a different object with the same identifier value was already associated with the session

这个问题,我把对象赋值为NULL,也是很好用的.在我的系统中,更新好用了,可是插入不好用了.没改前,是插入好用,而更新不好用.本来是系统中的问题,可是,catch只是捕捉到,从但是,没有把log打印出来,找原因实在是难找.在高度数据库时,最好把异常捕捉中的信息打印出来.org.springframework.orm.hibernate.HibernateSystemException: a different object with the same identifier value was already associated with the session: 4443398, of class: com.onewaveinc.media.cms.entity.SyncImportFolder; nested exception is net.sf.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: 4443398, of class: com.onewaveinc.media.cms.entity.SyncImportFolder
net.sf.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: 4443398, of class: com.onewaveinc.media.cms.entity.SyncImportFolder
at net.sf.hibernate.impl.SessionImpl.doSave(SessionImpl.java:852)
at net.sf.hibernate.impl.SessionImpl.saveWithGeneratedIdentifier(SessionImpl.java:790)
at net.sf.hibernate.impl.SessionImpl.save(SessionImpl.java:749)
at org.springframework.orm.hibernate.HibernateTemplate$9.doInHibernate(HibernateTemplate.java:555)
at org.springframework.orm.hibernate.HibernateTemplate.execute(HibernateTemplate.java:363)
at org.springframework.orm.hibernate.HibernateTemplate.save(HibernateTemplate.java:552)
at com.onewaveinc.media.cms.dao.impl.SyncFolderHibernateDao.insertHavaIndex(SyncFolderHibernateDao.java:31)
at com.onewaveinc.media.cms.manager.SyncFolderManager.doImportSyncFolder(SyncFolderManager.java:193)
at com.onewaveinc.media.cms.manager.SyncFolderManager.insertHavaIndex(SyncFolderManager.java:107)
at com.onewaveinc.media.cms.manager.SyncFolderManager.importSyncFolderList(SyncFolderManager.java:607)
at com.onewaveinc.media.cms.web.SyncFolderImportAction.post(SyncFolderImportAction.java:41)
at com.onewaveinc.media.common.web.HttpMethodAction.execute(HttpMethodAction.java:36)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:421)
at com.onewaveinc.media.web.struts.MediaRequestProcessor.processActionPerform(MediaRequestProcessor.java:51)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:226)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1164)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:415)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:237)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)
at org.ajaxanywhere.AAFilter.doFilter(AAFilter.java:41)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:186)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)
at com.onewaveinc.appcommon.security.web.utils.SecurityFilter.doFilter(SecurityFilter.java:89)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:186)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)
at org.springframework.orm.hibernate.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:174)
at com.onewaveinc.media.common.web.SpringHibernateSessionFilter.doFilterInternal(SpringHibernateSessionFilter.java:50)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:186)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)
at com.onewaveinc.media.web.struts.StrutsValidateFilter.doFilter(StrutsValidateFilter.java:38)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:186)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)
at com.onewaveinc.appcommon.utils.web.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:168)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:186)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:214)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:152)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:118)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:102)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardEngin.ve.invoke(StandardEngin.ve.java:109)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:929)
at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:160)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:799)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:705)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:577)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:683)
at java.lang.Thread.run(Thread.java:534)



a different object with the same identifier value was already associated with the session
一个经典的hibernate错误:a different object with the same identifier value was already associated with the session xxxx
hibernate3.0以上使用merge()来合并两个session中的同一对象
具体到我自己的代码就是
public Object getDomain(Object obj) {
  getHibernateTemplate().refresh(obj);
  return obj;
  }
  public void deleteDomain(Object obj) {
  obj = getHibernateTemplate().merge(obj);
  getHibernateTemplate().delete(obj);
  }


解决a different object with the same identifier value was already associated with the session错误 

这个错误我一共遇到过两次，一直没有找到很好的解决方案，这个错误产生原因相信大家都知道，因为在hibernate中同一个session里面有了两个相同标识但是是不同实体，当这时运行saveOrUpdate(object)操作的时候就会报这个错误。呵呵，也许你会说，你这么说跟没说没什么区别，我承认，呵呵，我不知道具体为什么会产生这个错误，要不然也不会很久都没有解决，现在，给出一个临时的解决方案，给向我一样，没有办法找到根源的人一个能够继续执行下去的方法（当然是对的，只是不是从产生原因入手）

其实要解决这个问题很简单，只需要进行session.clean()操作就可以解决了，但是你在clean操作后面又进行了saveOrUpdate(object)操作，有可能会报出"Found two representations of same collection"，我找了很多资料，没有什么很好的解释，其中这篇文章帮助最大[url]http://opensource.atlassian.com/projects/hibernate/browse/HHH-509[/url]。

最后通过session.refresh(object)方法就可以解决了，注意，当object不是数据库中已有数据的对象的时候，不能使用session.refresh(object)因为refresh是从hibernate的session中去重新取object，如果session中没有这个对象，则会报错所以当你使用saveOrUpdate(object)之前还需要判断一下

当然这个问题最容易解决的办法还是使用Hibernate里面自带的merge()方法。不过我始终觉得碰到问题就用这种软件自带的非常用方法（和saveOrUpdate()，save(),update()相比）感觉十分不爽。

后来我还发现这种错误经常出现在一对多映射和多对多映射，请大家在使用一对多和多对多映射的时候要小心一些


Hibernate 疑难异常及处理


1、a different object with the same identifier value was already associated with the session。

　　错误原因：在hibernate中同一个session里面有了两个相同标识但是是不同实体。

　　解决方法一：session.clean()

　　PS：如果在clean操作后面又进行了saveOrUpdate(object)等改变数据状态的操作，有可能会报出"Found two representations of same collection"异常。

　　解决方法二：session.refresh(object)

　　PS：当object不是数据库中已有数据的对象的时候，不能使用session.refresh(object)因为该方法是从hibernate的session中去重新取object，如果session中没有这个对象，则会报错所以当你使用saveOrUpdate(object)之前还需要判断一下。

　　解决方法三：session.merge(object)

　　PS：Hibernate里面自带的方法，推荐使用。

2、Found two representations of same collection

　　错误原因：见1。

　　解决方法：session.merge(object)

以上两中异常经常出现在一对多映射和多对多映射中


a different object with the same identifier value was already associated with the session
一个经典的hibernate错误:a different object with the same identifier value was already associated with the session xxxx
hibernate3.0以上使用merge()来合并两个session中的同一对象
具体到我自己的代码就是
public Object getDomain(Object obj) {
  getHibernateTemplate().refresh(obj);
  return obj;
  }
  public void deleteDomain(Object obj) {
  obj = getHibernateTemplate().merge(obj);
  getHibernateTemplate().delete(obj);
  }

====================我是分割线===================

其实我的解决办法是把obj给重新merge一下,注意红字部分

public Serializable save(Object persistentObject) throws DaoException {
  try {
        
  Session session = this.openSession();
  beginTransaction();
  persistentObject = session.merge(persistentObject);
  Serializable id = session.save(persistentObject);
  if (autoCommit)
  commitTransaction();
  return id;
  } catch (HibernateException ex) {
  log.error("Fail to save persistentObject", ex);
  throw new DaoException("Fail to save persistentObject", ex);
  } finally {
  if (autoCloseSession)
  closeSession();
  }
  }