UIInput components and command components (those that implement ActionSource, such as buttons and hyperlinks) can set the immediate attribute to true to force events, validations, and conversions to be processed during the apply request values phase of the life cycle. Page authors need to carefully consider how the combination of an input component’s immediate value and a command component’s immediate value determines what happens when the command component is activated.
Assume that you have a page with a button and a field for entering the quantity of a book in a shopping cart. If both the button’s and the field’s immediate attributes are set to true, the new value of the field will be available for any processing associated with the event that is generated when the button is clicked. The event associated with the button and the event, validation, and conversion associated with the field are all handled during the apply request values phase.
If the button’s immediate attribute is set to true but the field’s immediate attribute is set to false, the event associated with the button is processed without updating the field’s local value to the model layer. This is because any events, conversion, or validation associated with the field occurs during its usual phases of the life cycle, which come after the apply request values phase.
The bookshowcart.jsp page of the Duke’s Bookstore application has examples of components using the immediate attribute to control which component’s data is updated when certain buttons are clicked. The quantity field for each book has its immediate attribute set to false. (The quantity fields are generated by the UIData component. See Using Data-Bound Table Components, for more information.) The immediate attribute of the Continue Shopping hyperlink is set to true. The immediate attribute of the Update Quantities hyperlink is set to false.
If you click the Continue Shopping hyperlink, none of the changes entered into the quantity input fields will be processed. If you click the Update Quantities hyperlink, the values in the quantity fields will be updated in the shopping cart.