update at 2021-07-16 09:37:58 by ehlxr
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3947896a04
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/*
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* The MIT License (MIT)
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*
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* Copyright © 2021 xrv <xrg@live.com>
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package io.github.ehlxr;
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import java.time.LocalTime;
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import java.util.LinkedList;
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import java.util.List;
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import java.util.Map;
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import java.util.Random;
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import java.util.concurrent.ConcurrentHashMap;
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/**
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* 滑动时间窗口限流工具
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* 本限流工具只适用于单机版，如果想要做全局限流，可以按本程序的思想，用redis的List结构去实现
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*
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* @author dijia478
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* @date 2020-10-13 10:53
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*/
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public class SlideWindow {
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/**
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* 队列id和队列的映射关系，队列里面存储的是每一次通过时候的时间戳，这样可以使得程序里有多个限流队列
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*/
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private volatile static Map<String, List<Long>> MAP = new ConcurrentHashMap<>();
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private SlideWindow() {
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}
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public static void main(String[] args) throws InterruptedException {
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while (true) {
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// 任意10秒内，只允许2次通过
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System.out.println(LocalTime.now().toString() + SlideWindow.isGo("ListId", 5, 1000L));
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// 睡眠0-10秒
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// Thread.sleep(1000 * new Random().nextInt(10));
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}
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}
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/**
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* 滑动时间窗口限流算法
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* 在指定时间窗口，指定限制次数内，是否允许通过
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*
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* @param listId 队列id
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* @param count 限制次数
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* @param timeWindow 时间窗口大小
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* @return 是否允许通过
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*/
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public static synchronized boolean isGo(String listId, int count, long timeWindow) {
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// 获取当前时间
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long nowTime = System.currentTimeMillis();
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// 根据队列id，取出对应的限流队列，若没有则创建
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List<Long> list = MAP.computeIfAbsent(listId, k -> new LinkedList<>());
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// 如果队列还没满，则允许通过，并添加当前时间戳到队列开始位置
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if (list.size() < count) {
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list.add(0, nowTime);
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return true;
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}
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// 队列已满（达到限制次数），则获取队列中最早添加的时间戳
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Long farTime = list.get(count - 1);
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// 用当前时间戳 减去 最早添加的时间戳
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if (nowTime - farTime <= timeWindow) {
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// 若结果小于等于timeWindow，则说明在timeWindow内，通过的次数大于count
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// 不允许通过
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return false;
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} else {
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// 若结果大于timeWindow，则说明在timeWindow内，通过的次数小于等于count
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// 允许通过，并删除最早添加的时间戳，将当前时间添加到队列开始位置
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list.remove(count - 1);
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list.add(0, nowTime);
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return true;
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}
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}
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}
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