Java限流代碼實現

常見的限流算法大致有三種：

令牌桶算法
漏桶算法
計數器算法

網上對令牌桶又細分爲固定窗口計數器限流和滑動窗口計數器限流，下面將對這幾種限流方式進行簡單的介紹及代碼實現。
注意：代碼中會考慮併發線程安全問題，非分佈式限流
Github地址：重構後的代碼

固定窗口計數器限流

固定窗口計數器限流就是在固定時間內（如10s），只允許固定的請求數訪問（如10個），超過的請求將受到限制。
實現邏輯圖

實現代碼

package com.dfy.ratelimiter.core;

import java.util.concurrent.TimeUnit;

/**
 * @description: 計數器限流
 * @author: DFY
 * @time: 2020/4/8 17:02
 */
public abstract class CounterLimit {

    /** 單位時間限制數 */
    protected int limitCount;
    /** 限制時間 */
    protected long limitTime;
    /** 時間單位，默認爲秒 */
    protected TimeUnit timeUnit;

    /** 當前是否爲受限狀態 */
    protected volatile boolean limited;

    /**
     * 嘗試將計數器加1，返回爲true表示能夠正常訪問接口，false表示訪問受限
     * @return
     */
    protected abstract boolean tryCount();
}

package com.dfy.ratelimiter.core;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.time.LocalDateTime;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * @description: 固定窗口計數器限流
 * @author: DFY
 * @time: 2020/4/8 15:50
 */
public class FixedWindowCounterLimit extends CounterLimit {

    private static Logger logger = LoggerFactory.getLogger(FixedWindowCounterLimit.class);

    /** 計數器 */
    private AtomicInteger counter = new AtomicInteger(0);

    public FixedWindowCounterLimit(int limitCount, long limitTime) {
        this(limitCount, limitTime, TimeUnit.SECONDS);
    }

    public FixedWindowCounterLimit(int limitCount, long limitTime, TimeUnit timeUnit) {
        this.limitCount = limitCount;
        this.limitTime = limitTime;
        this.timeUnit = timeUnit;
        new Thread(new CounterResetThread()).start(); // 開啓計數器清零線程
    }

    public boolean tryCount() {
        while (true) {
            if (limited) {
                return false;
            } else {
                int currentCount = counter.get();
                if (currentCount == limitCount) {
                    logger.info("限流：{}", LocalDateTime.now().toString());
                    limited = true;
                    return false;
                } else {
                    if (counter.compareAndSet(currentCount, currentCount + 1))
                        return true;
                }
            }
        }
    }

    class CounterResetThread implements Runnable {
        @Override
        public void run() {
            while (true) {
                try {
                    timeUnit.sleep(limitTime);
                    counter.compareAndSet(limitCount, 0); // 計數器清零
                    limited = false; // 修改當前狀態爲不受限
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

使用及測試
啓動項目，連續訪問接口，當在訪問第11次時接口受限，受限時間到後又能正常訪問。

private FixedWindowCounterLimit fixedWindowCounterLimit = new FixedWindowCounterLimit(10, 10);
@GetMapping("/hello")
public String hello() {
    if (!fixedWindowCounterLimit.tryCount()) {
        return "限流!";
    }
    return "hello world!";
}

存在的問題
限流不均勻，如下所示我們規定10S內至多10個訪問量，但2S內實際上有20個訪問量。

滑動窗口計數器限流

固定窗口計數器限流是在固定時間內訪問量受限，滑動窗口計數器限流是在滑動窗口內訪問量受限。
例子
如下是規定5S內不能超過10個訪問量，當已經達到10個訪問量，則訪問受限。使用該方式可以使受限均勻，任意連續的5S內都只能有10個訪問量。

實現代碼

package com.dfy.ratelimiter.core;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.time.LocalDateTime;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * @description: 滑動窗口計數器限流
 * @author: DFY
 * @time: 2020/4/8 17:01
 */
public class SlidingWindowCounterLimit extends CounterLimit {

    private static Logger logger = LoggerFactory.getLogger(SlidingWindowCounterLimit.class);

    /** 格子分佈 */
    private AtomicInteger[] gridDistribution;
    /** 當前時間在計數分佈的索引 */
    private volatile int currentIndex;
    /** 當前時間之前的滑動窗口計數 */
    private int preTotalCount;
    /** 格子數 */
    private int gridNumber;
    /** 是否正在執行狀態重置 */
    private volatile boolean resetting;

    public SlidingWindowCounterLimit(int gridNumber, int limitCount, long limitTime) {
        this(gridNumber, limitCount, limitTime, TimeUnit.SECONDS);
    }

    public SlidingWindowCounterLimit(int gridNumber, int limitCount, long limitTime, TimeUnit timeUnit) {
        if (gridNumber <= limitTime)
            throw new RuntimeException("無法完成限流，gridNumber必須大於limitTime，gridNumber = " + gridNumber + ",limitTime = " + limitTime);
        this.gridNumber = gridNumber;
        this.limitCount = limitCount;
        this.limitTime = limitTime;
        this.timeUnit = timeUnit;
        gridDistribution = new AtomicInteger[gridNumber];
        for (int i = 0; i < gridNumber; i++) {
            gridDistribution[i] = new AtomicInteger(0);
        }
        new Thread(new CounterResetThread()).start();
    }

    public boolean tryCount() {
        while (true) {
            if (limited) {
                return false;
            } else {
                int currentGridCount = gridDistribution[currentIndex].get();
                if (preTotalCount + currentGridCount == limitCount) {
                    logger.info("限流：{}", LocalDateTime.now().toString());
                    limited = true;
                    return false;
                }
                if (!resetting && gridDistribution[currentIndex].compareAndSet(currentGridCount, currentGridCount + 1))
                    return true;
            }
        }
    }

    class CounterResetThread implements Runnable {
        @Override
        public void run() {
            while (true) {
                try {
                    timeUnit.sleep(1); // 停止1個時間單位
                    int indexToReset = currentIndex - limitCount - 1; // 要重置計數的格子索引
                    if (indexToReset < 0) indexToReset += gridNumber;
                    resetting = true; // 防止在更新狀態時，用戶訪問接口將當前格子的訪問量 + 1
                    preTotalCount = preTotalCount - gridDistribution[indexToReset].get()
                            + gridDistribution[currentIndex++].get(); // 重置當前時間之前的滑動窗口計數
                    if (currentIndex == gridNumber) currentIndex = 0;
                    if (preTotalCount + gridDistribution[currentIndex].get() < limitCount)
                        limited = false; // 修改當前狀態爲不受限
                    resetting = false;
                    logger.info("當前格子：{}，重置格子：{}，重置格子訪問量：{}，前窗口格子總數：{}",
                            currentIndex, indexToReset, gridDistribution[indexToReset].get(), preTotalCount);
                    gridDistribution[indexToReset].set(0);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

使用及測試

private SlidingWindowCounterLimit slidingWindowCounterLimit = new SlidingWindowCounterLimit(20, 10, 10);
@GetMapping("/hello")
public String hello() {
    if (!slidingWindowCounterLimit.tryCount()) {
        return "限流!";
    }
    return "hello world!";
}

令牌桶限流

Google guava的RateLimiter提供了基於令牌桶算法的兩種實現，下面代碼只是簡單實現。

package com.dfy.ratelimiter.core;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.time.LocalDateTime;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * @description: 令牌桶限流
 * @author: DFY
 * @time: 2020/4/10 15:35
 */
public class TokenBucketLimit {

    private static Logger logger = LoggerFactory.getLogger(TokenBucketLimit.class);

    /** 給定時間生成令牌數 */
    private int genNumber;
    /** 生成令牌所花費的時間 */
    private int genTime;
    /** 時間單位，默認爲秒 */
    private TimeUnit timeUnit;
    /** 最大令牌數 */
    private int maxNumber;
    /** 已存儲的令牌數 */
    private AtomicInteger storedNumber;

    public TokenBucketLimit(int genNumber, int genTime, int maxNumber) {
        this(genNumber, genTime, TimeUnit.SECONDS, maxNumber);
    }

    public TokenBucketLimit(int genNumber, int genTime, TimeUnit timeUnit, int maxNumber) {
        this.genNumber = genNumber;
        this.genTime = genTime;
        this.timeUnit = timeUnit;
        this.maxNumber = maxNumber;
        this.storedNumber = new AtomicInteger(0);
        new Thread(new TokenGenerateThread()).start();
    }

    public boolean tryAcquire() {
        while (true) {
            int currentStoredNumber = storedNumber.get();
            if (currentStoredNumber == 0) {
                logger.info("限流：{}", LocalDateTime.now().toString());
                return false;
            }
            if (storedNumber.compareAndSet(currentStoredNumber, currentStoredNumber - 1)) {
                return true;
            }
        }
    }

    class TokenGenerateThread implements Runnable {
        @Override
        public void run() {
            while (true) {
                if (storedNumber.get() == maxNumber) {
                    logger.info("當前令牌數已滿");
                    try { timeUnit.sleep(genTime); }
                    catch (InterruptedException e) { e.printStackTrace(); }
                } else {
                    int old =  storedNumber.get();
                    int newValue = old + genNumber;
                    if (newValue > maxNumber)
                        newValue = maxNumber;
                    storedNumber.compareAndSet(old, newValue);
                    logger.info("生成令牌數：{}，當前令牌數：{}", genNumber, newValue);
                    try { timeUnit.sleep(genTime); }
                    catch (InterruptedException e) { e.printStackTrace(); }
                }
            }
        }
    }
}

漏桶算法

漏桶限流的實現與令牌桶限流類似，只是一個是按固定速率增加，一個按固定速率減少。

package com.dfy.ratelimiter.core;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.time.LocalDateTime;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * @description: 漏桶限流
 * @author: DFY
 * @time: 2020/4/13 14:47
 */
public class LeakyBucketLimit {

    private static Logger logger = LoggerFactory.getLogger(LeakyBucketLimit.class);

    /** 桶最大容量 */
    private int maxNumber;
    /** 時間單位，默認爲秒 */
    private TimeUnit timeUnit;
    /** 泄露的數量 */
    private int leakNumber;
    /** 泄露的時間 */
    private int leakTime;
    /** 桶中剩餘數量 */
    private AtomicInteger remainingNumber;

    public LeakyBucketLimit(int leakNumber, int leakTime, int maxNumber) {
        this(leakNumber, leakTime, TimeUnit.SECONDS, maxNumber);
    }

    public LeakyBucketLimit(int leakNumber, int leakTime, TimeUnit timeUnit, int maxNumber) {
        this.leakNumber = leakNumber;
        this.leakTime = leakTime;
        this.timeUnit = timeUnit;
        this.maxNumber = maxNumber;
        this.remainingNumber = new AtomicInteger(0);
        
    }

    public boolean tryAcquire() {
        while (true) {
            int currentStoredNumber = remainingNumber.get();
            if (currentStoredNumber == maxNumber) {
                logger.info("限流：{}", LocalDateTime.now().toString());
                return false;
            }
            if (remainingNumber.compareAndSet(currentStoredNumber, currentStoredNumber + 1)) {
                return true;
            }
        }
    }

    class LeakThread implements Runnable {
        @Override
        public void run() {
            while (true) {
                if (remainingNumber.get() == 0) {
                    logger.info("當前桶已空");
                    try { timeUnit.sleep(leakTime); }
                    catch (InterruptedException e) { e.printStackTrace(); }
                } else {
                    int old =  remainingNumber.get();
                    int newValue = old - leakNumber;
                    if (newValue < 0)
                        newValue = 0;
                    remainingNumber.compareAndSet(old, newValue);
                    logger.info("泄露：{}，當前：{}", leakNumber, newValue);
                    try { timeUnit.sleep(leakTime); }
                    catch (InterruptedException e) { e.printStackTrace(); }
                }
            }
        }
    }
}

如有問題，歡迎指正！

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