java 版的雪花算法

您好，以下是 Java 版的雪花算法实现：

public class Snowflake {
    // 机器ID占用的位数
    private static final long MACHINE_BIT = 5L;
    // 数据中心ID占用的位数
    private static final long DATA_CENTER_BIT = 5L;
    // 序列号占用的位数
    private static final long SEQUENCE_BIT = 12L;

    // 最大的机器ID和数据中心ID
    private static final long MAX_MACHINE_ID = ~(-1L << MACHINE_BIT);
    private static final long MAX_DATA_CENTER_ID = ~(-1L << DATA_CENTER_BIT);

    private static final long EPOCH = 1483200000000L;

    private long machineId;
    private long dataCenterId;
    private long sequence = 0L;
    private long lastTimestamp = -1L;

    public Snowflake(long machineId, long dataCenterId) {
        if (machineId > MAX_MACHINE_ID || machineId < 0) {
            throw new IllegalArgumentException("Machine ID can't be greater than "
                    + MAX_MACHINE_ID + " or less than 0!");
        }
        if (dataCenterId > MAX_DATA_CENTER_ID || dataCenterId < 0) {
            throw new IllegalArgumentException("Datacenter ID can't be greater than "
                    + MAX_DATA_CENTER_ID + " or less than 0!");
        }
        this.machineId = machineId;
        this.dataCenterId = dataCenterId;
    }

    public synchronized long nextId() {
        long currentTimestamp = System.currentTimeMillis();
        if (currentTimestamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards. Refusing to generate id.");
        }
        if (currentTimestamp == lastTimestamp) {
            sequence = (sequence + 1) & ~(-1L << SEQUENCE_BIT);
            if (sequence == 0L) {
                currentTimestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }
        lastTimestamp = currentTimestamp;
        return (currentTimestamp - EPOCH) << (MACHINE_BIT + DATA_CENTER_BIT + SEQUENCE_BIT)
                | dataCenterId << (MACHINE_BIT + SEQUENCE_BIT)
                | machineId << SEQUENCE_BIT
                | sequence;
    }

    private long tilNextMillis(long lastTimestamp) {
        long timestamp = System.currentTimeMillis();
        while (timestamp <= lastTimestamp) {
            timestamp = System.currentTimeMillis();
        }
        return timestamp;
    }
}

希望能对您有所帮助。