code: @Override
      public void begin() throws NotSupportedException, SystemException
      {
          if (log.isDebugEnabled())
              log.info("beginning JTA transaction");
  
          Transaction tx = threadLocal.get();
          if (tx != null)
          {
              if ((tx.getStatus() == Status.STATUS_MARKED_ROLLBACK))
              {
                  throw new NotSupportedException("Nested Transaction not supported!");
              }
          }
  
          Integer timer = timerThead.get();
          threadLocal.set(new KunderaTransaction(timer != null ? timer : DEFAULT_TIME_OUT));
      }
docs: /*
  (non-Javadoc)
  
  @see javax.transaction.UserTransaction#begin()