package com.javaweb.common.utils;
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import java.util.Random;
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public class IdWorker {
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private final static long twepoch = 1288834974657L;
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// 机器标识位数
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private final static long workerIdBits = 5L;
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// 数据中心标识位数
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private final static long datacenterIdBits = 5L;
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// 机器ID最大值
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private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
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// 数据中心ID最大值
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private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
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// 毫秒内自增位
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private final static long sequenceBits = 12L;
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// 机器ID偏左移12位
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private final static long workerIdShift = sequenceBits;
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// 数据中心ID左移17位
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private final static long datacenterIdShift = sequenceBits + workerIdBits;
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// 时间毫秒左移22位
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private final static long timestampLeftShift = sequenceBits + workerIdBits
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+ datacenterIdBits;
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private final static long sequenceMask = -1L ^ (-1L << sequenceBits);
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private static long lastTimestamp = -1L;
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private long sequence = 0L;
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private final long workerId;
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private final long datacenterId;
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public IdWorker(long workerId, long datacenterId) {
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if (workerId > maxWorkerId || workerId < 0) {
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if (workerId == -1){
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this.workerId = new Random().nextInt((int)maxWorkerId);
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}else{
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throw new IllegalArgumentException(
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"worker Id can't be greater than %d or less than 0");
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}
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}else{
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this.workerId = workerId;
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}
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if (datacenterId > maxDatacenterId || datacenterId < 0) {
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if (datacenterId == -1){
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this.datacenterId = new Random().nextInt((int)maxDatacenterId);
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}else{
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throw new IllegalArgumentException(
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"datacenter Id can't be greater than %d or less than 0");
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}
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}else{
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this.datacenterId = datacenterId;
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}
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}
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public synchronized long nextId() {
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long timestamp = timeGen();
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if (timestamp < lastTimestamp) {
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try {
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throw new Exception(
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"Clock moved backwards. Refusing to generate id for "
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+ (lastTimestamp - timestamp) + " milliseconds");
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} catch (Exception e) {
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e.printStackTrace();
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}
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}
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if (lastTimestamp == timestamp) {
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// 当前毫秒内，则+1
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sequence = (sequence + 1) & sequenceMask;
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if (sequence == 0) {
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// 当前毫秒内计数满了，则等待下一秒
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timestamp = tilNextMillis(lastTimestamp);
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}
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} else {
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sequence = 0;
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}
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lastTimestamp = timestamp;
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// ID偏移组合生成最终的ID，并返回ID
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long nextId = ((timestamp - twepoch) << timestampLeftShift)
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| (datacenterId << datacenterIdShift)
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| (workerId << workerIdShift) | sequence;
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return nextId;
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}
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private long tilNextMillis(final long lastTimestamp) {
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long timestamp = this.timeGen();
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while (timestamp <= lastTimestamp) {
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timestamp = this.timeGen();
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}
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return timestamp;
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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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// //////////// test ////////////
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//
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// public static void main(String[] args) throws Exception {
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// final Set<Long> set = SetUtils.newHashSet();
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//
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// final IdWorker w1 = new IdWorker(-1, -1);
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// final IdWorker w2 = new IdWorker(-1, -1);
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// final CyclicBarrier cdl = new CyclicBarrier(100);
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//
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// for (int i = 0; i < 1000; i++) {
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// new Thread(new Runnable() {
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// @Override
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// public void run() {
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// try {
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// cdl.await();
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// } catch (InterruptedException e) {
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// e.printStackTrace();
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// } catch (BrokenBarrierException e) {
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// e.printStackTrace();
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// }
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//
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// // id
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// Long id = w1.nextId();
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// if (set.contains(id)){
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// System.out.println(id + " exists");
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// }
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// set.add(id);
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// System.out.println(id);
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//
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// // id2
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// Long id2 = w2.nextId();
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// if (set.contains(id2)){
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// System.out.println(id2 + " exists");
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// }
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// set.add(id2);
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// System.out.println(id2);
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// }
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// }).start();
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// }
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// try {
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// TimeUnit.SECONDS.sleep(5);
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// } catch (InterruptedException e) {
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// e.printStackTrace();
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// }
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// }
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}
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