public Object findByPK( Class clazz, Serializable key ) throws DAOException, InvalidDataException {
   Object result = null;

   if ( null == key ) {
       throw new InvalidDataException( "Attempted a find operation with a null key");
   }

   try {
       Session session = HibernateUtil.getSession();
       HibernateUtil.beginTransaction();

       result = session.get( clazz, key );

       HibernateUtil.commitTransaction();

   } catch ( HibernateException he ) {
       String message = "Failed to find [" + clazz.getName() + "] by primary key";
       log.error( message, he  );
       HibernateUtil.rollbackTransaction();
       throw new DAOException( message , he );
   } finally {
       HibernateUtil.closeSession();
   }

   return result;
    }

    public static Session getSession() throws DAOException {
   Session s = (Session) threadSession.get();
   // Open a new Session, if this thread has none yet
   try {
       if (s == null) {
      s = sessionFactory.openSession();
      s.setFlushMode( FlushMode.COMMIT );
      threadSession.set(s);
      log.debug( "Fetched session." );
       } else {
      log.debug( "Fetched pre-existing session." );
       }
   } catch (HibernateException ex) {
       log.error("getSession", ex );
       ex.printStackTrace();
       throw new DAOException(ex);
   }
   return s;
    }


    public static void closeSession() throws DAOException {
   try {
       Session s = (Session) threadSession.get();
       threadSession.set(null);
       if (s != null && s.isOpen()) {
      log.debug( "Closing session." );
      s.flush();
      s.close();
       }
   } catch (HibernateException ex) {
       log.error( "closeSession", ex );
       ex.printStackTrace();
       throw new DAOException(ex);
   }
    }


    public static void beginTransaction() throws DAOException {
   Transaction tx = (Transaction) threadTransaction.get();
   
   try {
       if (tx == null) {
      tx = getSession().beginTransaction();
      threadTransaction.set(tx);
      log.debug( "Starting new transaction." );      
       } else {
      log.debug( "Joining transaction in progress." );      
       }
   } catch (HibernateException ex) {
       log.error( "beginTransaction", ex );
       ex.printStackTrace();
       throw new DAOException(ex);
   }
    }


    public static void commitTransaction() throws DAOException {
   Transaction tx = (Transaction) threadTransaction.get();
   try {
       if ( tx != null && !tx.wasCommitted()
       && !tx.wasRolledBack() ){
      tx.commit();
      log.debug( "Commiting transaction." );      
       } else {
      log.debug( "CommitTransaction called but no transaction was in progress." );
       }
       threadTransaction.set(null);
   } catch (HibernateException ex) {
       log.error( "commitTransaction", ex );
       ex.printStackTrace();
       rollbackTransaction();
       throw new DAOException(ex);
   }
    }