Understanding JSF Life Cycle

The JSF lifecycle phases use a UI component tree to manage the display of the faces components. This tree is a runtime representation of a JSF page: each UI component tag in a page corresponds to a UI component instance in the tree. The FacesServlet servlet manages the request processing lifecycle in JSF applications. FacesServlet creates an object called FacesContext, which contains the information necessary for request processing, and invokes an object that executes the lifecycle.

The JSF Life Cycle is represented by the following diagram:

Photo Courtesy: Web User Interface Developer's Guide for Oracle ADF

Let’s understand each phase of the JSF lifecycle:

·         Restore View: The component tree mentioned earlier is established. If this is not the initial rendering, the tree is restored with the appropriate state. If this is the initial rendering, the component tree is created and the lifecycle jumps to the Render Response phase.

·         Apply Request Values: Each component in the tree extracts new values from the request parameters and stores the values locally. If a component has its immediate attribute set to true, then the validation, the conversion, and the events associated with the component are processed during this phase.

·         Process Validations: It is one of the most important phases of JSF life cycle. The process validation is done through the following steps:

§  Conversion: The local values of components are converted from the input type to the underlying data type.

§  Required Check: If there are no failures in conversion, the required attribute on the component is checked. If the value is true then it goes for validation.

§  Validation: If the required check condition is true, and the associated field contains a value, then any associated validators are run. If the value is true and there is no field value, this phase completes (all remaining validators are executed), but the lifecycle jumps to the Render Response phase.

Condition checking in Validation Process Phase

·         Update Model Values: The component’s validated local values are moved to the model, and the local copies are discarded.

·         Invoke Application: Application-level logic (such as event handlers) is executed

·         Render Response: The components in the tree are rendered. State information is saved for subsequent requests and for the Restore View phase.