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Go with the flow

Build Web applications with Webflow components

By Brian Pontarelli and Grant Zemont, JavaWorld.com, 02/14/03

Webflow is the core of the BEA WebLogic Portal framework. BEA WebLogic Portal encompasses many components including user management, commerce, entitlements, and campaigns. Web applications built with BEA WebLogic Portal can leverage the Webflow system to help separate the presentation logic and the underlying business processes.

The Model-View-Controller 2 (MVC2) pattern is the foundation of Webflow's architecture. Webflow functions mostly as a controller, but it also provides basic model support and includes tag libraries for the view. Unlike most other controller systems, Webflow is more like a workflow system. It provides the ability to chain multiple business logic classes together and supports branching. It builds on the event and handler concept of other controller systems, like Struts, but provides more functionality through chaining and branching based on events.

Web applications can leverage Webflow's functionality to set up event, logic, and site flows. Webflow's "flow" begins at a presentation node (JavaServer Pages (JSP)) and continues through zero or more classes (event handlers called InputProcessors) until another presentation node is encountered. This design makes Webflow a powerful tool for building Web applications.

Webflow's key features include:

• Component-based structure encourages code reuse; frontend, middle-tier, and backend components are all addressed
• Java 2 Platform, Enterprise Edition (J2EE) compliance
• Built-in form validation
• Inherent separation between responsibilities of frontend and backend developers

Let's examine each component and then discuss some best practices for Webflow development.

Note: You can download this article's source code from Resources.

Webflow components

A Webflow is composed entirely of nodes. A node is an abstract component that represents an object in a Web application. Nodes are interconnected by transitions (events). A simple Webflow can illustrate this:

Origin JSP -> Input processor -> Destination JSP

Each arrow in the illustration is an event processed by the Webflow system. Therefore, a Webflow is a string of connected nodes that outlines a logical flow of a part of a Web application. This section briefly describes the types of nodes and other concepts that compose the Webflow framework. We will not rehash existing BEA documentation here. In-depth information about these components can be found on BEA Systems' Website (see Resources).

Presentation nodes

Presentation nodes represent components that allow users to interact with a Web application. Some examples include JSP, HTML, Wireless Markup Language (WML), or servlets.

InputProcessor nodes

These nodes are Java classes that implement the InputProcessor interface. As a result, InputProcessors must implement the following method:

   public Object process(HttpSerlvetRequest request, Object requestContext) throws ProcessingException

The HttpServletRequest object is the request submitted to the WebLogic application server from a client. This request derives from the presentation node that preceded the InputProcessor. In the simple Webflow example above, a form or anchor tag in the Origin JSP creates the request that passes to the InputProcessor. The requestContext is a unique identifier for the request.