The Lifecycle of the hello Application

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.

It is not necessary for the beginning user to understand the lifecycle of a JavaServer Faces application, but the information can be useful for creating more complex applications.

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.

• Backing 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 hello example application goes through the following stages when it is deployed on the GlassFish Server.

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

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

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

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

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 more detailed information on the JavaServer Faces lifecycle, see the JavaServer Faces Specification, Version 2.0.