124 Chapter 6 customer information, and (Web site) more. An
124 Chapter 6 customer information, and more. An entity bean does not perform complex tasks or workflow logic, such as billing a customer. Rather, an entity bean is the customer itself. Entity beans represent persistent state objects (things that don t go away when the user goes away). For example, you might want to read a bank account data into an entity bean instance, thus loading the stored database information into the in-memory entity bean instance s fields. You can then play with the Java object and modify its representation in memory because you re working with convenient Java objects, rather than bunches of database records. You can increase the bank account balance in-memory, thus updating the entity bean s in-memory bank account balance field. Then you can save the Java object, pushing the data back into the underlying store. This would effectively deposit money into the bank account. The term entity bean is not always used stringently. Sometimes it refers to an in-memory Java object instance of an entity bean class, and sometimes it refers to database data that an in-memory Java object instance represents. To make the distinction clear, we will use the following two terms: The entity bean instance is the in-memory view into the database. It is an instance of your entity bean class. The entity bean data (or data instance) is the physical set of data, such as a bank account record, stored in the database. In summary, you should think of an entity bean instance as the following: An in-memory Java representation of persistent data that knows how to read itself from storage and populate its fields with the stored data An object that can then be modified in-memory to change the values of data Persistable, so that it can be saved back into storage again, thus updating the database data About the Files That Make Up an Entity Bean An entity bean contains the standard set of files that all EJB components have, including the remote and/or local interface, the home and/or local home interface, the enterprise bean class, and the deployment descriptor. There are several noteworthy differences between entity bean files and other types of EJB components. The entity bean class maps to an entity definition in a database schema. For example, an entity bean class could map to a relational
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