hibernate 简单实例出错

import org.hibernate.Transaction;


public class HibernateDAOTest {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
EchoMessageDAO dao=new EchoMessageDAO();
Transaction tran=dao.getSession().beginTransaction();
EchoMessage bean=new EchoMessage();
bean.setMsg("Hibernate message");
dao.save(bean);
();
java.util.List<EchoMessage> results=dao.findAll();
for(int i=0;i<results.size();i++)
{
    
    System.out.println(results.get(1));
    System.out.println(results.get(2));
}
dao.getSession().close();
    }
}

报错：
log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Exception in thread "main" java.lang.NullPointerException
    at HibernateDAOTest.main(HibernateDAOTest.java:18)