java雪花算法生成主键id

Java中的雪花算法（Snowflake）可以用于生成唯一的主键ID。下面是一个简单的实现示例：

public class SnowflakeIdGenerator {
    private final static long START_TIMESTAMP = 1614556800000L; // 设置起始时间戳，这里假设为2021-03-01 00:00:00
    private final static long DATA_CENTER_ID_BITS = 5L; // 数据中心ID所占的位数
    private final static long WORKER_ID_BITS = 5L; // 工作机器ID所占的位数
    private final static long SEQUENCE_BITS = 12L; // 序列号所占的位数

    private final static long MAX_DATA_CENTER_ID = ~(-1L << DATA_CENTER_ID_BITS); // 支持的最大数据中心ID数量
    private final static long MAX_WORKER_ID = ~(-1L << WORKER_ID_BITS); // 支持的最大工作机器ID数量

    private final static long WORKER_ID_SHIFT = SEQUENCE_BITS; // 工作机器ID左移位数
    private final static long DATA_CENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS; // 数据中心ID左移位数
    private final static long TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATA_CENTER_ID_BITS; // 时间戳左移位数
    private final static long SEQUENCE_MASK = ~(-1L << SEQUENCE_BITS); // 序列号掩码

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

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

    public synchronized long generateId() {
        long currentTimestamp = System.currentTimeMillis();
        if (currentTimestamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards. Refusing to generate ID for " + (lastTimestamp - currentTimestamp) + " milliseconds");
        }

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

        lastTimestamp = currentTimestamp;

        return ((currentTimestamp - START_TIMESTAMP) << TIMESTAMP_LEFT_SHIFT)
                | (dataCenterId << DATA_CENTER_ID_SHIFT)
                | (workerId << WORKER_ID_SHIFT)
                | sequence;
    }

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

使用示例：

public class Main {
    public static void main(String[] args) {
        // 创建一个SnowflakeIdGenerator实例，传入数据中心ID和工作机器ID
        SnowflakeIdGenerator idGenerator = new SnowflakeIdGenerator(1, 1);

        // 生成ID
        long id = idGenerator.generateId();
        System.out.println("Generated ID: " + id);
    }
}

这样就可以使用雪花算法在Java中生成唯一的主键ID了。