Enterprise JavaBeans, Third Edition

Developing a Session Bean

Session beans act as agents to the client, controlling workflow (the business process) and filling the gaps between the representation of data by entity beans and the business logic that interacts with that data. Session beans are often used to manage interactions between entity beans and can perform complex manipulations of beans to accomplish certain tasks. Since we have defined only one entity bean so far, we will focus on a complex manipulation of the Cabin EJB rather than the interactions of the Cabin EJB with other entity beans. The interactions of entity beans within session beans will be explored in greater detail in Chapter 12.

Client applications and other beans use the Cabin EJB in a variety of ways. Some of these uses were predictable when the Cabin EJB was defined, but many were not. After all, an entity bean represents data—in this case, data describing a cabin. The uses to which we put that data will change over time—hence the importance of separating the data itself from the workflow. In Titan’s business system, for example, we may need to list and report on cabins in ways that were not predictable when the Cabin EJB was defined. Rather than change the Cabin EJB every time we need to look at it differently, we will obtain the information we need using a session bean. Changing the definition of an entity bean should be done only within the context of a larger process—for example, a major redesign of the business system.

In Chapter 1 and ...