What Is an Enterprise Bean?

Benefits of Enterprise Beans

When to Use Enterprise Beans

Types of Enterprise Beans

What Is an Enterprise Bean?

Written in the Java programming language, anenterprise bean is a server-side componentthat encapsulates the business logic of an application. The business logic is thecode that fulfills the purpose of the application. In an inventory control application,for example, the enterprise beans might implement the business logic in methods calledcheckInventoryLevel andorderProduct. By invoking these methods, clients can access the inventory servicesprovided 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 developercan concentrate on solving business problems. The EJB container, rather than the beandeveloper, is responsible for system-level services such as transaction management and security authorization.

Second, because the beans rather than the clients contain the application’s business logic, theclient developer can focus on the presentation of the client. The client developerdoes not have to code the routines that implement business rules or accessdatabases. As a result, the clients are thinner, a benefit that is particularlyimportant for clients that run on small devices.

Third, because enterprise beans are portable components, the application assembler can build newapplications from existing beans. These applications can run on any compliant Java EEserver provided that they use the standard APIs.

When to Use Enterprise Beans

You should consider using enterprise beans if your application has any of thefollowing requirements:

• The application must be scalable. To accommodate a growing number of users, you may need to distribute an application’s components across multiple machines. Not only can the enterprise beans of an application run on different machines, but also their location will remain transparent to the clients.

• Transactions must ensure data integrity. Enterprise beans support transactions, the mechanisms that manage the concurrent access of shared objects.

• The application will have a variety of clients. With only a few lines of code, remote clients can easily locate enterprise beans. These clients can be thin, various, and numerous.

Types of Enterprise Beans

Table 20-1 summarizes the two types of enterprise beans. The following sections discuss eachtype in more detail.

Table 20-1 Enterprise Bean Types

Note -Entity beans have been replaced by Java Persistence API entities. For information aboutentities, seeChapter 24, Introduction to the Java Persistence API.

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