全部博文(695)
分类: Java
2017-06-27 09:51:39
转自: http://www.blogjava.net/syniii/archive/2010/11/24/338906.html
Spring中提供一些Aware相关接口,像是BeanFactoryAware、
ApplicationContextAware、ResourceLoaderAware、ServletContextAware等等,实现这些
Aware接口的Bean在被初始之后,可以取得一些相对应的资源,例如实现BeanFactoryAware的Bean在初始后,Spring容器将会注入BeanFactory的实例,而实现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现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,会自动寻找实现ApplicationListener接口的对象并通知其发生对应事件,我们实现了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:
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!
以上是以实现事件传播来看看实现Aware接口取得对应对象后,可以进行的动作,同样的,您也可以实现ResourceLoaderAware接口:
ResourceLoaderAware.java
public interface ResourceLoaderAware {
void setResourceLoader(ResourceLoader loader);
}
实现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现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。