JSF has become a popular framework for stateful Web applications, not the least because JSF is an officially blessed JCP standard with at least two implementations: Sun's reference implementation and Apache's MyFaces.

Defining page navigation is among the most common tasks JSF developers must perform. According to the JSF specs, page navigation describes rules and actions that are taken when a user clicks on a button or a URL link. Most JSF applications define navigation rules in a faces.xml file (examples of JSF navigation rules are presented in the Navigation chapter of Sun's JSF tutorial).

Some developers have noted the challenges associated with JSF's navigation model. Ignacio Coloma, for instance, bemoaned the difficulty of managing navigation in the context of JSF's stateful model:

Then the hell of linking pages together starts.... Faces saves the view state between requests, which is dumb if you are working with persistent data. If you dare to use Hibernate, expect all kind of funny behaviour as a request tries to initialize some lazy relationship of a bean retrieved like two clicks ago. If you must refresh data with each request where is the fun of using a stateful view? Remember that it cannot be disabled easily...

According to an article by Interface21's Keith Donald, What Spring Web Flow Offers JSF Developers, Spring Web Flow can make navigation a lot easier task to implement for JSF applications. Donald is a lead developer of Spring Web Flow:

When used as a JSF extension, Spring Web Flow takes over two responsibilities: handling your view navigation rules and managing the state associated with your ongoing user interactions (a.k.a conversations).

This integration combines Web Flow's strengths in navigation and state management with JSF's strength as a growing ecosystem of user interface component libraries. All JSF components and views continue to work as before with Web Flow in the picture. With Web Flow in there, JSF developers benefit from a considerably more powerful navigation model that alleviates the headaches traditionally associated with managing conversational state manually.

Donald further explains that,

The unit of controller functionality in Spring Web Flow—something like an Account registration wizard or a Customer Master/Detail Editor—is called a flow definition. A runtime instance of such a controller is called a flow execution. A new flow execution is launched at runtime to allow a single user to participate in a dialog with the application. The flow execution handles selecting the user's initial view, then responds to user events to carry out application behaviors and determine the next views to display. It also manages the state associated with the user dialog...

A big part of integrating Web Flow with JSF was fitting its flow execution lifecycle into the JSF lifecycle. This was achieved in part by implementing a custom PhaseListener that handles launching new flow executions when requested by a clients, as well as restoring existing flow executions during the restoration of JSF views.

Once integrated with a JSF application, Donald points out how Spring Web Flow can provide several navigation features that would be more difficult to code up with just plain JSF:

• The ability to implement dynamic navigation rules that are changeable on-the-fly without a server restart
• Full forward, backward, refresh, redirect, and recursive navigation capabilities built into its flow definition language
• Modularization and encapsulation of navigation logic through the flow definition concept... Web Flow can be used as a complete replacement for JSF's default "forward-centric" navigation mode

Donald also notes that work is already under way on Spring Web Flow 1.1:

Greater levels of integration is a major theme in an exciting roadmap. Notable on the JSF front, we will be adding support for the Unified Expression Language (EL) within flow definitions, as well as support for leveraging Spring 2.0 as a comprehensive provider of JSF managed-beans beans across all scopes—including the conversational scopes provided by Spring Web Flow...

What are your favorite frameworks or techniques to implement navigation in a Web application?