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Chapter 2 An introduction to EJB development The Enterprise JavaBeans (EJB) specification formally defines a Java server-side component model and a programming interface for application servers. Developers build the components, called enterprise beans, to contain the business logic of the enterprise. Enterprise beans run on an EJB server that provides services such as transaction management and security to the beans. Developers don t have to worry about programming these low-level and complex services, but can focus on encapsulating the business rules of an organization or system within the beans, knowing that the services are available to the beans when they are needed. While the Enterprise JavaBeans specification is the ultimate authority on the EJB framework, it s primarily useful to vendors such as Borland who build the EJB servers and containers the beans run in. This book will help you, the JBuilder developer, learn what you want to know about developing enterprise beans with JBuilder. Why we need Enterprise JavaBeans The client-server model of application development has enjoyed considerable popularity. The client application resides on a local machine and accesses the data in a data store such as a relational database management system. This model works well as long as the system has only a few users. As more and more users need access to the data, these applications don t scale well to meet the demands. Because the client contains the logic, it must be installed on each machine. Management becomes increasingly difficult. Gradually the benefits of dividing applications into more than the two tiers of the client- server model become apparent. In a multi-tier application, only the user interface stays on local machines while the logic of the application runs in the middle tier on a server. The final tier is still the stored data. When the logic of an application needs updating, changes are made to the software of the middle tier on the server, greatly simplifying the management of updates. But creating reliable, secure, and easily managed distributed applications is notoriously difficult. For example, managing transactions over a distributed system is a major task. Chapter 2: An introduction to EJB development 5
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