【Java工具五】java获取系统订单号方法

拼搏现实的明天。 2022-05-18 04:51 330阅读 0赞

public class IdGen {
        private long workerId;
        private long datacenterId;
        private long sequence = 0L;
        private long twepoch = 1288834974657L; //Thu, 04 Nov 2010 01:42:54 GMT
        private long workerIdBits = 0L; //节点ID长度
        private long datacenterIdBits = 1L; //数据中心ID长度
        private long maxWorkerId = -1L ^ (-1L << workerIdBits); //最大支持机器节点数0~31，一共32个
        private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits); //最大支持数据中心节点数0~31，一共32个
        private long sequenceBits = 1L; //序列号12位
        private long workerIdShift = sequenceBits; //机器节点左移12位
        private long datacenterIdShift = sequenceBits + workerIdBits; //数据中心节点左移17位
        private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits; //时间毫秒数左移22位
        private long sequenceMask = -1L ^ (-1L << sequenceBits); //4095
        private long lastTimestamp = -1L;
        private static class IdGenHolder {
            private static final IdGen instance = new IdGen();
        }
        public static IdGen get(){
            return IdGenHolder.instance;
        }
        public IdGen() {
            this(0L, 0L);
        }
        public IdGen(long workerId, long datacenterId) {
            if (workerId > maxWorkerId || workerId < 0) {
                throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
            }
            if (datacenterId > maxDatacenterId || datacenterId < 0) {
                throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
            }
            this.workerId = workerId;
            this.datacenterId = datacenterId;
        }
        public synchronized long nextId() {
            long timestamp = timeGen(); //获取当前毫秒数
            //如果服务器时间有问题(时钟后退) 报错。
            if (timestamp < lastTimestamp) {
                throw new RuntimeException(String.format(
                        "Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
            }
            //如果上次生成时间和当前时间相同,在同一毫秒内
            if (lastTimestamp == timestamp) {
                //sequence自增，因为sequence只有12bit，所以和sequenceMask相与一下，去掉高位
                sequence = (sequence + 1) & sequenceMask;
                //判断是否溢出,也就是每毫秒内超过4095，当为4096时，与sequenceMask相与，sequence就等于0
                if (sequence == 0) {
                    timestamp = tilNextMillis(lastTimestamp); //自旋等待到下一毫秒
                }
            } else {
                sequence = 0L; //如果和上次生成时间不同,重置sequence，就是下一毫秒开始，sequence计数重新从0开始累加
            }
            lastTimestamp = timestamp;
            // 最后按照规则拼出ID。
            // 000000000000000000000000000000000000000000  00000            00000       000000000000
            // time                                                               datacenterId   workerId    sequence
            return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift)
                    | (workerId << workerIdShift) | sequence;
        }
        protected long tilNextMillis(long lastTimestamp) {
            long timestamp = timeGen();
            while (timestamp <= lastTimestamp) {
                timestamp = timeGen();
            }
            return timestamp;
        }
        protected long timeGen() {
            return System.currentTimeMillis();
        }
        
        public static void main(String[] args) {		
        	IdGen idGen = IdGen.get();
        	long nextId = idGen.nextId();
        	System.out.println(nextId);   	
    	}
    }