JSF standard validator tags allow the binding attribute (this is also true for listener and converter tags). This means that developers can bind validator implementations to backing bean properties. The main advantages of using the binding facility are:
- The developer can allow to the backing bean to instantiate the implementation
- The backing bean can programmatically access the implementation's attributes
We developed this recipe with NetBeans 6.8, JSF 2.0, and GlassFish v3. The JSF 2.0 classes were obtained from the NetBeans JSF 2.0 bundled library.
To successfully accomplish a binding task, you can follow three simple steps (these steps are true for converter, listener, and validator tags):
- Nest the validator (listener, converter) tag in the component tag.
- Put in the backing bean a property that takes and return the validator (listener, converter) implementation class.
- Reference the backing bean property using a value expression from the
bindingattribute of the validator (listener, converter) tag.
As per the example, let's bind the standard f:validateLongRange validator to a backing bean property. The idea is to let the backing bean set the values for the minimum and maximum attributes. First, you have to register the validator onto the component by nesting the f:validateLongRange tag within the component tag. Then, you have to reference the property with the binding attribute of the f:validateLongRange tag.
<h:form id="IpForm">
<h:outputText value="Insert your age:"/><br />
<h:inputText id="ageID" required="true"
value="#{userBean.userAge}">
<f:validateLongRange binding="#{userBean.longAge}"/>
</h:inputText>
<h:message showSummary="true" showDetail="false" for="ageID"
style="color: red; text-decoration:overline"/>
<br />
<h:commandButton id="submit" action="response?faces-redirect=true"
value="Submit"/>
</h:form>
The longAge property is defined in the following managed bean:
package users;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;
import javax.faces.validator.LongRangeValidator;
@ManagedBean
@SessionScoped
public class UserBean {
private int userAge;
private LongRangeValidator longAge;
public int getUserAge(){
return this.userAge;
}
public void setUserAge(int userAge){
this.userAge=userAge;
}
public LongRangeValidator getLongAge(){
return this.longAge;
}
public void setLongAge(LongRangeValidator longAge){
longAge.setMinimum(18);
longAge.setMaximum(90);
this.longAge=longAge;
}
}
In our example, the backing bean sets the minimum and maximum values within the f:validateLongRange tag, which means that the user's input will be constrained by these boundaries. This time the number's range is indicated without using specific attributes in f:validateLongRange tag. Instead of this, we use the binding attribute to reference the longAge property, which is a LongRangeValidator instance, offering us access to this class's methods.