Sams Teach Yourself BEA WebLogic Server 7.0 in 21 Days

Up to this point you have covered Java servlets, JavaServer Pages, and Java Database Connectivity technologies supported by WebLogic Server 7.0. Over the next few days, you will spend time exploring the next set of enterprise technologies that are a part of the J2EE specification: the Enterprise JavaBean (EJB) component model.

The primary goal of the EJB component model is to define a standard and consistent way for server-side application components to be written and deployed on all application servers that support the EJB specification. In essence, EJB brings the same Write Once Run Anywhere concept of standard Java to server-side components. Later today, you will see how the EJB specification forces vendors of the EJB containers in application servers like WebLogic Server to adhere to the EJB design contracts. You already covered the concepts of various technologies that are part of J2EE and the EJB component model during Day 2, "Understanding J2EE Concepts."

Before you proceed you need to understand what an EJB is. An EJB is a Java class residing on the server side and implements the business logic for multitier enterprise applications. The EJB specification aims to standardize the development of these server-side Java classes. As a result, the EJB specification has clearly demarcated the middle-tier of the three-tier architecture from a combined business logic layer into two parts: the transactional business logic layer and the data logic layer. For each of these layers, the EJB specification defines standard component models to develop transactional business logic components and data logic components.

The EJB specification defines that transactional business logic can be built using session beans. For the data logic, the EJB specification defines entity beans. A third type of component model that the EJB specification defines is message beans. You will be studying data logic capable entity beans and messaging-capable message beans in the coming days. Today and tomorrow you will be focusing on learning about the two types of session beans stateful session beans and stateless session beans.