java使用雪花算法生成id

雪花算法是Twitter开源的一种分布式ID生成算法，通过使用机器的MAC地址、时间戳、工作机器ID和自增序列来生成唯一的ID。Java实现雪花算法的代码如下：

public class SnowflakeIdWorker {
    // 起始的时间戳
    private final static long START_STMP = 1480166465631L;
    // 每一部分占用的位数
    private final static long SEQUENCE_BIT = 12; // 序列号占用的位数
    private final static long MACHINE_BIT = 5;   // 机器标识占用的位数
    private final static long DATACENTER_BIT = 5;// 数据中心占用的位数
    // 每一部分的最大值
    private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);
    // 每一部分向左的位移
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTAMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;
    private long datacenterId;  // 数据中心
    private long machineId;     // 机器标识
    private long sequence = 0L; // 序列号
    private long lastStmp = -1L;// 上一次时间戳

    public SnowflakeIdWorker(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    public synchronized long nextId() {
        long currStmp = getNewstmp();
        if (currStmp < lastStmp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }
        if (currStmp == lastStmp) {
            sequence = (sequence + 1) & MAX_SEQUENCE;
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {
            sequence = 0L;
        }
        lastStmp = currStmp;
        return (currStmp - START_STMP) << TIMESTAMP_LEFT // 时间戳部分
                | datacenterId << DATACENTER_LEFT       // 数据中心部分
                | machineId << MACHINE_LEFT             // 机器标识部分
                | sequence;                             // 序列号部分
    }

    private long getNextMill() {
        long mill = getNewstmp();
        while (mill <= lastStmp) {
            mill = getNewstmp();
        }
        return mill;
    }

    private long getNewstmp() {
        return System.currentTimeMillis();
    }
}

使用如下：

SnowflakeIdWorker idWorker = new SnowflakeIdWorker(0, 0);
long id = idWorker.nextId();
System.out.println(id);

其中参数datacenterId和machineId可以根据实际情况进行配置。