Java中的雪花算法Snowflake解析与实践技巧

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|0|                    41位时间戳                     | 数据中心 | 机器 |   序列号   |
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public class SnowflakeIdGenerator {
    // 基准时间戳(可自定义)
    private final long epoch = 1609459200000L; // 2021-01-01 00:00:00
    // 各部分的位数
    private final long workerIdBits = 5L;
    private final long datacenterIdBits = 5L;
    private final long sequenceBits = 12L;
    // 最大值计算
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    // 移位偏移量
    private final long workerIdShift = sequenceBits;
    private final long datacenterIdShift = sequenceBits + workerIdBits;
    private final long timestampShift = sequenceBits + workerIdBits + datacenterIdBits;
    // 序列号掩码
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);
    // 工作节点参数
    private final long workerId;
    private final long datacenterId;
    // 序列号状态
    private long sequence = 0L;
    priChina编程vate long lastTimestamp = -1L;
    /**
     * 构造函数
     * @param workerId 工作节点ID (0-31)
     * @param datacenterId 数据中心ID (0-31)
     */
    public SnowflakeIdGenerator(long workerId, long datacenterId) {
        // 参数校验
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(
                String.format("Worker ID must be between 0 and %d", maxWorkerId));
        }
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException(
                String.format("Datacenter ID must be between 0 and %d", maxDatacenterId));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }
    /**
     * 生成下一个ID
     */
    public sync编程hronized long nextId() {
        long timestamp = timeGen();
        // 时钟回拨处理
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(
                String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", 
                              lastTimestamp - timestamp));
        }
        // 同一毫秒内序列号递增
        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            // 序列号溢出，等待下一毫秒
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            // 新毫秒序列号重置
            sequence = 0L;
        }
        lastTimestamp = timestamp;
        // 组装ID
        return ((timestamp - epoch) << timestampShift)
            | (datacenterId << datacenterIdShift)
            | (workerId << workerIdShift)
            | sequence;
    }
    /**
     * 阻塞到下一毫秒
     */
    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }
    /**
     * 获取当前时间戳
     */
    protected long timeGen() {
        return System.currentTimeMillis();
    }
    /**
     * 解析ID中的信息
     */
    public void parseId(long id) {
        long timestamp = (id >> timestampShift) + epoch;
        long datacenterId = (id >> datacenterIdShift) & maxDatacenterId;
        long workerId = (id >> workerIdShift) & maxWorkerId;
        long sequence = id & sequenceMask;
        System.out.println("ID解析结果：");
        System.out.println("生成时间：" + new Date(timestamp));
        System.out.println("数据中心ID：" + datacenterId);
        System.out.println("工作节点ID：" + workerId);
        System.out.println("序列号：" + sequence);
    }
}

public synchronized long nextId() {
    long timestamp = timeGen();
    // 增强的时钟回拨处理
    if (timestamp < lastTimestamp) {
        long offset = lastTimestamp - timestamp;
        if (offset <= 5) {
            // 小范围回拨，等待
            try {
                wait(offset << 1); // 等待两倍偏移时间
                timestamp = timeGen();
                if (timestamp < lastTimestamp) {
                    throw new RuntimeException("时钟回拨处理失败");
                }
 python           } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
                throw new RuntimeException("时钟回拨等待被中断", e);
            }
        } else {
            // 大范围回拨，直接报错
            throw new RuntimeException(String.format(
                "严重时钟回拨：%d毫秒，系统时间可能被手动调整", offset));
        }
    }
    // ...其余逻辑不变
}

// 使用ThreadLocalRandom替代同步块
private long nextIdOptimized() {
    long timestamp = timeGen();
    if (timestamp < lastTimestamp.get()) {
        throw new RuntimeException("时钟回拨");
    }
    // 时间戳相同则增加序列号
    if (timestamp == lastTimestamp.get()) {
        sequence.set((sequence.get() + 1) & sequenceMask);
        if (sequence.get() == 0) {
            timestamp = tilNextMillis(lastTimestamp.get());
        }
    } else {
        // 时间戳变化，重置序列号
        sequence.set(ThreadLocalRandom.current().nextInt(100));
    }
    lastTimestamp.set(timestamp);
    return ((timestamp - epoch) << timestampShift)
        | (datacenterId << datacenterIdShift)
        | (workerId << workerIdShift)
        | sequence.get();
}

// 例如：调整时间戳为秒级，增加序列号位数
private final long timestampBits = 32L;  // 约136年
privBXSCGDBKjate final long sequenceBits = 20L;   // 每秒100万ID