Java中的分布式ID生成策略：雪花算法与Snowflake

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省赚客开发者 2024-09-05 11:34:44 ©著作权

文章标签 Java 时间戳整型 文章分类 JavaScript 前端开发

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Java中的分布式ID生成策略：雪花算法与Snowflake

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在分布式系统中，生成全局唯一ID是一个常见需求。全局唯一ID用于确保在分布式环境中，每个事务或记录都能被唯一标识。雪花算法（Snowflake）是Twitter开源的一种分布式ID生成算法，它能够高效地生成唯一的64位长整型ID。本文将介绍雪花算法的原理，并展示如何在Java中实现和使用Snowflake算法。

雪花算法原理

雪花算法生成的ID是一个64位的长整型数，其结构如下：

1位符号位：0，正数。
41位时间戳：以毫秒为单位的时间戳，41位时间戳可以使用69年。
10位机器标识：可以部署在1024个节点，包括5位datacenterId和5位workerId。
12位序列号：支持同一毫秒内同一个节点可以生成4096个ID。

实现Snowflake算法

以下是使用Java实现Snowflake算法的示例代码：

package cn.juwatech.idworker;

public class SnowflakeIdWorker {
    private final long twepoch = 1288834974657L;
    private final long workerIdBits = 5L;
    private final long datacenterIdBits = 5L;
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    private final long sequenceBits = 12L;
    private final long workerIdShift = sequenceBits;
    private final long datacenterIdShift = sequenceBits + workerIdBits;
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);
    private long workerId;
    private long datacenterId;
    private long sequence = 0L;
    private long lastTimestamp = -1L;

    public SnowflakeIdWorker(long workerId, long datacenterId) {
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
        }
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }

    public synchronized long nextId() {
        long timestamp = timeGen();

        if (timestamp < lastTimestamp) {
            throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }

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

        lastTimestamp = timestamp;

        return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
    }

    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    protected long timeGen() {
        return System.currentTimeMillis();
    }

    public static void main(String[] args) {
        SnowflakeIdWorker idWorker = new SnowflakeIdWorker(0, 0);
        for (int i = 0; i < 1000; i++) {
            long id = idWorker.nextId();
            System.out.println(Long.toBinaryString(id));
            System.out.println(id);
        }
    }
}