package twiter.snowflake;
/**
* twitter的snowflake算法 -- java實現
*/
public class SnowFlake {
/**
* 起始的時間戳
*/
private final static long START_STMP = 1480166465631L;
/**
* 每一部分佔用的位數
*/
//序列號佔用的位數
private final static long SEQUENCE_BIT = 12;
//機器標識佔用的位數
private final static long MACHINE_BIT = 5;
//數據中心佔用的位數
private final static long DATACENTER_BIT = 5;
/**
* 每一部分的最大值
*/
private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);
/**
* 每一部分向左的位移
*/
private final static long MACHINE_LEFT = SEQUENCE_BIT;
private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;
private long datacenterId;
private long machineId;
/**
* 序列號
*/
private long sequence = 0L;
/**
* 上一次時間戳
*/
private long lastStmp = -1L;
/**
* 構造器
*
* @param datacenterId 數據中心id (32之內,0~31)
* @param machineId 機器標識id (32之內,0~31)
*/
public SnowFlake(long datacenterId, long machineId) {
if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
}
if (machineId > MAX_MACHINE_NUM || machineId < 0) {
throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
}
/*if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
datacenterId = datacenterId & (MAX_DATACENTER_NUM - 1);
}
if (machineId > MAX_MACHINE_NUM || machineId < 0) {
machineId = machineId & (MAX_MACHINE_NUM - 1);
}*/
this.datacenterId = datacenterId;
this.machineId = machineId;
this.lastStmp = System.currentTimeMillis();
}
/**
* 產生下一個ID
*
* @return
*/
public synchronized long nextId() {
long currStmp = getNewstmp();
if (currStmp < lastStmp) {
throw new RuntimeException("Clock moved backwards. Refusing to generate id");
}
if (currStmp == lastStmp) {
//相同毫秒內,序列號自增
sequence = (sequence + 1) & MAX_SEQUENCE;
//同一毫秒的序列數已經達到最大
if (sequence == 0L) {
currStmp = getNextMill();
}
} else {
//不同毫秒內,序列號置爲0
sequence = 0L;
}
lastStmp = currStmp;
return (currStmp - START_STMP) << TIMESTMP_LEFT //時間戳部分
| datacenterId << DATACENTER_LEFT //數據中心部分
| machineId << MACHINE_LEFT //機器標識部分
| sequence; //序列號部分
}
private long getNextMill() {
long mill = getNewstmp();
while (mill <= lastStmp) {
mill = getNewstmp();
}
return mill;
}
private long getNewstmp() {
return System.currentTimeMillis();
}
public static void main(String[] args) {
/**
* datacenterId 數據中心id
* machineId 機器標識id
*/
long datacenterId = 1L;
long machineId = 4L;
SnowFlake snowFlake = new SnowFlake(datacenterId, machineId);
for (int i = 0; i < (1 << 10); i++) {
System.out.println(snowFlake.nextId());
}
}
}
推特雪花算法 java實現 原
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