public class SnowflakeIdGenerator { // 起始的时间戳 (自定义纪元时间，通常为某个固定日期) private final long epoch = 1728571440L; // 这个时间戳是Twitter的纪元时间戳，可以自己定义 // 每个部分占用的位数 private final long workerIdBits = 5L; // 机器ID所占的位数 private final long datacenterIdBits = 5L; // 数据中心ID所占的位数 private final long sequenceBits = 12L; // 序列号所占的位数 // 最大值计算 private final long maxWorkerId = -1L ^ (-1L << workerIdBits); // 机器ID最大值 private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits); // 数据中心ID最大值 private final long maxSequence = -1L ^ (-1L << sequenceBits); // 序列号最大值 // 各部分左移的位数 private final long workerIdShift = sequenceBits; private final long datacenterIdShift = sequenceBits + workerIdBits; private final long timestampLeftShift = datacenterIdShift + datacenterIdBits; private final long sequenceMask = -1L ^ (-1L << sequenceBits); // 序列号掩码，用于序列号部分 private long workerId; // 机器ID private long datacenterId; // 数据中心ID private long sequence = 0L; // 序列号 private long lastTimestamp = -1L; // 上次生成ID的时间戳 // 构造函数，传入机器ID和数据中心ID public SnowflakeIdGenerator(long workerId, long datacenterId) { if (workerId > maxWorkerId || workerId < 0) { throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId)); } if (datacenterId > maxDatacenterId || datacenterId < 0) { throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId)); } this.workerId = workerId; this.datacenterId = datacenterId; } // 生成下一个ID public synchronized long nextId() { long timestamp = System.currentTimeMillis(); // 如果当前时间戳小于上次生成ID的时间戳，说明发生了时钟回拨 if (timestamp < lastTimestamp) { throw new RuntimeException("Clock moved backwards. Refusing to generate id for " + (lastTimestamp - timestamp) + " milliseconds"); } // 如果在同一毫秒内生成ID，序列号自增 if (timestamp == lastTimestamp) { sequence = (sequence + 1) & sequenceMask; if (sequence == 0) { // 如果序列号溢出，等待下一毫秒 timestamp = waitForNextMillis(lastTimestamp); } } else { // 如果时间戳不等于上次时间戳，说明进入了新的一毫秒，重置序列号 sequence = 0L; } lastTimestamp = timestamp; // 组合各部分，生成最终的ID return ((timestamp - epoch) << timestampLeftShift) // 时间戳部分 | (datacenterId << datacenterIdShift) // 数据中心ID部分 | (workerId << workerIdShift) // 机器ID部分 | sequence; // 序列号部分 } // 等待直到下一毫秒 private long waitForNextMillis(long lastTimestamp) { long timestamp = System.currentTimeMillis(); while (timestamp <= lastTimestamp) { timestamp = System.currentTimeMillis(); } return timestamp; } // 获取当前时间戳 public long currentTimestamp() { return System.currentTimeMillis(); } }