net.sf.hibernate.NonUniqueObjectException: a different object with the same iden

net.sf.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: .........
这样的问题不知道大家有没有遇到？
SessionFactory sessionFactory= new Configuration().configure().buildSessionFactory();
Session session=sessionFactory.openSession();
User user1=new User("anray");
User user2=new User("anray");
user1.setName("anray1");//假设User是一个持久对象，有一个name属性
user2.setName("anray2");
session.update(user1);
session.update(user2);
这样就会出现上面的异常
看上去上面的代码有点傻，我们编程中不可能出现这样的情况。
但是有一种情况是经常用到的，就是写一个专门的类来管理sessionFactory和session，如下
/*
* Examination System version 0.1
* Data persist layer(Using Hibernate 2.1.2)
* Created on 2004-4-9 11:58:12
*/
package bts.hibernate;
/**
* @author Anray
*/
import net.sf.hibernate.*;
import net.sf.hibernate.cfg.*;
public class HibernateUse
{
  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();）
/*
* Examination System version 0.1
* Data persist layer(Using Hibernate 2.1.2)
* Created on 2004-4-9 11:58:12
*/
package bts.hibernate;
/**
* @author Anray
*/
import net.sf.hibernate.*;
import net.sf.hibernate.cfg.*;
public class HibernateUse
{
  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.clear();
      session1.update(object);
      transaction1.commit();
    }catch(HibernateException ex){
      if(transaction1!=null)transaction1.rollback();
      closeSession();
      throw ex;
    }
  }
}

第一次写东西，大家多指教