7.3 A Simple JavaServer Faces Application

JavaServer Faces technology provides an easy and user-friendly process for creating web applications. Developing a simple JavaServer Faces application typically requires the following tasks, which have already been described in A Web Module That Uses JavaServer Faces Technology: The hello1 Example:

• Creating web pages using component tags

• Developing managed beans

• Mapping the FacesServlet instance

The hello1 example includes a managed bean and two Facelets web pages. When accessed by a client, the first web page asks the user for his or her name, and the second page responds by providing a greeting.

For details on Facelets technology, see Chapter 8, "Introduction to Facelets". For details on using EL expressions, see Chapter 9, "Expression Language". For details on the JavaServer Faces programming model and building web pages using JavaServer Faces technology, see Chapter 10, "Using JavaServer Faces Technology in Web Pages".

Every web application has a lifecycle. Common tasks, such as handling incoming requests, decoding parameters, modifying and saving state, and rendering web pages to the browser, are all performed during a web application lifecycle. Some web application frameworks hide the details of the lifecycle from you, whereas others require you to manage them manually.

By default, JavaServer Faces automatically handles most of the lifecycle actions for you. However, it also exposes the various stages of the request lifecycle so that you can modify or perform different actions if your application requirements warrant it.

The lifecycle of a JavaServer Faces application starts and ends with the following activity: The client makes a request for the web page, and the server responds with the page. The lifecycle consists of two main phases: Execute and Render.

During the Execute phase, several actions can take place.

• The application view is built or restored.

• The request parameter values are applied.

• Conversions and validations are performed for component values.

• Managed beans are updated with component values.

• Application logic is invoked.

For a first (initial) request, only the view is built. For subsequent (postback) requests, some or all of the other actions can take place.

In the Render phase, the requested view is rendered as a response to the client. Rendering is typically the process of generating output, such as HTML or XHTML, that can be read by the client, usually a browser.

The following short description of the example JavaServer Faces application passing through its lifecycle summarizes the activity that takes place behind the scenes.

The hello1 example application goes through the following stages when it is deployed on GlassFish Server.

1. When the hello1 application is built and deployed on GlassFish Server, the application is in an uninitiated state.

2. When a client makes an initial request for the index.xhtml web page, the hello1 Facelets application is compiled.

3. The compiled Facelets application is executed, and a new component tree is constructed for the hello1 application and placed in a FacesContext.

4. The component tree is populated with the component and the managed bean property associated with it, represented by the EL expression hello.name.

5. A new view is built, based on the component tree.

6. The view is rendered to the requesting client as a response.

7. The component tree is destroyed automatically.

8. On subsequent (postback) requests, the component tree is rebuilt, and the saved state is applied.

For full details on the lifecycle, see The Lifecycle of a JavaServer Faces Application.