Enterprise JavaBeans, Fourth Edition

Developing a Session Bean

Session beans act as agents to the client, controlling taskflow (the business process) and filling the gaps between the representation of data by entity beans and the business logic. Session beans are often used to manage interactions between entity beans and can perform complex manipulations of beans. Since we have defined only one entity bean so far, we will start by manipulating this bean. The interactions of entity beans within session beans is explored in greater detail in Chapter 11.

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 change over time—hence the importance of separating the data itself from the taskflow. 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. The definition of an entity bean should only be changed within the context of a larger process—for example, a major redesign of the business system.

We’ll start developing a TravelAgent EJB that is responsible for the taskflow of booking a passage on a cruise. This session bean will be used in client applications accessed by travel ...