About Required Values and the immediate Attribute

The required attribute lets you specify whether a value must be supplied for a UIInput component or a component that extends UIInput. If a component must have a non-null value or a String value of at least one character, set the required attribute to true. You can use the required attribute with nested validators on the same component.

When the form is submitted and the value is null or a zero-length string, the component is invalidated and an error message is placed in the queue. If there are other validators registered on the component, they are not called at all and the current page is redisplayed.

Note: If you do not use a required attribute and set it to true, other validators that are registered on the component are called. If the component must have a value, then you have to handle null or zero-length strings in those validators.

When a page has a required input field and a command component say, a "Cancel" button, a validation error will cause the current page to redisplay if the user clicks "Cancel" without filling in a value in the required field. In that case, you need to set the immediate attribute of the command component to true, thereby allowing the command to be executed during the Apply Request Values phase.