<zk>
	<window id="win" apply="test.DateController" >
		<datebox id="dob" width="200px" visible="true" format="yyyy/MM/dd" lenient="false"/>
		<label id="doberr" />
	</window>
</zk>

package test;

import org.zkoss.zk.ui.Component;
import org.zkoss.zk.ui.util.GenericForwardComposer;
import org.zkoss.zul.Datebox;
import org.zkoss.zul.Label;

public class DateController extends GenericForwardComposer {
	private static final long serialVersionUID = 1L;

	// Form fields; auto-wired.
	private Datebox dob;
	private Label doberr;

	public void doAfterCompose(Component comp) throws Exception{
		super.doAfterCompose(comp);
		dob.setConstraint(new MyDateConstraint(doberr, MyDateConstraint.STRICT
				| MyDateConstraint.SERVER | MyDateConstraint.NO_FUTURE
				| MyDateConstraint.NO_TODAY));

	}
}

package test;

import org.zkoss.util.logging.Log;
import org.zkoss.zk.ui.Component;
import org.zkoss.zk.ui.WrongValueException;
import org.zkoss.zul.CustomConstraint;
import org.zkoss.zul.Datebox;
import org.zkoss.zul.Label;
import org.zkoss.zul.SimpleDateConstraint;

public class MyDateConstraint extends SimpleDateConstraint implements CustomConstraint{
	
	private static final long serialVersionUID = 1L;
	private static Log log = Log.lookup(MyDateConstraint.class);
	private Label errfld;

	public MyDateConstraint(Label errlbl, int flags) {
		super(flags);
		errfld = errlbl;
	}
	
	public void showCustomError(Component comp, WrongValueException ex) {
		System.out.println("showCustomError");
		if (ex != null) {
			log.debug("WrongValueException Message: " + ex.getMessage());
			errfld.setValue(ex.getMessage());
			errfld.setVisible(true);
		} else {
			log.debug("No exception");
			if (comp instanceof Datebox) {
				log.debug("datebox error message is: "
						+ ((Datebox) comp).getErrorMessage());
			} else
				log.debug("comp is: " + comp.getClass().getName());

			errfld.setVisible(false);
		}
	}

}