package com.gkhy.safePlatform.commons.utils.idService;
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public class IdGenerateUtil {
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// 起始的时间戳
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private final static long START_STMP = 1577808000000L; //2020-01-01
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// 每一部分占用的位数，就三个
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private final static long SEQUENCE_BIT = 10; //序列号占用的位数
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private final static long TABLE_BIT = 7; //数据库表占用的位数
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private final static long BIZ_BIT = 5; //业务占用的位数
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// 每一部分最大值
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private final static long MAX_BIZ_NUM = -1L ^ (-1L << BIZ_BIT);
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private final static long MAX_TABLE_NUM = -1L ^ (-1L << TABLE_BIT);
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private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);
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// 每一部分向左的位移
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private final static long MACHINE_LEFT = SEQUENCE_BIT;
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private final static long DATACENTER_LEFT = SEQUENCE_BIT + TABLE_BIT;
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private final static long TIMESTMP_LEFT = DATACENTER_LEFT + BIZ_BIT;
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private long bizId; //业务标识
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private long tableId; //数据库表标识
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private long sequence = 0L; //序列号
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private long lastStmp = -1L; //上一次时间戳
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public IdGenerateUtil() {
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}
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// public SnowFlakeUtil(long bizId, long tableId) {
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// if (bizId > MAX_BIZ_NUM || bizId < 0) {
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// throw new IllegalArgumentException("bizId can't be greater than MAX_BIZ_NUM or less than 0");
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// }
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// if (tableId > MAX_TABLE_NUM || tableId < 0) {
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// throw new IllegalArgumentException("tableId can't be greater than MAX_TABLE_NUM or less than 0");
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// }
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// this.bizId = bizId;
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// this.tableId = tableId;
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// }
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public synchronized long nextId(long bizId, long tableId) {
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if (bizId > MAX_BIZ_NUM || bizId < 0) {
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throw new IllegalArgumentException("bizId can't be greater than MAX_BIZ_NUM or less than 0");
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}
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if (tableId > MAX_TABLE_NUM || tableId < 0) {
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throw new IllegalArgumentException("tableId can't be greater than MAX_TABLE_NUM or less than 0");
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}
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long currStmp = timeGen();
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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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if (currStmp == lastStmp) {
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//if条件里表示当前调用和上一次调用落在了相同毫秒内，只能通过第三部分，序列号自增来判断为唯一，所以+1.
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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，只能等待下一个毫秒
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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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//执行到这个分支的前提是currTimestamp > lastTimestamp，说明本次调用跟上次调用对比，已经不再同一个毫秒内了，这个时候序号可以重新回置0了。
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sequence = 0L;
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}
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lastStmp = currStmp;
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//就是用相对毫秒数、机器ID和自增序号拼接
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return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
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| bizId << DATACENTER_LEFT //业务部分
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| tableId << MACHINE_LEFT //数据库表部分
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| sequence; //序列号部分
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}
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//产生下一个ID
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public synchronized long nextId() {
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long currStmp = timeGen();
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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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if (currStmp == lastStmp) {
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//if条件里表示当前调用和上一次调用落在了相同毫秒内，只能通过第三部分，序列号自增来判断为唯一，所以+1.
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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，只能等待下一个毫秒
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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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//执行到这个分支的前提是currTimestamp > lastTimestamp，说明本次调用跟上次调用对比，已经不再同一个毫秒内了，这个时候序号可以重新回置0了。
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sequence = 0L;
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}
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lastStmp = currStmp;
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//就是用相对毫秒数、机器ID和自增序号拼接
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return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
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| bizId << DATACENTER_LEFT //业务部分
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| tableId << MACHINE_LEFT //数据库表部分
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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 = timeGen();
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while (mill <= lastStmp) {
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mill = timeGen();
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}
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return mill;
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}
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private long timeGen() {
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return System.currentTimeMillis();
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}
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/* // 测试
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public static void main(String[] args) {
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SnowFlake snowFlow = new SnowFlake(1, 1);
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// for (int i = 0; i < 3; i++) {
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// System.out.println(snowFlow.nextId());
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// }
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System.out.println(snowFlow.nextId());
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}*/
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}
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