Java雪花算法的实现详解

public class SnowflakeIdGenerator {
    // 起始的时间戳
    private final static long START_TIMESTAMP = 1609459200000L; // 2021-01-01 00:00:00

    // 每部分占用的位数
    private final static long SEQUENCE_BIT = 12; // 序列号占用的位数
    private final static long WORKER_BIT = 10; // 工作机器ID占用的位数
    private final static long TIMESTAMP_BIT = 41; // 时间戳占用的位数

    // 每部分的最大值
    private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);
    private final static long MAX_WORKER_ID = ~(-1L << WORKER_BIT);

    // 每部分向左的位移
    private final static long WORKER_LEFT = SEQUENCE_BIT;
    private final static long TIMESTAMP_LEFT = SEQUENCE_BIT + WORKER_BIT;

    private long workerId; // 工作机器ID
    private long sequence = 0L; // 序列号
    private long lastTimestamp = -1L; // 上次生成ID的时间戳

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

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

        if (timestamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards. Refusing to generate ID");
        }

        if (timestamp == lastTimestamp) {
            sequence = (sequence + 1) & MAX_SEQUENCE;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = timestamp;

        return ((timestamp - START_TIMESTAMP) << TIMESTAMP_LEFT)
                | (workerId << WORKER_LEFT)
                | sequence;
    }

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

public class Main {
    public static void main(String[] args) {
        SnowflakeIdGenerator idGenerator = new SnowflakeIdGenerator(1);
        long id = idGenerator.nextId();
        System.out.println("Generated ID: " + id);
    }
}