The business tier is where developers create their business logic
The only type of software component deployable at the business tier are EJBs. EJBs are specially
Message Driven Beans
Of the different types of EJBs, session beans are further divided into stateless session beans and stateful session beans. The
exist only in context of a
Entity beans are associated with data stored in a database (typically relational), while Message Driven Beans ( MDBs ) are called when incoming messages are received by at a specific Java Message Service (JMS) destination.
Figure 4-3 shows the EJBs that can be deployed at the business tier.
Figure 4-3: EJBs deployable at Geronimo’s business tier
All of these classifications are more important to application developers than to administrators/
Most EJBs are prebundled as a module for deployment. Geronimo administrators and deployers work with a bundled archive rather than individual EJBs.
An important thing to realize from Figure 4-3 is that entity beans may require the configuration of a Java Database Connectivity (JDBC) data source for storing the
EJBs to be deployed to the Geronimo server must be bundled in an EJB JAR file. According to the J2EE 1.4 specifications, the EJBs must be bundled together with a standard deployment descriptor called ejb-jar.xml , placed in the META-INF directory of the archive.
An EAR file can contain one or more WAR files containing servlets and JSPs, and one or more JAR files containing EJBs (as well as other resource adapter JARs). It must include a standard deployment descriptor, called application.xml , in the META-INF directory. This deployment descriptor should reference the modules that are a part of the overall enterprise application.
The EJB container inside Geronimo is a special version of the
version 2.1 container.
The OpenEJB container integration within Geronimo features the following:
Support of EJB 2 Container Managed Persistence 2
Support of EJB QL
Support of EJB 2.1 Web services
Chapter 12 will provide detailed information on the configuration and deployment of EJBs (either alone in an EJB JAR or as a part of an EAR) to the OpenEJB container.
To provide support for MDBs and general message queues (MQ) services for software components, Geronimo uses
is a very popular Open Source message queues broker implementation.
provides a JCA 1.5–compatible resource adapter, which is integrated into Geronimo. This allows application developer to use the
ActiveMQ supports MDBs by accepting inbound connections. This means that messages sent to a message destination (such as a JMS topic or queue) can be used to trigger a call to an MDB. This support is leveraged by Geronimo in its MDB implementation.
Chapter 16 provides more details on configuration of ActiveMQ at the business tier.