栏目:Web开发 作者:admin 日期:2015-04-29 评论:0 点击: 4,116 次
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的目的是什么,一般的目的就是要取得一些资源的存取、或是使用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:
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ApplicationContextAware.java public interface ApplicationContextAware { void setApplicationContext(ApplicationContext context); } |
下面说明一下如何通过实现ApplicationContextAware注入ApplicationContext来实现事件传播,首先编写HelloBean如下:
HelloBean.java
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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:
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PropertyGettedEvent.java 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
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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:
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<?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="PropertyGettedListener"/> <bean id="helloBean" class="HelloBean"> <property name="helloWord"><value>Hello Swiftlet!</value></property> </bean> </beans> |
我们写一个测试程序来测测事件传播的运行:
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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:
[Hello Swiftlet!] is getted
Hello Swiftlet!
以上是以实现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,你也可以实作ResourceLoaderAware接口:
ResourceLoaderAware.java
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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上若实现了这些接口,就算是与Spring发生了依赖,从另一个角度来看,虽然你以直接在Bean上实现这些接口,但也可以透过setter来完成依赖注入,例如:
HelloBean.java
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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。
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