Why was "immediate" attribute added to the EditableValueHolders?

Question

Initially immediate flag was only intended for ActionSource interface. But later on it was added to the EditableValueHolder interface also. What was the reason for design decision ?

Answer 1

It's to be used to prioritize validation on several EditableValueHolder components in the same form.

Imagine a form containing input components with immediate="true" as well as input components without this attribute. The immediate inputs will be validated during apply request values phase (which is one phase earlier than usual). The non-immediate inputs will be validated during validations phase (which is the usual phase). If validation fails for at least one of the immediate inputs, then the non-immediate inputs won't be converted/validated at all and thus won't generate any conversion/validation error messages. This is particularly useful in forms with complex validation rules where it doesn't make sense to validate component Y when validation for (immediate) component X has failed anyway.

When used in combination with immediate="true" on a command button in the same form, this will cause all non-immediate inputs being completely skipped. A good real world example is a login form with 2 fields "username" and "password" with required="true" and 2 buttons: "login" and "password forgotten". You could put immediate="true" on the "username" field and the "password forgotten" button to skip the required="true" check on the password field.

In the dark JSF 1.x ages, the immediate="true" was also often (ab)used as a hack in combination with valueChangeListener and FacesContext#renderResponse(), more than often in cascading dropdown lists. Long story short, here's an old blog article on that. To the point, it enables developers to execute a backing bean method on change of a <h:selectOneMenu> without that all other inputs in the same form are been validated. But these days, with the ajax awesomeness, this hack is unnecessary. You can find a concretre example of this case at the bottom of our <h:selectOneMenu> wiki page.

These days, the immediate="true" is still often (ab)used in order to have a specific button which completely bypasses all other inputs, such as a logout button in a "God-form" antipattern (whereby everything is been thrown together in a huge <h:form>), or a cancel button which incorrectly submits the form. Such a button would break when you start to actually need the immediate="true" the right way on one of the inputs. You'd better put such a logout button in its own form, or to change it to process only itself (process="@this" in PrimeFaces). And you'd better change such a cancel button to just refresh the page synchronously by <h:button value="Cancel" />. This works fine if the form is tied to a request/view scoped bean and browser caching is disabled on dynamic pages.

See also:

• Should immediate="true" never be used when dealing with an AJAXified JSF 2.0 component?
• Trying to understand immediate="true" skipping inputs when it shouldn't