Example 1: Centralizing Exchange Rates

Abstract

In the J2EE programming paradigm, Enterprise JavaBeans are the glue that binds the server front end with its back end. The “front end” of a server is the part that receives all commands from the user and, after all processing of a command is done, and sends the results back to the user. The “back end” of a server is the part where all data is collected to business and aggregate objects, according to the instructions of the user for the particular task. The back end also hides various complexities that are associated with moving data to and from legacy data sources. Chapters 9 through 11 demonstrate three different scenarios where EJBs are used:

• Chapter 9: Direct Java application interaction with the EJB tier using a stateless session ETB server

• Chapter 10: Migrating a Web application from old-style servlet-to-database interaction to session EJB proxy operation.

• Chapter 11: Continue migration to include aggregate value objects and back-end tier abstraction using Entity EJBs.