Enterprise JavaBeans, Second Edition

Chapter 6. Entity Beans

In Chapter 4, we started developing some simple enterprise beans, skipping over a lot of the details in the process. In this chapter, we’ll take a thorough look at the process of developing entity beans. On the surface, some of this material may look familiar, but it is much more detailed and specific to entity beans.

Entity beans model business concepts that can be expressed as nouns. This is a rule of thumb rather than a requirement, but it helps in determining when a business concept is a candidate for implementation as an entity bean. In grammar school you learned that nouns are words that describe a person, place, or thing. The concepts of “person” and “place” are fairly obvious: a person bean might represent a customer or a passenger, and a place bean might represent a city or a port-of-call. Similarly, entity beans often represent “things”: real-world objects like ships, cabins, and so on. A bean can even represent a fairly abstract “thing,” such as a ticket or a reservation. Entity beans describe both the state and behavior of real-world objects and allow developers to encapsulate the data and business rules associated with specific concepts; a cabin bean encapsulates the data and business rules associated with a cabin, and so on. This makes it possible for data associated with a concept to be manipulated consistently and safely.

In Titan’s cruise ship business, we can identify hundreds of business concepts that are nouns and therefore could conceivably ...