分布式ID生成

最新推荐文章于 2025-05-26 15:12:33 发布

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本文介绍了Java实现的IdWorker类，用于生成带有时间戳的全局唯一ID，关注了并发控制、时间戳处理和机器标识符的管理。通过实例方法和私有辅助函数，确保了ID的生成既高效又正确。

public class IdWorker {
    private final static Logger logger = LoggerFactory.getLogger(IdWorker.class);

    private final long workerId;
    private final long epoch = 1403854494756L;   // 时间起始标记点，作为基准，一般取系统的最近时间
    private final long workerIdBits = 10L;      // 机器标识位数
    private final long maxWorkerId = -1L ^ -1L << this.workerIdBits;// 机器ID最大值: 1023
    private long sequence = 0L;                   // 0，并发控制
    private final long sequenceBits = 12L;      //毫秒内自增位

    private final long workerIdShift = this.sequenceBits;                             // 12
    private final long timestampLeftShift = this.sequenceBits + this.workerIdBits;// 22
    private final long sequenceMask = -1L ^ -1L << this.sequenceBits;                 // 4095,111111111111,12位
    private long lastTimestamp = -1L;

    private IdWorker(long workerId) {
        System.out.println("workerId:"+workerId);
        if (workerId > this.maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", this.maxWorkerId));
        }
        this.workerId = workerId;
    }

    public synchronized long nextId() throws Exception {
        long timestamp = timeGen();
        if (this.lastTimestamp == timestamp) { // 如果上一个timestamp与新产生的相等，则sequence加一(0-4095循环); 对新的timestamp，sequence从0开始
            this.sequence = this.sequence + 1 & this.sequenceMask;
            if (this.sequence == 0) {
                timestamp = this.tilNextMillis(this.lastTimestamp);// 重新生成timestamp
            }
        } else {
            this.sequence = 0;
        }

        if (timestamp < this.lastTimestamp) {
            logger.error(String.format("clock moved backwards.Refusing to generate id for %d milliseconds", (this.lastTimestamp - timestamp)));
            throw new Exception(String.format("clock moved backwards.Refusing to generate id for %d milliseconds", (this.lastTimestamp - timestamp)));
        }

        this.lastTimestamp = timestamp;
        return timestamp - this.epoch << this.timestampLeftShift | this.workerId << this.workerIdShift | this.sequence;
    }

    private static IdWorker instance;

    public static IdWorker getFlowIdWorkerInstance() {
        if (instance == null) {
            synchronized (IdWorker.class) {
                if (instance == null) {
                    instance = new IdWorker(workerIp());
                }
            }
        }
        return instance;
    }


    /**
     * 等待下一个毫秒的到来, 保证返回的毫秒数在参数lastTimestamp之后
     */
    private long tilNextMillis(long lastTimestamp) {
        long timestamp = this.timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = this.timeGen();
        }
        return timestamp;
    }

    /**
     * 获得系统当前毫秒数
     */
    private static long timeGen() {
        return System.currentTimeMillis();
    }

    public static Long workerIp() {
        String ipString = IPUtils.getInternalIp();
        Long[] ip = new Long[4];
        int pos1= ipString.indexOf(".");
        int pos2= ipString.indexOf(".",pos1+1);
        int pos3= ipString.indexOf(".",pos2+1);
        ip[3] = Long.parseLong(ipString.substring(pos3+1));
        return ip[3];
    }


}