public class SnowFlakeUtils {
/**
* 起始时间戳，从2021-12-01开始生成
*/
private final static long START_STAMP = 1638288000000L;
/**
* 序列号占用的位数 12
*/
private final static long SEQUENCE_BIT = 12;
/**
* 机器标识占用的位数
*/
private final static long MACHINE_BIT = 10;
/**
* 机器数量最大值
*/
private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
/**
* 序列号最大值
*/
private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);
/**
* 每一部分向左的位移
*/
private final static long MACHINE_LEFT = SEQUENCE_BIT;
private final static long TIMESTAMP_LEFT = SEQUENCE_BIT + MACHINE_BIT;
/**
* 机器标识
*/
private final long machineId;
/**
* 序列号
*/
private long sequence = 0L;
/**
* 上一次时间戳
*/
private long lastStamp = -1L;
/**
* 构造方法
*
* @param machineId 机器ID
*/
public SnowFlakeUtils(long machineId) {
if (machineId > MAX_MACHINE_NUM || machineId < 0) {
throw new RuntimeException("机器超过最大数量");
}
this.machineId = machineId;
}
/**
* 产生下一个ID
*/
public synchronized long nextId() {
long currStamp = getNewStamp();
if (currStamp < lastStamp) {
throw new RuntimeException("时钟后移，拒绝生成ID！");
}
if (currStamp == lastStamp) {
// 相同毫秒内，序列号自增
sequence = (sequence + 1) & MAX_SEQUENCE;
// 同一毫秒的序列数已经达到最大
if (sequence == 0L) {
currStamp = getNextMill();
}
} else {
// 不同毫秒内，序列号置为0
sequence = 0L;
}
lastStamp = currStamp;
return (currStamp - START_STAMP) << TIMESTAMP_LEFT // 时间戳部分
| machineId << MACHINE_LEFT // 机器标识部分
| sequence; // 序列号部分
}
private long getNextMill() {
long mill = getNewStamp();
while (mill <= lastStamp) {
mill = getNewStamp();
}
return mill;
}
private long getNewStamp() {
return System.currentTimeMillis();
}
}
| 
