Download free ebook : Sun--The_J2EE_1.4_Tutorial.pdf
Guide to developing enterprise applications for the Java 2 Platform, Enterprise Edition (J2EE) version 1.4.

Not only can you deliver innovative business solutions to market faster than ever, but also your platform-independent J2EE component-based solutions are not tied to the products and application programming interfaces (APIs) of any one vendor. Vendors and customers enjoy the freedom to choose the products and components that best meet their business and technological requirements.

This tutorial uses examples to describe the features and functionalities available in the J2EE platform version 1.4 for developing enterprise applications. Whether you are a new or an experienced developer, you should find the examples and accompanying text a valuable and accessible knowledge base for creating your own solutions.

If you are new to J2EE enterprise application development, this chapter is a good place to start. Here you will review development basics, learn about the J2EE architecture and APIs, become acquainted with important terms and concepts, and find out how to approach J2EE application programming, assembly, and deployment.

Distributed Multitiered Applications

The J2EE platform uses a distributed multitiered application model for enterprise applications. Application logic is divided into components according to function, and the various application components that make up a J2EE application are installed on different machines depending on the tier in the multitiered J2EE environment to which the application component belongs. Figure 1–1 shows two multitiered J2EE applications divided into the tiers described in the following list. The J2EE application parts shown in Figure 1–1 are presented in J2EE Components (page 3).

• Client-tier components run on the client machine.
• Web-tier components run on the J2EE server.
• Business-tier components run on the J2EE server.
• Enterprise information system (EIS)-tier software runs on the EIS server.

Although a J2EE application can consist of the three or four tiers shown in Figure 1–1, J2EE multitiered applications are generally considered to be threetiered applications because they are distributed over three locations: client machines, the J2EE server machine, and the database or legacy machines at the back end. Three-tiered applications that run in this way extend the standard twotiered client and server model by placing a multithreaded application server between the client application and back-end storage.