Is there a spring equivalent to the EJB Observer Pattern?

[garpinc2]

I basically would like that a service method fire events related to what was inserted, updated or deleted in the DAO layer and any other arbritrary events I might fire explicitly in my service layer. These events should somehow be available in my caller. So the code would be like

Caller:

serviceInstance.addListener(eventListener);
serviceInstance.doSomething();
if (eventListener.isEvent1Fired()) {
...
}

} finally {
serviceInstance.removeListener(eventListener);
}


ServiceInstance:
void doSomeThing() {
fireEvent1();
}


Haven't specified in full the interface. But hopefully one of you will get the idea and let me know if there is a similar thing is Spring that is available for doing this sort of thing.

Thanks,
Garry

EJB Observer Pattern
This article explains how to implement the observer pattern in a suite of integrated EJB apps. The suite has a shared repository and each EJB application has it own repository. Every application in the suite runs on a separate host. Each application needs to observe changes in the shared repository as they occur -- and within the transaction in which they occur. If a proposed change to the shared data is unacceptable to any given application then the transaction must be aborted before the change is made permanent.

[Rod Johnson]

You should be able to use a combination of Spring AOP (to capture and fire events without code duplication) and the event publication method oof a Spring ApplicationContext to do this. See EventPublicationInterceptor as a starting point.

Without a URL, it's hard to comment on the article. It sounds like it's not EJB specific. If you need to propagate events around a cluster, you should look at JMS. You could have a listener that fires Spring application context events to a JMS queue.

[garpinc2]

I looked for an example but I can't find any. Could you provide an example of how best to accomplish this in a Spring way?

Basically what I want to accomplish is the best pattern for the following:

1) Struts Action-> calls Spring Transaction Proxied Service Method
2) need feedback in struts action about events (successes and errors) that occured in Service Method. Also the service could have derived a value or multiple values which need to be passed back to the client in request attributes.

For instance

struts action:
service method:
Listener quantityNotificationListener = new QuantityNotificationListener();
getWebApplicationContext()
.registerNotificationListener(quantityNotification Listener);
Listener eventListener = new EventListener
getWebApplicationContext()
.registerEventListener(eventListener);

processOrder(orderId,orderName,orderQuantity);
// now some through WebApplicationContext
// action is aware of fired events and fired notifications i.e:
request.setAttribute("NEW_QUANTITY", quantityNotificationListener.getNotificationObject ());
addMessages to ActionMessages based on events fired

service method:
processOrder(orderId,orderQuantity) {
try {
Order order = getOrderFromSupply(orderId,orderQuantity);
} catch (OrderNotAvailableException e) {
fireEvent(new OrderNotAvailableEvent());
try {
savebackOrder(orderId,orderQuantity);
} catch (OrderDiscontinuedException e) {
fireEvent(new OrderDiscontinuedEvent());
}
completeOrder(order);
fireNotify(new QuantityNotification());
fireEvent(new OrderCompletedEvent());
}



}

[garpinc2]

I think the following is a pretty good article to illustrate the programming issues I'm trying to address.

http://www.javaworld.com/javaworld/j...avatip110.html