A Validator implementation is a class that can perform validation (correctness checks) on a EditableValueHolder. Zero or more Validators can be associated with each EditableValueHolder in the view, and are called during the Process Validations phase of the request processing lifecycle.

Individual Validators should examine the value and component that they are passed, and throw a ValidatorException containing a FacesMessage, documenting any failures to conform to the required rules.

For maximum generality, Validator instances may be configurable based on properties of the Validator implementation class. For example, a range check Validator might support configuration of the minimum and maximum values to be used.

Validator implementations must have a zero-arguments public constructor. In addition, if the Validator class wishes to have configuration property values saved and restored with the view, the implementation must also implement StateHolder.

If the class implementing Validator has a ResourceDependency annotation, the action described in ResourceDependency must be taken when EditableValueHolder.addValidator(javax.faces.validator.Validator) is called. If the class implementing Validator has a ResourceDependencies annotation, the action described in ResourceDependencies must be taken when EditableValueHolder.addValidator(javax.faces.validator.Validator) is called.