Thursday, August 20, 2009

JSF Life Cycle

The six phases of the JSF application lifecycle are as follows (note the event processing at each phase):
  1. Restore View
  2. Apply request values; process events
  3. Process validations; process events
  4. Update model values; process events
  5. Invoke application; process events
  6. Render response

The six phases show the order in which JSF typically processes a form GUI. The list shows the phases in their likely order of execution with event processing at each phase, but the JSF lifecycle is hardly set in stone. You can change the order of execution by skipping phases or leaving the lifecycle altogether. For example, if an invalid request value were copied to a component, the current view would be redisplayed, and some of the phases might not execute. In this case, you could issue a FacesContext.responseComplete method invocation to redirect the user to a different page, then use the request dispatcher (retrieved from the request object in the FacesContext) to forward to an appropriate Web resource. Alternately, you could call FacesContext.renderResponse to re-render the original view.

Focusing your efforts

Some developers using JSF may never write a component or extend the framework, while others may focus on just those tasks. While the JSF lifecycle will be the same for almost any project, you'll likely tap into it at different stages based on your role in the project. If you're concentrating more on the overall application development, you'll likely be concerned with the middle phases of the request processing lifecycle:
  • Apply requests values
  • Process validations
  • Update model values
  • Invoke application
If you're concentrating on JSF component development, you'll probably focus on the first and last phases of the lifecycle:
  • Restore view
  • Render response
In the sections that follow, I'll walk you through every phase of the JSF request processing lifecycle, including event handling and validation. Once you have a basic understanding of each phase, I'll introduce a sample application that shows how they all come together. Before we get started, take a look at Figure 1, a diagram of the JSF lifecycle.
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