Revisiting the J2EE Platform

You learned a lot about enterprise computing yesterday. You learned specifically about how business needs force the evolution of application architectures; today, most applications are distributed across multiple machines. This approach, the n-tier model, gives rise to different ways of writing and structuring applications. Units of functionality— components—provide modularity that allow multiple developers to work more easily on different parts of the application. Use of a component framework also allows developers to apply third-party components to speed development. These loosely-coupled components may run as an application on a desktop client, within a Web server, or even on a server that connects to a legacy system. In addition, data has undergone a revolution. Data sources now go beyond simple, relational databases containing tables to encompass databases that contain serialized objects or plain text files containing XML. Alternatively, data may take the form of user information in an LDAP directory or information in an Enterprise Resource Planning (ERP) system.

Applications written in traditional programming languages that do not have supporting frameworks simply cannot perform the operations required by today's environment. Instead, you must employ component-aware programming languages together with frameworks dedicated to enterprise computing. As you have already seen, J2EE is such a framework. Although the environment within which J2EE operates might sound daunting, J2EE isn't. When you write J2EE applications, you still write Java code, and you still get to use the J2SE classes with which you are familiar.

To successfully use J2EE, you must

• Install and configure your J2EE environment

• Understand J2EE roles

• Appreciate the purpose of containers

• Understand how you can use J2EE components

• Understand the services that containers supply to components

• Learn or explore a new set of APIs

Yesterday's lesson introduced the first four points in the list. You will explore them in more depth today. After you understand these, you will be ready for tomorrow, when you will start to apply the new APIs and to code real applications against them.