Entities and the Java Persistence API

Now that you have explored how EJB provides business services through session beans, we’ll turn your attention to a different kind of component called entities, which are classes that represent tables in a database, and whose instances represent rows in those tables. Whereas session beans provide services to a client application, entities represent the business data. A common pattern is for a session bean to provide a convenient interface for manipulating entities in the context of transactional, security, access control, and other enterprise services. Methods to perform Create, Retrieve, Update, and Delete operations, also known as CRUD methods, are exposed on a session bean to the client to provide a “facade” pattern that we will use throughout the book.