53.2.1 Using the Inbound Resource Adapter

In most cases, Java EE application developers use inbound resource adapters developed by a third party. To use an inbound resource adapter, a Java EE application includes a message-driven bean with the following characteristics.

• The MDB implements the business interface defined by the resource adapter.

• The MDB specifies configuration parameters to activate the resource adapter.

The business interface defined by the resource adapter is not specified in the Java EE Connector Architecture; it is specific to the EIS.

The MDB in this example is defined as follows:

@MessageDriven(
    activationConfig = {
      @ActivationConfigProperty(propertyName = "port", 
                                propertyValue = "4008")
    }
)
public class TrafficMdb implements TrafficListener { ... }

The TrafficListener interface is defined in the API package of the resource adapter. The resource adapter requires the MDB to provide the port property.

When the MDB is deployed, it activates the traffic-rar resource adapter, which invokes the methods of the MDB to process traffic information updates. Then the MDB filters the updates for a particular city and publishes the results to a JMS topic.

In this particular example, the TrafficListener interface is empty. In addition to this interface, the resource adapter provides the TrafficCommand annotation and uses reflection to discover which methods in the MDB are decorated with this annotation:

@MessageDriven(...)
public class TrafficMdb implements TrafficListener {

    @TrafficCommand(name="report", info="Process report")
    public void processReport(String jsonReport) { ... }
    ...
}

This approach enables you to adapt the MDB to support new features in the EIS without having to modify the TrafficListener interface or the resource adapter module.

53.2.2 Implementing the Inbound Resource Adapter

The traffic-rar module implements the inbound resource adapter contract from the Java EE Connector Architecture for the simple traffic information system (EIS) used in this example. The architecture of the inbound resource adapter is shown in Figure 53-4.

Figure 53-4 Architecture of the traffic Example

Description of "Figure 53-4 Architecture of the traffic Example"

The traffic-rar module implements the interfaces listed in Table 53-3.

When an MDB activates the inbound resource adapter, the container invokes the endpointActivation method in the TrafficResourceAdapter class:

@Connector(...)
public class TrafficResourceAdapter implements ResourceAdapter, Serializable {
    ...
    @Override
    public void endpointActivation(MessageEndpointFactory endpointFactory, 
                                   ActivationSpec spec) 
                                   throws ResourceException {
        Class endpointClass = endpointFactory.getEndpointClass();
        /* this method is called from a new thread in the example: 
        MessageEndpoint endpoint = endpointFactory.createEndpoint(null); */
    }
}

The getEndpointClass method returns the Class type of the MDB performing the activation, which enables the resource adapter to use reflection to find methods annotated with @TrafficCommand in the MDB.

The createEndpoint method returns an instance of the MDB. The resource adapter uses this instance to invoke the methods of the MDB when it receives requests from the EIS.

After obtaining the message endpoint instance (MDB), the resource adapter uses the work management contract to create the traffic service subscriber thread that receives traffic updates from the EIS. The resource adapter obtains the WorkManager instance from the bootstrap context as follows:

WorkManager workManager;
...
@Override
public void start(BootstrapContext ctx) ... {
    workManager = ctx.getWorkManager();
}

The resource adapter schedules the traffic service subscriber thread using the work manager:

tSubscriber = new TrafficServiceSubscriber(tSpec, endpoint);
workManager.scheduleWork(tSubscriber);

The TrafficServiceSubscriber class implements the javax.resource.spi.Work interface from the work management contract.

The traffic service subscriber thread uses reflection to invoke the methods in the MDB:

private String callMdb(MessageEndpoint mdb, Method command, 
                       String... params) ... {
    String resp;
    /* this code contains proper exception handling in the sources */
    mdb.beforeDelivery(command);
    Object ret = command.invoke(mdb, (Object[]) params);
    resp = (String) ret;
    mdb.afterDelivery();
    return resp;
}

For more details, see the code and the comments in the traffic-rar module.

53.2.3 Running the traffic Example

You can use either NetBeans IDE or Maven to build, package, deploy, and run the traffic example.