After some posts about Outbound JCA connectors, let’s have a look at the concepts related to an Inbound JCA connector.
First question I always hear: “So, the server (legacy application) connects a client socket into a server socket on my J2EE server, right?” and I always answer: “depends”. People tends to think that the term inbound and outbound are related to TCP/IP connection, but, in fact, it is related to the flow of the process. In an outbound connector, our system is the actor and if you trace the flow of the call you’ll notice that it is leaving from our system to the legacy one; or perharps we could say outgoing. On the other hand, in an inbound connector, the actor is the legacy system that is triggering an ingoing message that is started outside our system and goes all the way into it.
Let’s see a sequence diagram of an inbound connector to make things clearer:
As you can see in the diagram, the component that ties the Application Server, the legacy system and the J2EE Application is the ActivationSpec.
Usually, instance configurations such as port, host and other instance related data is stored on the ActivationSpec, you may also have configuration in the ResourceAdapter itself, but remember that all the configurations placed on the ResourceAdapter will be shared across multiple ActivationSpecs that may be deployed on this ResourceAdapter.
The real class responsible for handling Enterprise Events is ResourceAdapter dependant and will be initialized during endpointActivation method call on a ResourceAdapter. These classes are usually implemented as a Thread or they implement the Work interface and are submitted to the container for execution through the WorkManager instance. If you opt to use a simple Thread, remember to daemonize it otherwise your application server wont be able to properly shutdown.
For the next weeks I’ll be posting some insights about how to implement an Inbound Connector using JCA.