JSF validate on submit form - validation

Question

I'm working on a JSF 2.0 form, I have a managedbean with 2 fields
import java.util.Date;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.RequestScoped;
#ManagedBean
#RequestScoped
public class StackOverflow {
private Date firstDate;
private Date secondDate;
public void submit(){
//validate here and show error on form
}
}
and the xhtml like:
<h:inputText value="#{stackOverflow.firstDate}">
<f:convertDateTime pattern="d/M/yyyy" />
</h:inputText>
<h:inputText value="#{stackOverflow.secondDate}">
<f:convertDateTime pattern="d/M/yyyy" />
</h:inputText>
<h:commandLink action="#{stackOverflow.submit}">
<span>Submit</span>
</h:commandLink>
I want to validate the first and second date that the second date is not before the first date

Answer 1

Here's one of the ways:
<h:messages globalOnly="true"/>
<h:form>
<h:inputText value="#{stackOverflow.firstDate}" binding="#{firstDate}">
<f:convertDateTime pattern="d/M/yyyy" />
</h:inputText>
<h:inputText value="#{stackOverflow.secondDate}" validator="dateValidator">
<f:attribute name="firstDate" value="#{firstDate}" />
<f:convertDateTime pattern="d/M/yyyy" />
</h:inputText>
<h:commandButton value="Submit" action="#{stackOverflow.submit}"/>
</h:form>
with
#FacesValidator(value="dateValidator")
public class DateValidator implements Validator {
#Override
public void validate(FacesContext context, UIComponent component, Object value) throws ValidatorException {
UIInput sd = (UIInput)component.getAttributes().get("firstDate");
Date firstDate = (Date)sd.getValue();
Date secondDate = (Date)value;
if(!firstDate.before(secondDate)){
FacesMessage msg = new FacesMessage("Entered dates are invalid: first date must be before second date");
throw new ValidatorException(msg);
}
}
}