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 while others require you to manage them manually.
By default, JavaServer Faces handles most of the lifecycle actions for you automatically. But it does expose the different parts 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, and 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 response to the client. Rendering, typically is 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 helloWorld example application goes through the following stages when it is deployed on the Enterprise Server:
When the helloWorld application is built and deployed on the Enterprise Server, the application is at an uninitiated state.
When a client makes a first (initial) request for the beanhello.xhtml web page, the helloWorld Facelets application is compiled.
The compiled Facelets application is executed and a new component tree (UIViewRoot) is constructed for the helloWorld application and is placed in the Faces Context.
The component tree is populated with the component and the backing bean property associated with it (represented by the EL expression hello.world).
A new view is built based on the component tree.
The view is rendered to the requesting client as a response.
The component tree is destroyed automatically.
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 document.