have been set and to throw an
     * exception in the event of misconfiguration.
     * @throws Exception in the event of misconfiguration (such
     * as failure to set an essential property) or if initialization fails.
     */
    void afterPropertiesSet() throws Exception;

}

根据注解很清楚的可以看出，afterPropertiesSet()表示在资源加载完以后，初始化bean之前执行的方法，我猜想spring底层应该会在初始化bean的时候，应该会使用（bean instanceof InitializingBean）判断是不是实现了这个接口，其实在很多框架中都是这么干的，但是因为没研究过spring源码，暂且还不知道底层原理。这样我们就可以在初始化的时候，做一些自己想要做的事了。
　　同理，DisposableBean就是在一个bean被销毁的时候，spring容器会帮你自动执行这个方法，估计底层原理也是差不多的，对于一些使用完之后需要释放资源的bean，我们都会实现这个接口，或者是配置destory-method方法。源码也基本是相似的，只是把afterPropertiesSet改为destroy。

ApplicationContextAware的用法

　　其实我们看到—Aware就知道是干嘛用的了，就是属性注入的，但是这个ApplicationContextAware的不同地方在于，实现了这个接口的bean，当spring容器初始化的时候，会自动的将ApplicationContext注入进来：

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import org.apache.commons.lang.Validate;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.annotation.Lazy;
import org.springframework.stereotype.Service;
/**
 * applicationContext静态化
 * 使用了ApplicationContextAware接口的类，如果受spring容器管理的
 * 话，那么就会自动的调用ApplicationContextAware中的setApplicationContext方法
 * @author Hotusm
 *
 */
@Service
@Lazy(false)
public class SpringContextHolder implements ApplicationContextAware,DisposableBean{

    private static ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext)
            throws BeansException {

        SpringContextHolder.applicationContext=applicationContext;
    }
    //清空applicationContext 设置其为null
    @Override
    public void destroy() throws Exception {
        SpringContextHolder.clearHolder();
    }
    //获得applicationContext
    public static ApplicationContext getApplicationContext() {
        //assertContextInjected();
        return applicationContext;
    }

    public static void clearHolder(){
        applicationContext=null;
    }
    //获取Bean
    public static <T> T getBean(Class<T> requiredType){
        //assertContextInjected();
        return (T) getApplicationContext().getBean(requiredType);
    }
    @SuppressWarnings("unchecked")
    public static <T> T getBean(String name){
        assertContextInjected();
        return (T) getApplicationContext().getBean(name);
    }
    //判断application是否为空
    public static void assertContextInjected(){
        Validate.isTrue(applicationContext==null, "application未注入 ，请在springContext.xml中注入SpringHolder!");
    }

}

因为我们在做开发的时候，并不是说在每一个地方都能将属性注入到我们想要的地方去的，比如在Utils使用到dao，我们就不能直接注入了，这个时候就是我们需要封装springContext的时候了，而ApplicationContextAware就起了关键性的作用。

3：还有一种是注解的用法：

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。

几种Bean初始化及销毁时定义操作方式的执行顺序

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 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：

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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：

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<?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：

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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