114 lines
3.5 KiB
Java
114 lines
3.5 KiB
Java
package com.sqx.config;
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/**
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* 描述: Twitter的分布式自增ID雪花算法snowflake (Java版)
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**/
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public class SnowFlake {
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/**
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* 起始的时间戳
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*/
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private final static long START_STMP = 1480166465631L;
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/**
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* 每一部分占用的位数
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*/
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private final static long SEQUENCE_BIT = 12; //序列号占用的位数
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private final static long MACHINE_BIT = 5; //机器标识占用的位数
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private final static long DATACENTER_BIT = 5;//数据中心占用的位数
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/**
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* 每一部分的最大值
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*/
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private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
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private final static long MAX_MACHINE_NUM = ~(-1L << MACHINE_BIT);
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private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BIT);
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/**
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* 每一部分向左的位移
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*/
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private final static long MACHINE_LEFT = SEQUENCE_BIT;
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private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
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private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;
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/**
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* 数据中心
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*/
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private long datacenterId;
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/**
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* 机器标识
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*/
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private long machineId;
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/**
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* 代表了一毫秒内生成的多个id的最新序号
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*/
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private long sequence = 10000L;
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/**
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* 上一次时间戳
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*/
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private long lastStmp = -1L;
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public SnowFlake() {
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}
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public SnowFlake(long datacenterId, long machineId) {
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if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
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throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
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}
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if (machineId > MAX_MACHINE_NUM || machineId < 0) {
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throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
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}
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this.datacenterId = datacenterId;
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this.machineId = machineId;
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}
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/**
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* 产生下一个ID
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*
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* @param ifEvenNum 是否偶数 true 时间不连续全是偶数 时间连续 奇数偶数 false 时间不连续 奇偶都有 所以一般建议用false
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*/
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public synchronized long nextId(boolean ifEvenNum) {
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long currStmp = getNewstmp();
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if (currStmp < lastStmp) {
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throw new RuntimeException("Clock moved backwards. Refusing to generate id");
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}
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/**
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* 时间不连续出来全是偶数
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*/
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if (ifEvenNum) {
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if (currStmp == lastStmp) {
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//相同毫秒内，序列号自增
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sequence = (sequence + 1) & MAX_SEQUENCE;
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//同一毫秒的序列数已经达到最大
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if (sequence == 0L) {
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currStmp = getNextMill();
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}
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} else {
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//不同毫秒内，序列号置为0
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sequence = 0L;
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}
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} else {
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//相同毫秒内，序列号自增
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sequence = (sequence + 1) & MAX_SEQUENCE;
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}
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lastStmp = currStmp;
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return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
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| datacenterId << DATACENTER_LEFT //数据中心部分
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| machineId << MACHINE_LEFT //机器标识部分
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| sequence; //序列号部分
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}
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private long getNextMill() {
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long mill = getNewstmp();
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while (mill <= lastStmp) {
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mill = getNewstmp();
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}
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return mill;
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}
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private long getNewstmp() {
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return System.currentTimeMillis();
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}
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} |