java 实现雪花算法

public class SnowflakeIdGenerator {
    
    
    private final static long START_TIMESTAMP = 1609528800000L;
     // 2021-01-01 00:00:00
    private final static long WORKER_ID_BITS = 5L;
    
    private final static long DATACENTER_ID_BITS = 5L;
    
    private final static long SEQUENCE_BITS = 12L;
    
    
    private final static long MAX_WORKER_ID = ~(-1L  WORKER_ID_BITS);
    
    private final static long MAX_DATACENTER_ID = ~(-1L  DATACENTER_ID_BITS);
    
    
    private final static long WORKER_ID_SHIFT = SEQUENCE_BITS;
    
    private final static long DATACENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS;
    
    private final static long TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATACENTER_ID_BITS;
    
    
    private final static long SEQUENCE_MASK = ~(-1L  SEQUENCE_BITS);
    
    
    private long workerId;
    
    private long datacenterId;
    
    private long sequence = 0L;
    
    private long lastTimestamp = -1L;

    
    public SnowflakeIdGenerator(long workerId, long datacenterId) {
    
        if (workerId >
 MAX_WORKER_ID || workerId  0) {
    
            throw new IllegalArgumentException("Worker ID can't be greater than " + MAX_WORKER_ID + " or less than 0");

        }
    
        if (datacenterId >
 MAX_DATACENTER_ID || datacenterId  0) {
    
            throw new IllegalArgumentException("Datacenter ID can't be greater than " + MAX_DATACENTER_ID + " or less than 0");

        }
    
        this.workerId = workerId;
    
        this.datacenterId = datacenterId;

    }

    
    public synchronized long nextId() {
    
        long timestamp = System.currentTimeMillis();

        if (timestamp  lastTimestamp) {
    
            throw new RuntimeException("Clock moved backwards. Refusing to generate id for " + (lastTimestamp - timestamp) + " milliseconds");

        }

        if (timestamp == lastTimestamp) {
    
            sequence = (sequence + 1) &
     SEQUENCE_MASK;

            if (sequence == 0L) {
    
                timestamp = tilNextMillis(lastTimestamp);

            }

        }
 else {
    
            sequence = 0L;

        }
    
        lastTimestamp = timestamp;
    
        
        return ((timestamp - START_TIMESTAMP)  TIMESTAMP_LEFT_SHIFT) |
            (datacenterId  DATACENTER_ID_SHIFT) |
            (workerId  WORKER_ID_SHIFT) |
            sequence;

    }

    
    private long tilNextMillis(long lastTimestamp) {
    
        long timestamp = System.currentTimeMillis();

        while (timestamp = lastTimestamp) {
    
            timestamp = System.currentTimeMillis();

        }
    
        return timestamp;

    }

}
    

使用方式:

java复制代码SnowflakeIdGeneratoridGenerator=newSnowflakeIdGenerator(workerId, datacenterId);
    
longid= idGenerator.nextId();
    

其中workerId和datacenterId是分别代表工作机器ID和数据中心ID，需要在不同的机器上设置不同的值。

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