JSF Under the Hood—Part 2 - JSF and HTML5 - page 74

Validator Interface
The javax.faces.validator.Validator interface is the core interface for the JSF validators. The JSF Validator
interface describes a Java class that can perform validation (checks on the correctness) on EditableValueHolder
components. A single EditableValueHolder can have zero or more validators in the view. Listing 3-10 shows the JSF
Validator interface.
Listing 3-10. JSF Validator Interface
package javax.faces.validator;
import java.util.EventListener;
import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
public interface Validator extends EventListener {
//...
public void validate(FacesContext context, UIComponent component, Object value) throws
ValidatorException;
}
As shown in the Validator interface, it contains a single API. The validate API performs the required validation
on the parent EditableValueHolder component's value; this API can be called in the Process Validations phase
(or in Apply Request Values phase if immediate attribute of the EditableValueHolder is set to true ). validate() API
has three parameters:
1. context , which represents the JSF FacesContext instance of this request.
2. component , which represents the component whose value will be validated.
This component instance can be used in order to retrieve the component attributes
if the validator needs to use them.
3. value , which represents the String value to be validated.
For every component that has a validator (or more). If the validation fails, the validator must throw
ValidatorException ; in this case, the component that owns the validator will be marked as invalid, and a
ValidatorException message will be received and added to the FacesContext messages in order to be displayed
by the <h:message> component associated with the EditableValueHolder component and by the <h:messages>
component.
Listing 3-11 shows an example to illustrate how validation works for multiple EditableValueHolder components
with attached validators. Notice that in this example, number1 and number2 are attributes in TestBean managed bean
and are of type Long .
Listing 3-11. Validation Example for Multiple EditableValueHolder Components
<h:form>
<h:outputText value="Enter Number1: "/>
<h:inputText id="number1"
value="#{testBean.number1}">
<f:validateRequired/>
<f:validateLongRange minimum="0" maximum="999"/>
</h:inputText>
<h:message for="number1"/>