Written in the Java programming language, an enterprise bean is a server-side component that encapsulates the business logic of an application. The business logic is the code that fulfills the purpose of the application. In an inventory control application, for example, the enterprise beans might implement the business logic in methods called checkInventoryLevel and orderProduct. By invoking these methods, clients can access the inventory services provided by the application.
Benefits of Enterprise Beans
For several reasons, enterprise beans simplify the development of large, distributed applications. First, because the EJB container provides system-level services to enterprise beans, the bean developer can concentrate on solving business problems. The EJB containerand not the bean developeris responsible for system-level services such as transaction management and security authorization.
Second, because the beansand not the clientscontain the application's business logic, the client developer can focus on the presentation of the client. The client developer does not have to code the routines that implement business rules or access databases. As a result, the clients are thinner, a benefit that is particularly important for clients that run on small devices.
Third, because enterprise beans are portable components, the application assembler can build new applications from existing beans. These applications can run on any compliant Java EE server provided that they use the standard APIs.
When to Use Enterprise Beans
You should consider using enterprise beans if your application has any of the following requirements:
Types of Enterprise Beans
Table 201 summarizes the two types of enterprise beans. The following sections discuss each type in more detail.
Entity beans have been replaced by Java Persistence API entities. For information about entities, see Chapter 24, Introduction to the Java Persistence API.