Posted by:anray

Posted on:2004-08-01 20:13

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