zk controller

package login;

import org.apache.poi.ss.usermodel.Textbox;

import org.zkoss.zk.ui.Component;
import org.zkoss.zk.ui.event.Event;
import org.zkoss.zk.ui.select.SelectorComposer;
import org.zkoss.zk.ui.select.annotation.Listen;
import org.zkoss.zk.ui.select.annotation.VariableResolver;
import org.zkoss.zk.ui.select.annotation.Wire;
import org.zkoss.zk.ui.select.annotation.WireVariable;
import org.zkoss.zul.Messagebox;
import org.zkoss.zul.Window;
public class Login extends SelectorComposer<Component> {

    /**
     *
     */

    private static final long serialVersionUID = -1082957709625475807L;

    /**
     *
     */
    @Wire("#win")
    private Window win;

    @Wire("#user")
    private Textbox  user;

    @Wire("#pass")
    private Textbox  pass;
    public void doAfterCompose(Window comp) throws Exception {
          super.doAfterCompose(comp); //wire variables and event listners
          //do whatever you want (you could access wired variables here)
       }
    @Listen("onClick=#submit")
        public void submit(Event event) { //register a listener to a component called retrieve
        if (this.pass==null)
        Messagebox.show("è null");
        }
}