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ApplicationContextAware

时间:2014-01-14 21:43:17      阅读:593      评论:0      收藏:0      [点我收藏+]

1、实现了ApplicationContextAware接口,在Bean的实例化时会自动调用setApplicationContext()方法!

2、通过调用静态方法getBean即可获取

 

spring中提供一些Aware相关接口,像是BeanFactoryAware、 ApplicationContextAware、ResourceLoaderAware、ServletContextAware等等,实作这些 Aware接口的Bean在被初始之后,可以取得一些相对应的资源,例如实作BeanFactoryAware的Bean在初始后,Spring容器将会注入BeanFactory的实例,而实作ApplicationContextAware的Bean,在Bean被初始后,将会被注入 ApplicationContext的实例等等。
 Bean取得BeanFactory、ApplicationContextAware的实例目的是什么,一般的目的就是要取得一些档案资源的存取、相 关讯息资源或是那些被注入的实例所提供的机制,例如ApplicationContextAware提供了publishEvent()方法,可以支持基于Observer模式的事件传播机制。
 ApplicationContextAware接口的定义如下:

ApplicationContextAware.java

public interface ApplicationContextAware {

    void setApplicationContext(ApplicationContext context);

}


 我们这边示范如何透过实作ApplicationContextAware注入ApplicationContext来实现事件传播,首先我们的HelloBean如下:

HelloBean.java

package onlyfun.caterpillar;

 

import org.springframework.context.*;

 

public class HelloBean implements ApplicationContextAware {

    private ApplicationContext applicationContext;

    private String helloWord = "Hello!World!";

  

    public void setApplicationContext(ApplicationContext context) {

        this.applicationContext = context;

    }

  

    public void setHelloWord(String helloWord) {

        this.helloWord = helloWord;

    }

  

    public String getHelloWord() {

        applicationContext.publishEvent(

               new PropertyGettedEvent("[" + helloWord + "] is getted"));

        return helloWord;

    }

}


 ApplicationContext会由Spring容器注入,publishEvent()方法需要一个继承ApplicationEvent的对象,我们的PropertyGettedEvent继承了ApplicationEvent,如下:

PropertyGettedEvent.java

package onlyfun.caterpillar;

 

import org.springframework.context.*;

 

public class PropertyGettedEvent extends ApplicationEvent {

    public PropertyGettedEvent(Object source) {

        super(source);

    }

}


 当ApplicationContext执行publishEvent()后,会自动寻找实作ApplicationListener接口的对象并通知其发生对应事件,我们实作了PropertyGettedListener如下:

PrppertyGettedListener.java

package onlyfun.caterpillar;

 

import org.springframework.context.*;

 

public class PropertyGettedListener implements ApplicationListener {

    public void onApplicationEvent(ApplicationEvent event) {

        System.out.println(event.getSource().toString());  

    }

}


 Listener必须被实例化,这我们可以在Bean定义档中加以定义:

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

<!DOCTYPE beans PUBLIC "-//SPRING/DTD BEAN/EN" "http://www.springframework.org/dtd/spring-beans.dtd">

<beans>

    <bean id="propertyGetterListener" class="onlyfun.caterpillar.PropertyGettedListener"/>

 

    <bean id="helloBean" class="onlyfun.caterpillar.HelloBean">

        <property name="helloWord"><value>Hello!Justin!</value></property>

    </bean>

</beans>


 我们写一个测试程序来测测事件传播的运行:

Test.java

package onlyfun.caterpillar;

 

import org.springframework.context.*;

import org.springframework.context.support.*;

 

public class Test {

    public static void main(String[] args) {

        ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml");

      

        HelloBean hello = (HelloBean) context.getBean("helloBean");

        System.out.println(hello.getHelloWord());

    }

}


 执行结果会如下所示:

log4j:WARN No appenders could be found for logger

(org.springframework.beans.factory.xml.XmlBeanDefinitionReader).

log4j:WARN Please initialize the log4j system properly.

org.springframework.context.support.ClassPathXmlApplicationContext:

displayName=[org.springframework.context.support.ClassPathXmlApplicationContext;

hashCode=33219526]; startup date=[Fri Oct 29 10:56:35 CST 2004];

root of ApplicationContext hierarchy

[Hello!Justin!] is getted

Hello!Justin!


 以上是以实作事件传播来看看实作Aware接口取得对应对象后,可以进行的动作,同样的,您也可以实作ResourceLoaderAware接口:

ResourceLoaderAware.java

public interface ResourceLoaderAware {

    void setResourceLoader(ResourceLoader loader);

}


 实作ResourceLoader的Bean就可以取得ResourceLoader的实例,如此就可以使用它的getResource()方法,这对于必须存取档案资源的Bean相当有用。
 基本上,Spring虽然提供了这些Aware相关接口,然而Bean上若实现了这些界面,就算是与Spring发生了依赖,从另一个角度来看,虽然您可以直接在Bean上实现这些接口,但您也可以透过setter来完成依赖注入,例如:

HelloBean.java

package onlyfun.caterpillar;

 

import org.springframework.context.*;

 

public class HelloBean {

    private ApplicationContext applicationContext;

    private String helloWord = "Hello!World!";

  

    public void setApplicationContext(ApplicationContext context) {

        this.applicationContext = context;

    }

  

    public void setHelloWord(String helloWord) {

        this.helloWord = helloWord;

    }

  

    public String getHelloWord() {

        applicationContext.publishEvent(new PropertyGettedEvent("[" + helloWord + "] is getted"));

        return helloWord;

    }

}


 注意这次我们并没有实作ApplicationContextAware,我们在程序中可以自行注入ApplicationContext实例:

ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml");

      

HelloBean hello = (HelloBean) context.getBean("helloBean");

hello.setApplicationContext(context);

System.out.println(hello.getHelloWord());


 就Bean而言,降低了对Spring的依赖,可以比较容易从现有的框架中脱离

ApplicationContextAware

原文:http://www.cnblogs.com/Dhouse/p/3513705.html

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