java高并发生成唯一编号

转载于 2024-07-26 03:03:05 发布 · 278 阅读

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Java高并发生成唯一编号

在互联网应用中，生成唯一编号是一个常见的需求，尤其是在高并发的场景下。Java提供了多种生成唯一编号的方法，本文将介绍其中一种基于Snowflake算法的实现方式，并展示如何使用Java代码实现。

什么是Snowflake算法？

Snowflake算法是一种分布式唯一ID生成算法，由Twitter公司开发。它通过一个64位的长整型数字来表示一个ID，其中包含时间戳、数据中心ID、机器ID和序列号。Snowflake算法的主要优点是生成的ID是唯一的，并且生成速度非常快。

Snowflake算法的实现

下面是一个使用Java实现Snowflake算法的示例代码：

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

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

    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 = 0;
        }

        lastTimestamp = timestamp;
        long diff = timestamp - twepoch;
        return (diff << timestampLeftShift) | (workerId << workerIdShift) | sequence;
    }

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

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