J2EE application servers incorporate a standard framework for integrating Enterprise Information Servers with applications, called the J2EE Connection Architecture (JCA). JBoss ESB provides two gateways which integrate with this technology, the JMS/JCA gateway, and the generic JCA gateway.
The JCA framework supports a mechanism which allows a resource adapter to push messages concurrently to a registered listener, a process called message inflow in JCA terminology, with the type of message being specific to the Resource Adapter and its purpose.
The most common message type is JMS and, for that reason, JBoss ESB provides a specialized gateway to handle this use case. This gateway supports the configuration of the standard JMS gateway while allowing the JCA resource adapter specific configuration to be included.
Enabling the JMS/JCA gateway is simply a matter of modifying the configuration of the JMS gateway and changing the provider name from <jms-provider> to <jms-jca-provider>. The JMS/JCA gateway will then, by default, create an activation specification for the jms-ra JCA provider, although alternative JCA providers can also be used by specifying the name of their Resource Adapter deployment in the adapter attribute.
The jms_transacted quickstart demonstrates how to use the JMS/JCA provider as both a gateway and a listener for an ESB service. Run through the example and compare the configuration with that of the JMS provider, paying particular attention to the <activation-config> element which allows the ESB to specify properties to be applied directly to the activation specification of the JCA provider.
JBoss ESB also provides a gateway for processing message inflow from generic JCA resource adapters, allowing the ESB to handle any message types supported by the associated adapter. One example of this capability would be the processing of e-mails, where an Email Resource Adapter would push the message contents into the ESB through the JCA gateway.
Any discussion of this adapter is beyond the scope of this book as its configuration is tied very closely to the JCA Resource Adapter being used to inflow the messages. It is, however, important that its existence be known so that it can be explored should such a requirement arise.