hibernate 为什么会无法使用HibernateUtil.currentSession和 HibernateUtil.closeSession()

import org.hibernate.Session;

import org.hibernate.Transaction;



import net.sf.ehcache.hibernate.HibernateUtil;



public class PersonManager {

	public static void main(String [] args)

	{

		Session session = HibernateUtil.currentSession();

		Transaction tx = session.beginTransaction();

		Person p = new Person();

		Address a = new Address("Guangzhou tianhe");

		p.setName("crazyit.org");

		p.setAge(21);

		p.setAddress(a);

		session.persist(p);

		Address a2 = new Address("Shanghai hongkou");

		p.setAddress(a2);

		tx.commit();

		HibernateUtil.closeSession();

		

	}

}