Chapter 3: The Architecture of Enterprise JavaBeans

Overview

In chapter 2 we indicated that Enterprise JavaBeans (EJB) is a component of the Java-2 platform, Enterprise Edition (for details see [26]). In this model EJB takes over the part of the server-side application logic that is available in the form of components: the Enterprise Beans. This chapter introduces the architecture of Enterprise JavaBeans. Figure 3-1 shows Enterprise Beans (in their incarnations as entity, message-driven, and session beans) as the central elements.

Figure 3-1: Overview of the EJB architecture.

They contain the application logic used by the client programs. Enterprise Beans reside in an EJB container, which makes a run-time environment available to them (so that, for example, they can be addressed by client programs via the home and remote interfaces and have the possibility of communication among one another via the local home and local interfaces, so that life-cycle management can be provided). The EJB container is linked to services via the standard programming interface, services that are available to the bean (for example, access to databases via JDBC, access to a transaction service via JTA, and access to a message service via JMS). The EJB container is installed (possibly in addition to other containers) in an application server.

We shall now go into the details of the individual components of the architecture and their interrelationships.