java 雪花算法生成数字id

你可以使用Java编写雪花算法来生成数字ID。雪花算法是一种分布式唯一ID生成算法，它可以在多台机器上生成不重复的ID。

以下是一个简单的Java实现示例：

public class SnowflakeIdGenerator {
    private final long epoch = 1609459200000L;  // 设置起始时间戳，例如：2021-01-01 00:00:00
    private final long workerIdBits = 5L;       // 机器ID所占的位数
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);  // 最大机器ID
    private final long sequenceBits = 12L;      // 序列号所占的位数
    private final long workerIdShift = sequenceBits;  // 机器ID向左移的位数
    private final long timestampShift = sequenceBits + workerIdBits;  // 时间戳向左移的位数
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);  // 序列号的掩码

    private long workerId;
    private long sequence = 0L;
    private long lastTimestamp = -1L;

    public SnowflakeIdGenerator(long workerId) {
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException("Worker ID超出范围");
        }
        this.workerId = workerId;
    }

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

        if (timestamp < lastTimestamp) {
            throw new RuntimeException("时钟回拨异常");
        }

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

        lastTimestamp = timestamp;

        return ((timestamp - epoch) << timestampShift)
                | (workerId << workerIdShift)
                | 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) {
        SnowflakeIdGenerator idGenerator = new SnowflakeIdGenerator(1);
        long id = idGenerator.generateId();
        System.out.println(id);
    }
}

在上面的示例中，SnowflakeIdGenerator类接受一个workerId作为参数，用于标识不同的机器。generateId()方法会生成一个唯一的数字ID。你可以根据自己的需求进行调整和扩展。