实现高性能分布式 ID 生成器：Java 雪花算法详解

public class SnowflakeIdGenerator {
    // 64位的时间偏移量
    private final static long TWEPOCH = 1288834974657L;
    // 机器id所占的位数
    private final static long WORKER_ID_BITS = 5L;
    // 数据标识id所占的位数
    private final static long DATA_CENTER_ID_BITS = 5L;
    // 序列在id中所占的位数
    private final static long SEQUENCE_BITS = 12L;
 
    // 机器ID最大值
    private final static long MAX_WORKER_ID = ~(-1L << WORKER_ID_BITS);
    // 数据标识id最大值
    private final static long MAX_DATA_CENTER_ID = ~(-1L << DATA_CENTER_ID_BITS);
 
    // 序列号的掩码，这里为4095 (0b111111111111=0xfff=4095)
    private final static long SEQUENCE_MASK = ~(-1L << SEQUENCE_BITS);
 
    // 工作机器ID(0~31)
    private long workerId;
    // 数据中心ID(0~31)
    private long dataCenterId;
    // 毫秒内序列(0~4095)
    private long sequence = 0L;
    // 上次生成ID的时间戳
    private long lastTimestamp = -1L;
 
    // 构造函数
    public SnowflakeIdGenerator(long workerId, long dataCenterId) {
        if (workerId > MAX_WORKER_ID || workerId < 0) {
            throw new IllegalArgumentException("worker Id can't be greater than %d or less than 0");
        }
        if (dataCenterId > MAX_DATA_CENTER_ID || dataCenterId < 0) {
            throw new IllegalArgumentException("dataCenter Id can't be greater than %d or less than 0");
        }
        this.workerId = workerId;
        this.dataCenterId = dataCenterId;
    }
 
    // 获得下一个ID
    public synchronized long nextId() {
        long timestamp = timeGen();
 
        // 如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退了，这是不允许的。
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(String.format(
                    "Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }
 
        // 如果是同一毫秒内重新生成ID，则进行序列号自增
        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & SEQUENCE_MASK;
            // 序列号溢出
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            // 如果是新的一毫秒，则序列号重置
            sequence = 0L;
        }
 
        // 记录最后一次生成ID的时间戳
        lastTimestamp = timestamp;
 
        // 移位并通过按位或运算生成ID
        return ((timestamp - TWEPOCH) << (DATA_CENTER_ID_BITS + WORKER_ID_BITS)) |
                (dataCenterId << WORKER_ID_BITS) |
                (workerId << SEQUENCE_BITS) |
                sequence;
    }
 
    // 获取当前时间戳