how to get values from database to listbox with jpa query

asked 2010-12-26 22:44:06 +0800

yaryan997
210 ● 2

Hi..
Friend

I am very new to Zk framework.

Currently I am doing project with the combination of JPA 2.0 with Hibernate and Spring Framework

I am able to write my queries in JP QL but it throws me the following error

java.lang.NullPointerException
com.app.frontend.SellerWindow.getProducts(SellerWindow.java:55)
com.app.frontend.SellerWindow.onCreate(SellerWindow.java:45)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
java.lang.reflect.Method.invoke(Unknown Source)
org.zkoss.zk.ui.impl.EventProcessor.process0(EventProcessor.java:211)
org.zkoss.zk.ui.impl.EventProcessor.process(EventProcessor.java:141)
org.zkoss.zk.ui.impl.EventProcessingThreadImpl.process0(EventProcessingThreadImpl.java:519)
org.zkoss.zk.ui.impl.EventProcessingThreadImpl.run(EventProcessingThreadImpl.java:446)

my DAO class in given below BasicDAO.java CLASS

package org.com.app.dao;
import org.apache.log4j.PropertyConfigurator;
import org.apache.log4j.Category;

import java.util.List;
import java.util.Iterator;

import javax.ejb.Stateless;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;

import com.app.backend.Product;

/**
* Common persistence methods
* @author icoloma
*/
@Stateless
public class BasicDAO {

@PersistenceContext(unitName="MyProject")
private EntityManager entityManager;
//private EntityTransaction tr =null;

public void setEntityManager(EntityManager entityManager) {
this.entityManager = entityManager;
}

public EntityManager getEntityManager() {
return entityManager;
}

@SuppressWarnings("unchecked")
public List<Product> getProducts() {
// TODO Auto-generated method stub
Query query = entityManager.createQuery("SELECT p.name FROM Product AS p");
System.out.println(query);
List<Product> products = query.getResultList();
return products;
}

}

My SERVICE LAYER HAS CatalogFacade.JAVA CLASS

/**
*
*/
package com.app.service;

import java.util.List;

import javax.ejb.Stateless;

import org.com.app.dao.BasicDAO;

import com.app.backend.Product;

/**
* @author aryan
*
*/
@Stateless
public class CatalogFacade {

protected BasicDAO basicDao;

/**
* @return the basicDao
*/
public BasicDAO getBasicDao() {
return basicDao;
}

/**
* @param basicDao the basicDao to set
*/
public void setBasicDao(BasicDAO basicDao) {
this.basicDao = basicDao;
}

public List<Product> getProducts() {
// TODO Auto-generated method stub
List<Product> products = this.basicDao.getProducts();
return products;
}
}

and MY controller Class is SellerWindow.java CLASS

/**
*
*/
package com.app.frontend;

import java.util.List;
import java.util.Iterator;

import org.zkoss.zk.ui.event.Event;
import org.zkoss.zul.ListModel;
import org.zkoss.zul.ListModelList;
import org.zkoss.zul.Listbox;
import org.zkoss.zul.Window;

import com.app.backend.Product;
import com.app.service.CatalogFacade;

/**
* @author aryan
*
*/
public class SellerWindow extends Window{

/**
*
*/
private static final long serialVersionUID = 1L;

protected CatalogFacade catalogFacade;
/**
* @return the catalogFacade
*/
public com.app.service.CatalogFacade getCatalogFacade() {
return catalogFacade;
}

/**
* @param catalogFacade the catalogFacade to set
*/
public void setCatalogFacade(com.app.service.CatalogFacade catalogFacade) {
this.catalogFacade = catalogFacade;
}

public void onCreate(Event evt) {
ListModel model = new ListModelList(getProducts());
Listbox lbx = (Listbox)getFellow("products");
lbx.setModel(model);
lbx.setSelectedIndex(0);

lbx.focus();
}

public List<Product> getProducts(){

return this.catalogFacade.getProducts();
}
}

I don't able to understand why this error is coming..
plz help me to get out of this..

thanx in advance.