package twiter.snowflake;/*** twitter的snowflake算法 -- java实现*/
public class SnowFlake {/*** 起始的时间戳*/private final static long START_STMP = 1480166465631L;/*** 每一部分占用的位数*///序列号占用的位数private final static long SEQUENCE_BIT = 12;//机器标识占用的位数private final static long MACHINE_BIT = 5;//数据中心占用的位数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;/*** 序列号*/private long sequence = 0L;/*** 上一次时间戳*/private long lastStmp = -1L;/*** 构造器** @param datacenterId 数据中心id (32之内,0~31)* @param machineId    机器标识id (32之内,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();}/*** 产生下一个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) {currStmp = getNextMill();}} else {//不同毫秒内，序列号置为0sequence = 0L;}lastStmp = currStmp;return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分| datacenterId << DATACENTER_LEFT       //数据中心部分| machineId << MACHINE_LEFT             //机器标识部分| sequence;                             //序列号部分}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 数据中心id*  machineId    机器标识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());}}
}

算法思想