How to correctly deal with Hibernate session?

mattjiang · **Joined:** Sat Jan 31, 2004 10:09 am **Posts:** 26

hi experts,

I have two ways to deal with Hibernate session,
1) To close session before ending each request-response cycle, and open new session before starting the same cycle.

2) Just to disconnect() and clear() session before ending each request-response cycle, and reconnect() session before start the same cycle.

Because I still have to reuse the entities and these entities may have lazing loading collections. So I keep them in Visit. Does #2 is more appropriate to match my requirement? Or another way to correctly handle my requirement?

Please advise, thank you all very much.

anthony · **Posted:** Wed Feb 25, 2004 3:41 am

- if you need only one request to do your business --> reconnect a session and "put" it on the threadLocal (many topics deal with it), no need to open/close a session (this is more expensive), a servlet filter is ok to magage it
- if you need more than one request, i advise to use a cache system (jcs is bad, EHcache is ok and pretty simple to use) and the threadlocal strategy.
- if you don't want to use the cache, you may use the HTTPSession to store you hibernateSession, but this strategy is more complexe...

My team use the 3 method and the third was the most complexe to code in our framework

Good luck

christian · **Posted:** Wed Feb 25, 2004 6:13 am

http://www.hibernate.org/Documentation/ ... ctionScope

mattjiang · **Joined:** Sat Jan 31, 2004 10:09 am **Posts:** 26

christian wrote:

http://www.hibernate.org/Documentation/SessionAndTransactionScope

Thank you very much, I ever read this article, and followed the session-per-application-transaction pattern.
But I got into the following Exception:

Code:

Caused by: net.sf.hibernate.HibernateException: [b]You may not dereference a collection with cascade="all-delete-orphan"[/b] 
net.sf.hibernate.impl.SessionImpl.updateUnreachableCollection(SessionImpl.java:2885) 
net.sf.hibernate.impl.SessionImpl.flushCollections(SessionImpl.java:2754) 
net.sf.hibernate.impl.SessionImpl.flushEverything(SessionImpl.java:2225) 
net.sf.hibernate.impl.SessionImpl.autoFlushIfRequired(SessionImpl.java:1769) 
net.sf.hibernate.impl.SessionImpl.getQueries(SessionImpl.java:1536) 
net.sf.hibernate.impl.SessionImpl.find(SessionImpl.java:1501) 
net.sf.hibernate.impl.QueryImpl.list(QueryImpl.java:39) 
hibernate.SessionUtil.executeQuery(SessionUtil.java:107) 

How this exception occured:
1) The entities relationship is Order(one) -- OrderItems(many)
2) I query out a list of Order(s) in the first request/response cycle.
3) From Order(s) query result, result entities stored in HttpSession, I pick one record and launch secend request/response cycle to its items detail.
4) Then the exception is occured.

Below is my Hibernate session controller source, please note that session is not closed. And it will be much appreciated it if you indicate the problem is:

Code:

public class SessionController implements Filter {

   private static ThreadLocal hSessionHolder = new ThreadLocal();
   private static SessionFactory sessionFactory;
   
   static {
      
      Configuration cfg;
      try {
         cfg = new Configuration().configure();
         sessionFactory = cfg.buildSessionFactory();
      }
      catch (HibernateException e) {
         throw new RuntimeException("Fail to configure hibernate", e);
      }
   }
   
   public static Session getSession() {
      
      Session s = (Session) hSessionHolder.get();
      if (s == null || !s.isOpen()) {
         s = initSession();
         hSessionHolder.set(s);
      }
      return s;
   }
   
   public void init(FilterConfig arg0) throws ServletException {
      
      // empty
   }

   public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
      
     final String HSESSION = "hibernate.session";
     
     HttpSession httpSession = ((HttpServletRequest)request).getSession();
     Session session = (Session) httpSession.getAttribute(HSESSION);
      try {
         try {
           if (session == null) {
             session = initSession();
             httpSession.setAttribute(HSESSION, session);
           }
           else {
             if (!session.isConnected())
               session.reconnect();
           }
           
           hSessionHolder.set(session);

            chain.doFilter(request, response);
         }
         finally {
           session = (Session) hSessionHolder.get();
           hSessionHolder.set(null);
           if (session != null) {
             //session.clear();
               session.disconnect();
           }
         }
      }
      catch (HibernateException e) {
        e.printStackTrace();
         throw new RuntimeException("Fail to close hibernate session", e);
      }
   }

   public void destroy() {
      //empty
   }
   
   private static Session initSession() {
      
      Session session;
      try {
         session = sessionFactory.openSession();
         return session;
      }
      catch (HibernateException e) {
        e.printStackTrace();
         throw new RuntimeException("Fail to open hibernate session.");
      }
      
   }
}

anthony · **Posted:** Wed Feb 25, 2004 7:35 am

can you give us the code of your app?
it will be easier

emmanuel · **Posted:** Wed Feb 25, 2004 8:53 am

I think you do

Code:

parent = s.load(PArent.class, id);
s.close();
parent.setDeleteOrphanChildren(new HashSet());
openSession();
s.saveOrUpdate(parent);

This is not allowed, Hibernate keep state of orphan to delete in Hibernate Set implementation.