com.tianshouzhi.dragon.idgen.snowflake.IdGenSnowFlakeImpl Maven / Gradle / Ivy
package com.tianshouzhi.dragon.idgen.snowflake;
import com.tianshouzhi.dragon.idgen.AbstractIdGen;
/**
* Created by TIANSHOUZHI336 on 2017/3/9.
*/
public class IdGenSnowFlakeImpl extends AbstractIdGen {
/** 自定义元年 (2015-01-01),需要设置为一个固定值 */
public static final long DEFAULT_TWEPOCH =1420041600000L;
public static final int WORKER_ID_BITS =10;//默认最多可以扩容到1024台机器
public static final int SEQUENCE_BITS =12; /**最大sequenceId 4095*/
private long twepoch;
private int workerIdBits;
private int maxWorkerId;
private long workerId;
/**默认每毫秒最多可以产生4096个id*/
private int sequenceBits;
private long maxSequenceId;//
/** 毫秒内序列(0~4095) */
private long seqenceId = 0L;
/** 上次生成ID的时间截 */
private long lastTimestamp;
public IdGenSnowFlakeImpl(int workerId) {
this(DEFAULT_TWEPOCH, WORKER_ID_BITS, SEQUENCE_BITS,workerId);
}
public IdGenSnowFlakeImpl(long twepoch, int workerIdBits, int sequenceBits, int workerId) {
if(workerId<0||twepochmaxWorkerId){
throw new IllegalArgumentException("workerId("+workerId+")must <= maxWorkerId"+maxWorkerId);
}
this.sequenceBits = sequenceBits;
this.maxSequenceId=-1 ^ (-1 << sequenceBits);/** 生成序列的掩码，默认为4095 (0b111111111111=0xfff=4095) */
}
@Override
public synchronized Long getAutoIncrementId() throws Exception {
//如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退过这个时候应当抛出异常
long currentTimestamp = System.currentTimeMillis();
if (currentTimestamp < lastTimestamp) {
throw new RuntimeException(
String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - currentTimestamp));
}
if(currentTimestamp==lastTimestamp){
seqenceId=(seqenceId+1) & maxSequenceId;
if(seqenceId==0){
//阻塞到下一个毫秒,获得新的时间戳
currentTimestamp = tilNextMillis(lastTimestamp);
}
}else{
seqenceId = 0;//currentTime>lastTimestamp
}
//上次生成ID的时间截
lastTimestamp = currentTimestamp;
//移位并通过或运算拼到一起组成64位的ID
return ((currentTimestamp - DEFAULT_TWEPOCH) << ( WORKER_ID_BITS + SEQUENCE_BITS))
| (workerId << WORKER_ID_BITS)
| seqenceId;
}
/**
* 阻塞到下一个毫秒，直到获得新的时间戳
* @param lastTimestamp 上次生成ID的时间截
* @return 当前时间戳
*/
protected long tilNextMillis(long lastTimestamp) {
long timestamp = System.currentTimeMillis();
while (timestamp <= lastTimestamp) {
timestamp = System.currentTimeMillis();
}
return timestamp;
}
}