工具类总结(6)-订单生成工具类

浅浅的花香味﹌ 2022-06-05 12:40 234阅读 0赞

/** * 42位的时间前缀+10位的节点标识+12位的sequence避免并发的数字（12位不够用时强制得到新的时间前缀） * <p> * <b>对系统时间的依赖性非常强，需要关闭ntp的时间同步功能，或者当检测到ntp时间调整后，拒绝分配id。 * * @author sumory.wu * @date 2012-2-26 下午6:40:28 */
    public class IdWorker { 
    // private final static Logger logger = LoggerFactory.getLogger(IdWorker.class);
    
        private final long workerId;
        private final long snsEpoch = 1330328109047L;// 起始标记点，作为基准
        private long sequence = 0L;// 0，并发控制
        private final long workerIdBits = 10L;// 只允许workid的范围为：0-1023
        private final long maxWorkerId = -1L ^ -1L << this.workerIdBits;// 1023,1111111111,10位
        private final long sequenceBits = 12L;// sequence值控制在0-4095
    
        private final long workerIdShift = this.sequenceBits;// 12
        private final long timestampLeftShift = this.sequenceBits + this.workerIdBits;// 22
        private final long sequenceMask = -1L ^ -1L << this.sequenceBits;// 4095,111111111111,12位
    
        private long lastTimestamp = -1L;
    
        public IdWorker(long workerId) {
            super();
            if (workerId > this.maxWorkerId || workerId < 0) {
       // workid < 1024[10位：2的10次方]
                throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", this.maxWorkerId));
            }
            this.workerId = workerId;
        }
    
        public long nextId() throws Exception {
            long timestamp = this.timeGen();
            if (this.lastTimestamp == timestamp) {
       // 如果上一个timestamp与新产生的相等，则sequence加一(0-4095循环)，下次再使用时sequence是新值
                //System.out.println("lastTimeStamp:" + lastTimestamp);
                this.sequence = this.sequence + 1 & this.sequenceMask;
                if (this.sequence == 0) {
                    timestamp = this.tilNextMillis(this.lastTimestamp);// 重新生成timestamp
                }
            } else {
                this.sequence = 0;
            }
            if (timestamp < this.lastTimestamp) {
    // logger.error(String.format("Clock moved backwards.Refusing to generate id for %d milliseconds", (this.lastTimestamp - timestamp)));
                throw new Exception(String.format("Clock moved backwards.Refusing to generate id for %d milliseconds", (this.lastTimestamp - timestamp)));
            }
    
            this.lastTimestamp = timestamp;
            // 生成的timestamp
            return timestamp - this.snsEpoch << this.timestampLeftShift | this.workerId << this.workerIdShift | this.sequence;
        }
    
        /** * 保证返回的毫秒数在参数之后 * * @param lastTimestamp * @return */
        private long tilNextMillis(long lastTimestamp) {
            long timestamp = this.timeGen();
            while (timestamp <= lastTimestamp) {
                timestamp = this.timeGen();
            }
            return timestamp;
        }
    
        /** * 获得系统当前毫秒数 * * @return */
        private long timeGen() {
            return System.currentTimeMillis();
        }
    
        public static void main(String[] args) throws Exception {
            //IdWorker iw1 = new IdWorker(1);
            IdWorker iw2 = new IdWorker(2);
    // IdWorker iw3 = new IdWorker(3);
            long a = iw2.nextId();
            for (int i = 0; i < 100; i++)
                System.out.println(iw2.nextId());
    
        }
    }