java实现雪花算法

雪花算法（Snowflake）是一种用于生成全局唯一ID的算法，常用于分布式系统中，主要包括时间戳、机器ID和序列号三个部分。下面是一个简单的Java实现雪花算法的示例代码：

public class Snowflake {
    private static final long START_TIMESTAMP = 1609459200000L; // 2021-01-01 00:00:00

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

    public Snowflake(long workerId) {
        this.workerId = workerId;
    }

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

        if (currentTimestamp < lastTimestamp) {
            throw new IllegalStateException("Invalid system clock");
        }

        if (currentTimestamp == lastTimestamp) {
            sequence = (sequence + 1) & 0x1FFF; // 0x1FFF = 8191
            if (sequence == 0) {
                currentTimestamp = waitNextMillis(currentTimestamp);
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = currentTimestamp;

        return ((currentTimestamp - START_TIMESTAMP) << 22) |
                (workerId << 12) |
                sequence;
    }

    private long waitNextMillis(long currentTimestamp) {
        long timestamp = System.currentTimeMillis();
        while (timestamp <= currentTimestamp) {
            timestamp = System.currentTimeMillis();
        }
        return timestamp;
    }
}

使用示例：

public class SnowflakeExample {
    public static void main(String[] args) {
        Snowflake snowflake = new Snowflake(1);

        for (int i = 0; i < 10; i++) {
            long id = snowflake.nextId();
            System.out.println(id);
        }
    }
}

在上述示例中，通过传入不同的workerId来区分不同的机器或节点，生成全局唯一的ID。请注意，这只是一个简单的实现示例，实际应用中需要根据具体情况进行调整和优化。