用Java写一个雪花算法

雪花算法是一种生成分布式唯一ID的算法。下面是用Java实现的一个简单版本的雪花算法：

public class SnowflakeIdGenerator {
    private static final long EPOCH = 1288834974657L;
    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 ^ (-1L << WORKER_ID_BITS);
    private static final long MAX_DATA_CENTER_ID = -1L ^ (-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 ^ (-1L << SEQUENCE_BITS);
    private static long workerId = 1L;
    private static long dataCenterId = 1L;
    private static long sequence = 0L;
    private static long lastTimestamp = -1L;

    public static long generateId() {
        long timestamp = System.currentTimeMillis();
        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) & SEQUENCE_MASK;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }
        lastTimestamp = timestamp;
        return ((timestamp - EPOCH) << TIMESTAMP_LEFT_SHIFT) | (dataCenterId << DATA_CENTER_ID_SHIFT) | (workerId << WORKER_ID_SHIFT) | sequence;
    }

    private static long tilNextMillis(long lastTimestamp) {
        long timestamp = System.currentTimeMillis();
        while (timestamp <= lastTimestamp) {
            timestamp = System.currentTimeMillis();
        }
        return timestamp;
    }
}

使用方法：

long id = SnowflakeIdGenerator.generateId();

上面的代码实现了一个简单版本的雪花算法，用于生成64位的唯一ID。具体实现方法如下：

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