使用Spring XML配置实现观察者模式？

Question

Suppose bean A is event publisher (observable) and beans B1 , B2 and B3 are event listeners (observers).

All Bs implement some BEvenListener interface.

How to code observable interface in A ? I wish to code something like usual Java's addEventListener(BEventListener listener) .

How to set all Bs to listen for A in Spring config? Usual "setter" allows only one injection, right? So, how to configure "adder" in Spring?

Spring provides ApplicationListener and ApplicationEventPublisherAware which allows to write beans which listen events, published onto context. But this mechanism works without configuration, ie XML file does not say which bean listen to which. Only types matter and all beans coded to listen some event will listen to it if present in context. Ie events are context-wide.

Is it possible to have directed event "channel" between publisher and listeners, configured in XML?

UPDATE

The only idea I got yet is to inject observable to filter events.

So, classes will be

public class Observable implements ApplicationEventPublisherAware {

public static class Event extends ApplicationEvent {

    public Event(Object source) {
        super(source);
    }

}

private ApplicationEventPublisher applicationEventPublisher;

@Override
public void setApplicationEventPublisher(ApplicationEventPublisher value) {
    this.applicationEventPublisher = value;
}

public void somecode() {
    applicationEventPublisher.publishEvent(new Event(this));
}

}

and

public class Observer implements ApplicationListener<Observable.Event> {

private Observable observable;

public void setObservable(Observable value) {
    this.observable = value;
}

@Override
public void onApplicationEvent(Event event) {
    if( event.getSource() == observable ) {
        // process event
    }
}

}

and the config will be

<bean id="observable" class="tests.observer.Observable"/>

<bean id="observer" class="tests.observer.Observer">
    <property name="observable" ref="observable"/>
</bean>

This will allow set publisher explicitly.

Answer 1

This is something I wish Spring would add to their XML configs, but as it stands you have to make use of the MethodInvokingFactoryBean if you want to avoid tying your code to Spring.

For the purposes of this example assume that the following method has been added your tests.observer.Observable class

void addObserver(Observer observer);

<bean id="observable" class="tests.observer.Observable"/>

<bean id="observer" class="tests.observer.Observer">
    <property name="observable" ref="observable"/>
</bean>

<bean id="addObserver" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
    <property name="targetObject" ref="observable" />
    <property name="targetMethod" value="addObserver"/>
    <property name="arguments">
       <list>
          <ref bean="observer" />
       </list>
    </property>
</bean>