分布式雪花算法

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 */
    private final static long SEQUENCE_BIT = 12; //序列号占用的位数
    private final static long MACHINE_BIT = 5;   //机器标识占用的位数
    private final static long DATACENTER_BIT = 5;//数据中心占用的位数

    /** * 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;  //数据中心
    private long machineId;     //机器标识
    private long sequence = 0L; //序列号
    private long lastStmp = -1L;//上一次时间戳

    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"); } this.datacenterId = datacenterId; this.machineId = machineId; } /** * 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 { //不一样毫秒内，序列号置为0
            sequence = 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) { SnowFlake snowFlake = new SnowFlake(1, 1); long start = System.currentTimeMillis(); for (int i = 0; i < 1000000; i++) { System.out.println(snowFlake.nextId()); } System.out.println(System.currentTimeMillis() - start); } }