Revisiting the J2EE Platform

You learned a lot about enterprise computing yesterday. Specifically you learned about how business needs force the evolution of application architectures; today, most applications are distributed across multiple machines. This n-tier model gives rise to different ways of writing and structuring applications. Units of functionality, or components, provide modularity that allow multiple developers to work on different parts of the application.

Use of a component framework 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 (Lightweight Directory Access Protocol) naming directory or information in an Enterprise Resource Planning (ERP) system.

J2EE is a framework that supports the requirements of applications developed to support enterprise wide functionality. Although the environment within which J2EE operates might sound daunting, J2EE itself 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 gave an introduction to the first four points in the list. You will explore these in more depth today. After you understand these, you will be ready for tomorrow, when you will start to apply the new APIs and code real applications against them. At the end of today's work you will install Sun Microsystems' J2EE SDK and configure a database for use with the examples and exercises presented in the rest of this book.