用Java写一个32位序列id不重复

以下是一个基于Snowflake算法的Java代码实现，生成不重复的32位序列id：

public class IdGenerator {
    private static final long START_TIMESTAMP = 1480166465631L;
    private static final long WORKER_ID_BITS = 5L;
    private static final long DATA_CENTER_ID_BITS = 5L;
    private static final long MAX_WORKER_ID = ~(-1L << WORKER_ID_BITS);
    private static final long MAX_DATA_CENTER_ID = ~(-1L << DATA_CENTER_ID_BITS);
    private static final long SEQUENCE_BITS = 12L;
    private static final long WORKER_ID_SHIFT = SEQUENCE_BITS;
    private static final long DATA_CENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS;
    private static final long TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATA_CENTER_ID_BITS;
    private static final long SEQUENCE_MASK = ~(-1L << SEQUENCE_BITS);
    private static long lastTimestamp = -1L;
    private static long sequence = 0L;
    private final long workerId;
    private final long dataCenterId;

    public IdGenerator(long workerId, long dataCenterId) {
        if (workerId > MAX_WORKER_ID || workerId < 0) {
            throw new IllegalArgumentException("worker Id can't be greater than " + MAX_WORKER_ID + " or less than 0");
        }
        if (dataCenterId > MAX_DATA_CENTER_ID || dataCenterId < 0) {
            throw new IllegalArgumentException("datacenter Id can't be greater than " + MAX_DATA_CENTER_ID + " or less than 0");
        }
        this.workerId = workerId;
        this.dataCenterId = dataCenterId;
    }

    public synchronized long nextId() {
        long timestamp = timeGen();
        if (timestamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards. Refusing to generate id for " + (lastTimestamp - timestamp) + " milliseconds");
        }
        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & SEQUENCE_MASK;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }
        lastTimestamp = timestamp;
        return ((timestamp - START_TIMESTAMP) << TIMESTAMP_LEFT_SHIFT) |
                (dataCenterId << DATA_CENTER_ID_SHIFT) |
                (workerId << WORKER_ID_SHIFT) |
                sequence;
    }

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

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

使用方法如下：

IdGenerator idGenerator = new IdGenerator(1, 1); // 创建实例，传入workerId和dataCenterId
long id = idGenerator.nextId(); // 生成id

其中，workerId和dataCenterId可以根据具体业务需求进行分配。该代码实现中，workerId和dataCenterId均为5位，最大值为31，可以支持最多32个节点。同时，该算法的timestamp左移22位，可以支持到69年的时间戳