Question

I’m writing an inbound resource adapter (connector module) on Glassfish 3.1 and I’ve noticed in the Java EE SDK samples that an MDB is used to deliver messages from an EIS to Glassfish applications. Is it necessary to use an MDB if the target object is an EJB? Would it be wise to do a JNDI lookup for the target EJB and deliver to it directly, avoiding the MDB altogether?

Thanks!

Answer 1

In the latter case you perform a synchronous operation, whereas the first approach is an asynchronous one. In application to application (A2A) integration scenarios it’s almost always a good decision to implement an asynchronous interface. A lot has been written about this, let me just refer to the Java documentation itself, e.g. section 6.3.3:

When designing your application, you need to decide whether to use
synchronous or asynchronous integration with its target EISes and
existing applications. Both synchronous and asynchronous integration
approaches are valid for application integration, and the choice
should be based on the integration requirements and use cases. Base
your decision on the following guidelines.

• Quality of services required–The use of a queue or a publish-subscribe system provides higher quality of services, such as
  message routing and reliable message delivery, than synchronous
  communications.
• Application throughput–Asynchronous messaging can lead to better throughput because a queue buffers messages, supports message routing,
  and guarantees message delivery.
• Transactional integration–A synchronous communication model is more suitable when an application needs to perform secure and
  transactional access to one or more EISes synchronously for client
  request processing. In such cases an application can afford the
  overhead of tighter coupling with an EIS to ensure higher quality
  request processing and error handling.
• Programming model complexity–An asynchronous communication programming model is more complex than the more common synchronous
  request-response model. While the asynchronous model provides more
  services, the cost is greater application complexity and more work on
  the part of developers.

To conclude, maybe it’s not necessary, but it may be wise to implement an MDB.