【错误】net.sf.hibernate.NonUniqueObjectException

【异常】net.sf.hibernate.NonUniqueObjectException

net.sf.hibernate.NonUniqueObjectException:
a different object with the same identifier value was already associated with the session: .........

今天遇到这样的报错异常，网上搜索答案，以下的代码逻辑就会出现该异常：

SessionFactory sessionFactory= new Configuration().configure().buildSessionFactory();
Session session=sessionFactory.openSession();
User user1=new User("anray");
User user2=new User("anray");

//假设User是一个持久对象，有一个name属性
user1.setName("anray1");
user2.setName("anray2");
session.update(user1);
session.update(user2);

这样的代码，我们一般不可能会这样写，但有时，我们回写一个专门的类来管理sessionFactory和session，如：
package com.cpic.p17.pf.dao;

import org.hibernate.HibernateException;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.classic.Session;

/**
?* Hibernate DAO实现
?* @author fanjf
?* @date 2012-3-22
?*/
public class HibernateDao {
??? private static final SessionFactory sessionFactory;
??? static {
??? ??? try {
??? ??? ??? sessionFactory = new Configuration().configure().buildSessionFactory();
??? ??? } catch (HibernateException ex) {
??? ??? ??? throw new RuntimeException("Exception building SessionFactory: " + ex.getMessage(), ex);
??? ??? }
??? }
???
??? public static final ThreadLocal threadLocal = new ThreadLocal();
???
??? /** 得到当前线程的session */
??? public static final Session getSession() throws HibernateException {
??? ??? Session se = (Session) threadLocal.get();
??? ??? // Open a new Session, if this Thread has none yet
??? ??? if (se == null) {
??? ??? ??? se = sessionFactory.openSession();
??? ??? ??? threadLocal.set(se);
??? ??? }
??? ??? return se;
??? }
???
??? /** 关闭当前线程的session */
??? public static final void closeSession() throws HibernateException {
??? ??? Session s = (Session) threadLocal.get();
??? ??? threadLocal.set(null);
??? ??? if (s != null)
??? ??? ??? s.close();
??? }
???
??? /**
??? ?*保存一个对象到数据库中,使用完后要自己调用closeSession()
??? ?*/
??? public static void create(Object object) throws HibernateException {
??? ??? Session session1 = getSession();
??? ??? Transaction transaction1 = session1.beginTransaction();
??? ??? try {
??? ??? ??? session1.save(object);
??? ??? ??? transaction1.commit();
??? ??? } catch (HibernateException ex) {
??? ??? ??? if (transaction1 != null)
??? ??? ??? ??? transaction1.rollback();
??? ??? ??? closeSession();
??? ??? ??? throw ex;
??? ??? }
??? }
???
??? /**
??? ?*更新一个对象到数据库中，使用完后要自己调用closeSession()
??? ?*/
??? public static void update(Object object) throws HibernateException {
??? ??? Session session1 = getSession();
??? ??? Transaction transaction1 = session1.beginTransaction();
??? ??? try {
??? ??? ??? session1.update(object);
??? ??? ??? transaction1.commit();
??? ??? } catch (HibernateException ex) {
??? ??? ??? if (transaction1 != null)
??? ??? ??? ??? transaction1.rollback();
??? ??? ??? closeSession();
??? ??? ??? throw ex;
??? ??? }
??? }
}

如果在web编程时用这个类的方法来更新一个user对象，在调用了HibernateUse.update(user)后，没有接着调用HibernateUse.closeSession()，其实为了节省资源也不提倡每次操作都调用HibernateUse.closeSession()关闭session；如果对相同的user对象进行又一次的更新时，碰巧容器又分配了同一个thread进行处理，那么得到的也是同一个session，这样就出现了上面的提到了问题，session里的两个user的识别id一样，但内容不一样。

为了解决这个问题可以在update前清空session（不是关闭，这样资源消耗比较少），修改后的公用类如下：
（就是在update()方法里添加了session1.clear();）
??? /**
??? ?*更新一个对象到数据库中，使用完后要自己调用closeSession()
??? ?*/
??? public static void update(Object object) throws HibernateException {
??? ??? Session session1 = getSession();
??? ??? Transaction transaction1 = session1.beginTransaction();
??? ??? try {
??? ??? ??? session1.clear();//更新对象前，清空session

??? ??? ??? session1.update(object);
??? ??? ??? transaction1.commit();
??? ??? } catch (HibernateException ex) {
??? ??? ??? if (transaction1 != null)
??? ??? ??? ??? transaction1.rollback();
??? ??? ??? closeSession();
??? ??? ??? throw ex;
??? ??? }
??? }