此方法为何会生成相同的单号？

public synchronized long getDailyNextVal(String seqName, boolean needNew)
            throws BusinessException {
        long ret = 1L;
        int nowDay = Calendar.getInstance().get(Calendar.DATE);
        try {
            SequenceHome home = (SequenceHome)
                    ControlRepository.getInstance().getControlInstance(Names.SEQUENCE);
            Sequence seq = (Sequence) home.findByPrimaryKey(seqName);
            if (nowDay != seq.getDay()) {
                this.updateSequence(seq, seq.getStartby() + seq.getStep(), nowDay);
                return seq.getStartby();
            }
            ret = seq.getSequenceNo();
            this.updateSequence(seq, seq.getSequenceNo() + seq.getStep(), nowDay);
        } catch (BusinessException e) {
            if (needNew) {
//                createSequence(seqName, 1, 2, true);
                createSequence(seqName, 1, 1, true, nowDay);
            } else {
                log.error("sequence with name " + seqName + " not found", e);
                e.setDetailInfo("sequence with name " + seqName + " not found");
                throw e;
            }
        }
        return ret;
    }