keyedCallbacks = null;
   public void rollback() throws Exception   {      if (trace) { log.trace("executing before rollback hooks " + this); }            boolean onePhase = state != STATE_PREPARED;            Iterator iter = callbacks.iterator();            while (iter.hasNext())      {         TxCallback callback = (TxCallback)iter.next();                  callback.beforeRollback(onePhase);      }            state = STATE_ROLLEDBACK;            if (trace) { log.trace("rolled back " + this); }            iter = callbacks.iterator();            if (trace) { log.trace("executing after prepare hooks " + this); }            while (iter.hasNext())      {         TxCallback callback = (TxCallback)iter.next();                  callback.afterRollback(onePhase);      }                        callbacks = null;            keyedCallbackMap = null;            if (trace) { log.trace("rollback process complete " + this); }   }