public class HibernateUtil
{
   // Logger initialization
   private static final Log LOG = LogFactory.getLog(HibernateUtil.class);

   // map that holds sessionFactory
   private static Map<String,SessionFactory> sessionFactory = new HashMap<String,SessionFactory>();
   
   // map that holds current open sessions
   public static final Map<String,ThreadLocal<Session>>session = new HashMap<String,ThreadLocal<Session>>();
   
   public static void initSession(Map<String,List<String>> hbmMap, ClassLoader mainClass)
      throws HibernateException, java.io.IOException {


      //======================================================================================
      // to handle multiple database connections,
      // 1. [instance].db.xml specify db properties
      // 2. mapping in *.cfg.xml specify which db the hbm belongs to via db attribute (default if not specified)
      // 3. CfgLoader generates hbmMap, where KEY=db name, and VALUE=hbm list
      // 4. Each db goes into seperate sessionFactory
      //======================================================================================


      // for each db instance in the configuration
      for(String instance : hbmMap.keySet() ) {

         try {
            if(session.get(instance) == null) {
               Configuration cfg = new Configuration();

               LOG.info("   : ---------- " + instance + " ----------");
         
               // load the hbmList
               for(String hbmFile : hbmMap.get(instance)) {
                  LOG.info("   : " + hbmFile);
                  cfg.addResource(hbmFile, mainClass);
               }

               // create session factory
               SessionFactory sf = cfg.configure("/" +instance+ ".db.xml").buildSessionFactory();
               sessionFactory.put(instance, sf);
               session.put(instance, new ThreadLocal<Session>());
           
            } else {
               LogFactory.getLog(HibernateUtil.class).info("Session [" +instance+ "] already initialized");
            }

         } catch (HibernateException ex) {
            LOG.error(ex);
            throw new RuntimeException("Configuration problem: " + ex.getMessage(), ex);
         }
      }
   }

   //--------------------------------------------------------------------------
   // this open the default session
   //--------------------------------------------------------------------------
   public static Session currentSession() throws HibernateException {
      return currentSession("default");
   }


   //--------------------------------------------------------------------------
   // this close default session
   //--------------------------------------------------------------------------
   public static void closeSession() throws HibernateException {
      closeSession("default");
   }


   //--------------------------------------------------------------------------
   // open session from named instance
   //--------------------------------------------------------------------------
   public static Session currentSession(String instance) throws HibernateException {
      Session s = (Session) session.get(instance).get();
      // Open a new Session, if this Thread has none yet
      if (s == null) {
         s = sessionFactory.get(instance).openSession();
         session.get(instance).set(s);
      }
      return s;
   }


   //--------------------------------------------------------------------------
   // close session from named instance
   //--------------------------------------------------------------------------
   public static void closeSession(String instance) throws HibernateException {
      Session s = (Session) session.get(instance).get();
      session.get(instance).set(null);
      if (s != null)
         s.close();
   }
}