基于时间随机数的流水号生成方案

public class IdGen {

    private final int len;

    private final int seqBit;

    private final int randomBit;

    private final int workBit;

    private final int workerId;

    private long lastTimestamp = 0L;

    private long sequence = 0L;

    private static final BigInteger UNIT = new BigInteger("10");

    private DateTimeFormatter FORMAT;

    /**
     *
     * @param len 长度 只能14, 17
     * @param seqBit 同一时间序号长度
     * @param randomBit 随机数长度用于混淆
     * @param workBit 机器号长度
     * @param workerId 机器号id
     */
    public IdGen(int len, int seqBit, int randomBit, int workBit , int workerId) {
        if ((len == 17)) {
            FORMAT = DateTimeFormatter.ofPattern("yyyyMMddHHmmssSSS");
        } else if ((len == 14)) {
            FORMAT = DateTimeFormatter.ofPattern("yyyyMMddHHmmss");
        } else {
            throw new IllegalArgumentException("时间长度只能为14或17");
        }

        this.workerId = workerId;
        this.seqBit = seqBit;
        this.workBit = workBit;
        this.randomBit = randomBit;
        this.len = len;
        int maxValue = (UNIT.pow(workBit).intValue() - 1);
        if (workerId > maxValue || workerId < 0) {
            throw new IllegalArgumentException(String.format("workerId不能大于[%d]，且不能小于0", maxValue));
        }
    }

    public synchronized String nextId() {
        long timestamp = now();

        if (timestamp < lastTimestamp) {
            throw new RuntimeException(String.format("时钟倒退[%s]ms", lastTimestamp - timestamp));
        }

        if (lastTimestamp == timestamp) {
            sequence = sequence + 1;
            // 当前毫秒内计数满了，则等待下一毫秒
            if (sequence >  (UNIT.pow(seqBit).intValue()-1)) {
                timestamp = nextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }
        lastTimestamp = timestamp;

        int random = ThreadLocalRandom.current().nextInt(0, UNIT.pow(randomBit).intValue());
        return String.format("%0"+len+"d", timestamp) +
                String.format("%0"+seqBit+"d", sequence) +
                String.format("%0"+randomBit+"d", random) +
                String.format("%0"+workBit+"d", workerId) ;
    }
    private long nextMillis(final long lastTimestamp) {
        long timestamp = this.now();
        while (timestamp <= lastTimestamp) {
            timestamp = this.now();
        }
        return timestamp;
    }

    private long now() {
        LocalDateTime dateTime = LocalDateTime.now();
        return Long.parseLong(dateTime.format(FORMAT));
    }

    public static void main(String[] args) {
        // 方案1
        IdGen gen1 = new IdGen(17, 3, 2,2, 1);
        System.out.println(gen1.nextId());
        // 方案2
        IdGen gen2 = new IdGen(14, 2, 2,1, 1);
        System.out.println(gen2.nextId());

        // 202304251014103330008201
        // 2023042510141000441

    }
}