Adam Bien's Weblog

ServiceFacade In Greater Detail - and Some EJB 3 Code

What is a ServiceFacade exactly? Yesterday we covered the difference between a ServiceFacade and a Service. ServiceFacade represents the boundary or an external component contract. Some aspects can be already derived from this fact:

  • It is the boundary between the (external) client and the realization of a component - so it is the only possible artifact with a remote interface.
  • ServiceFacade is stateless (only in exceptional cases stateful - why you would need state in procedures?)
  • Every method has to start a new transaction to be executed consistently
  • ServiceFacade is the single entry point into a component, so it can be easily decorated with aspects.

So in general case it is a:

  • @Stateless Session Bean
  • @Remote interface is optional, for web clients you should always use @Local interfaces
  • All methods are transactional - you will need @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW) - it is more explicit
  • From the conceptual point of view - a ServiceFacade should only coordinate Services and should not implement any business logic.  
  • A ServiceFacade should be deployed with a business interface - its easier to mock. No-interface view would work with frameworks like mockito - but is not worth the optimization.
  • If it is needed, you can implement cross-cutting aspects - if you are doing so, provide the interceptors on class and not the method level - is more consistent. I try to avoid the usage of @Interceptors - the less magic, the better. James Gosling said once: "(AOP) It's like giving them a chainsaw without any safety instructions." :-)



@Stateless
@Local(BookOrderingService.class)
@TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
@Interceptors(PreconditionInterceptor.class) //optional
public class BookOrderingServiceBean implements BookOrderingService {

   @EJB
   DeliveryService deliveryService;

}

The business interface is just a POJI. It is not dependent on the EJB API at all.

The code above (with several strategies, interceptors and ideas) was checked in (actually pushed :-)) into: http://kenai.com/projects/javaee-patterns


NEW workshop: Microservices with Java EE 7 and Java 8, January 26th, 2015, Airport Munich

A book about rethinking Java EE Patterns

Comments:

Hi Adam
Thank you for the posts.

I have a question about using the Service Facade pattern when you have to change some of the use cases per client.

BookOrderService for client one needs to send a email after the book was ordered and maybe trigger the supplier to get the book from overseas before delivery.

BookOrderService for client two need only to save the book and trigger the delivery service.

Would you use a strategy pattern or configure your EE environment to expose the specific boundary for the client that is using it?

Posted by Rentius on June 21, 2013 at 01:20 PM CEST #

Post a Comment:
  • HTML Syntax: NOT allowed
realworldpatterns.com
...the last 150 posts
...the last 10 comments
License