Spring中提供一些Aware相關(guān)接口，像是BeanFactoryAware、 ApplicationContextAware、ResourceLoaderAware、ServletContextAware等等，實(shí)現(xiàn)這些 Aware接口的Bean在被初始之后，可以取得一些相對(duì)應(yīng)的資源，例如實(shí)現(xiàn)BeanFactoryAware的Bean在初始后，Spring容器將會(huì)注入BeanFactory的實(shí)例，而實(shí)現(xiàn)ApplicationContextAware的Bean，在Bean被初始后，將會(huì)被注入 ApplicationContext的實(shí)例等等。
Bean取得BeanFactory、ApplicationContextAware的實(shí)例目的是什么，一般的目的就是要取得一些檔案資源的存取、相 關(guān)訊息資源或是那些被注入的實(shí)例所提供的機(jī)制，例如ApplicationContextAware提供了publishEvent()方法，可以支持基于Observer模式的事件傳播機(jī)制。
ApplicationContextAware接口的定義如下：
ApplicationContextAware.java
public interface ApplicationContextAware {
void setApplicationContext(ApplicationContext context);
}
我們這邊示范如何透過(guò)實(shí)現(xiàn)ApplicationContextAware注入ApplicationContext來(lái)實(shí)現(xiàn)事件傳播，首先我們的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會(huì)由Spring容器注入，publishEvent()方法需要一個(gè)繼承ApplicationEvent的對(duì)象，我們的PropertyGettedEvent繼承了ApplicationEvent，如下：
PropertyGettedEvent.java
package onlyfun.caterpillar;
import org.springframework.context.*;
public class PropertyGettedEvent extends ApplicationEvent {
public PropertyGettedEvent(Object source) {
super(source);
}
}
當(dāng)ApplicationContext執(zhí)行publishEvent()后，會(huì)自動(dòng)尋找實(shí)現(xiàn)ApplicationListener接口的對(duì)象并通知其發(fā)生對(duì)應(yīng)事件，我們實(shí)現(xiàn)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必須被實(shí)例化，這我們可以在Bean定義檔中加以定義：
<?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>
我們寫(xiě)一個(gè)測(cè)試程序來(lái)測(cè)測(cè)事件傳播的運(yùn)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());
}
}
執(zhí)行結(jié)果會(huì)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!
以上是以實(shí)現(xiàn)事件傳播來(lái)看看實(shí)現(xiàn)Aware接口取得對(duì)應(yīng)對(duì)象后，可以進(jìn)行的動(dòng)作，同樣的，您也可以實(shí)現(xiàn)ResourceLoaderAware接口：
ResourceLoaderAware.java
public interface ResourceLoaderAware {
void setResourceLoader(ResourceLoader loader);
}
實(shí)現(xiàn)ResourceLoader的Bean就可以取得ResourceLoader的實(shí)例，如此就可以使用它的getResource()方法，這對(duì)于必須存取檔案資源的Bean相當(dāng)有用。
基本上，Spring雖然提供了這些Aware相關(guān)接口，然而B(niǎo)ean上若實(shí)現(xiàn)了這些界面，就算是與Spring發(fā)生了依賴，從另一個(gè)角度來(lái)看，雖然您可以直接在Bean上實(shí)現(xiàn)這些接口，但您也可以透過(guò)setter來(lái)完成依賴注入，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;
}
}
注意這次我們并沒(méi)有實(shí)現(xiàn)ApplicationContextAware，我們?cè)诔绦蛑锌梢宰孕凶⑷階pplicationContext實(shí)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，降低了對(duì)Spring的依賴，可以比較容易從現(xiàn)有的框架中脫離。