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Take a Tour of Web Tier Technologies
Use the latest J2EE 1.4 Web tier technologies to your advantage.
by Paul Philion

JavaOne, June 28, 2004

The Web tier has existed in Web-based applications since the introduction of the thin client. The move from the fat-client, two-tier enterprise application models (traditional client/server architecture) to Web-browser-based, thin-client n-tier application models required the introduction of a tier to handle the Web-based presentation logic distinct from the business logic in the middle tier.

The earliest Web tier implementations relied on dynamic HTML generation using server-side scripting languages such as Perl. Those prototypical applications were plagued with problems: They were inefficient (some required a new process per HTTP request); they didn't scale at all; they were tedious to test and debug; they were difficult to extend and enhance; and overall, they were maintenance nightmares.

Java's introduction with cross-platform portability and the Java servlet model, which streamlined browser-server (request-response) interactions, sparked a revolution in the Web tier. Since the servlet specification's introduction, we've seen multiple advances in Web tier technology, each extending the capabilities and effectiveness of the last. The release of the Java 2 Platform, Enterprise Edition (J2EE) 1.4 contains the latest versions of these technologies: servlets, JavaServer Pages (JSP), JavaServer Pages Standard Tag Library (JSTL), and JavaServer Faces (JSF).

J2EE Web tier technologies are the focus of numerous sessions at JavaOne this week. This article discusses those technologies and describes design patterns and guidelines for making the technologies work together.

J2EE Tiered Architecture
J2EE Web applications are usually broken into three distinct tiers: the business tier, the integration tier, and the Web tier. The business tier represents the business-level logic and coordinates the interactions between the components of the integration tier and the Web tier. The integration tier contains all the "back-end" systems: database systems, legacy systems, external services, and other enterprise integration systems (EISs). The Web tier contains the layer of software that interacts with users of the enterprise application (humans or other enterprise apps). The Web tier is also called the presentation tier, but because it has moved beyond rendering HTML for human users into XML and Web services, "Web tier" seems to better describe this tier's responsibilities.

The Java servlet model was the first J2EE Web tier technology introduced. It started the Web tier revolution by providing several powerful abstractions in an efficient request-response framework. The model is efficient because it separated the request processing from session handling based on the Strategy and Flyweight design patterns: The same instance of a servlet object can be used by many requests by many users, so a new instance of the servlet doesn't need to be created and initialized for each individual request. You accomplish this by storing the session data in a separate object in the servlet container.