if (log.isTraceEnabled()) { log.trace("installed listener " + listener); }
if (trace) { log.trace("installed listener " + listener); }
   public synchronized void setMessageListener(MessageListener listener) throws JMSException   {      // JMS consumer is single threaded, so it shouldn't be possible to set a MessageListener      // while another thread is receiving            if (receiverThread != null)      {         // Should never happen         throw new javax.jms.IllegalStateException("Another thread is already receiving");      }            this.listener = listener;      if (log.isTraceEnabled()) { log.trace("installed listener " + listener); }      activateConsumer();   }