coding++：高并发解决方案限流技术-使用RateLimiter实现令牌桶限流-Demo

RateLimiter是guava提供的基于令牌桶算法的实现类，可以非常简单的完成限流特技，并且根据系统的实际情况来调整生成token的速率。

通常可应用于抢购限流防止冲垮系统；限制某接口、服务单位时间内的访问量，譬如一些第三方服务会对用户访问量进行限制；限制网速，单位时间内只允许上传下载多少字节等。

guava的maven依赖

<dependency>
     <groupId>com.google.guava</groupId>
     <artifactId>guava</artifactId>
     <version>25.1-jre</version>
 </dependency>

令牌桶的原理，有一个独立线程一直以一个固定的速率往桶中存放令牌客户端去桶中获取令牌，获取到令牌，就可以访问，获取不到，说明请求过多，需要服务降级。

package com.aiyuesheng.controller;

import java.util.concurrent.TimeUnit;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.aiyuesheng.hystrix.OrderHystrixCommand;
import com.aiyuesheng.service.OrderService;
import com.aiyuesheng.utils.LimitService;
import com.alibaba.fastjson.JSONObject;
import com.google.common.util.concurrent.RateLimiter;

@RestController
public class Index {// 令牌桶：1.0 表示 每秒中生成1个令牌存放在桶中
    RateLimiter rateLimiter = RateLimiter.create(1.0);

    @Autowired
    private OrderService orderService;
//令牌桶限流
    @RequestMapping("/searchCustomerInfoByRateLimiter")
    public Object searchCustomerInfoByRateLimiter() {
        // 1.限流判断
        // 如果在0.5秒内 没有获取不到令牌的话，则会一直等待
        System.out.println("生成令牌等待时间:" + rateLimiter.acquire());
        boolean acquire = rateLimiter.tryAcquire(500, TimeUnit.MILLISECONDS); // 每次发送请求，愿意等待0.5秒，如果设为1秒，每次都能查询成功，因为没秒中都会放入一个令牌到桶中
        if (!acquire) {
            System.out.println("稍后再试！");
            return "稍后再试！";
        }
        // 2.如果没有达到限流的要求,直接调用接口查询
        System.out.println(orderService.searchCustomerInfo());
        return orderService.searchCustomerInfo();
    }

}

基于 AOP 实现：

package com.tree.ztree_demo.currentlimiting;

import java.lang.annotation.*;

/**
 * @version V1.0
 * @Title: RateLimit.java
 * @Package mlq.pic.picback.currentlimiting
 * @Description: 限流注解
 * @author: MLQ
 * @date: 2019/11/14 14:52
 */
@Inherited
@Documented
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface RateLimit {

    /**
     * 默认每秒支持2个
     *
     * @return
     */
    int limintNum() default 2;


}

-----

package com.tree.ztree_demo.currentlimiting;

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.google.common.util.concurrent.RateLimiter;
import groovy.util.logging.Slf4j;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.Signature;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;
import org.aspectj.lang.reflect.MethodSignature;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;
import org.springframework.util.ObjectUtils;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.TimeUnit;

/**
 * @version V1.0
 * @Title: RateLimitAspect.java
 * @Package mlq.pic.picback.currentlimiting
 * @Description: 增强限流拦截
 * @author: MLQ
 * @date: 2019/11/14 14:54
 */
@Component
@Scope
@Aspect
@Slf4j
public class RateLimitAspect {

    private static final Logger LOGGER = LoggerFactory.getLogger(RateLimitAspect.class);

    /**
     * 用来存放不同接口的RateLimiter(key为接口名称，value为RateLimiter)
     */
    private ConcurrentHashMap<String, RateLimiter> map = new ConcurrentHashMap<>();

    private static final String POINT = "execution (* com.tree.ztree_demo..*.abc*(..))";

    private static ObjectMapper objectMapper = new ObjectMapper();

    private RateLimiter rateLimiter;

    @Autowired
    private HttpServletResponse response;

    @Pointcut(POINT)
    public void serviceLimit() {
    }

    @Around("serviceLimit()")
    public Object around(ProceedingJoinPoint joinPoint) throws NoSuchMethodException {
        Object obj = null;
        //获取拦截的方法名
        Signature sig = joinPoint.getSignature();
        //获取拦截的方法名
        MethodSignature msig = (MethodSignature) sig;
        //返回被织入增加处理目标对象
        Object target = joinPoint.getTarget();
        //为了获取注解信息
        Method currentMethod = target.getClass().getMethod(msig.getName(), msig.getParameterTypes());
        //获取注解信息
        RateLimit annotation = currentMethod.getAnnotation(RateLimit.class);
        if (!ObjectUtils.isEmpty(annotation)) {
            //获取注解每秒加入桶中的token
            int limitNum = annotation.limintNum();

            // 注解所在方法名区分不同的限流策略
            String functionName = msig.getName();

            //获取rateLimiter
            if (map.containsKey(functionName)) {
                rateLimiter = map.get(functionName);
            } else {
                map.put(functionName, RateLimiter.create(limitNum));
                rateLimiter = map.get(functionName);
            }
            // 如果在0.5秒内 没有获取不到令牌的话，则会一直等待
            System.out.println("生成令牌等待时间:" + rateLimiter.acquire());
            try {
                // 每次发送请求，愿意等待0.5秒，如果设为1秒，每次都能查询成功，因为没秒中都会放入一个令牌到桶中
                if (rateLimiter.tryAcquire(500, TimeUnit.MILLISECONDS)) {
                    //执行方法
                    obj = joinPoint.proceed();
                } else {
                    Map<String, Object> map = new HashMap<>();
                    map.put("code", 100001);
                    map.put("message", "系统繁忙，请稍后再试！");
                    //拒绝了请求（服务降级）
                    String result = objectMapper.writeValueAsString(map);
                    LOGGER.info("拒绝了请求：" + result);
                    outErrorResult(result);
                }
            } catch (Throwable throwable) {
                throwable.printStackTrace();
            }
        } else {
            Map<String, Object> map = new HashMap<>();
            map.put("code", 403);
            map.put("message", "签名问题");
            //拒绝了请求（服务降级）
            String result = null;
            try {
                result = objectMapper.writeValueAsString(map);
            } catch (JsonProcessingException e) {
                e.printStackTrace();
            }
            LOGGER.info("拒绝了请求：" + result);
            outErrorResult(result);
        }
        return obj;
    }

    //将结果返回
    public void outErrorResult(String result) {
        response.setContentType("application/json;charset=UTF-8");
        try (ServletOutputStream outputStream = response.getOutputStream()) {
            outputStream.write(result.getBytes("utf-8"));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    static {
        objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
    }

}

使用方式：在controller 访问地址加上注解即可

@RateLimit(limintNum = 100)
@RequestMapping("abc")
public Object abc() {
    Map<String, Object> map = new HashMap<>();
    map.put("code", "200");
    map.put("message", "OK");
    return JSON.toJSONString(map);
}

coding++：高并发解决方案限流技术-使用RateLimiter实现令牌桶限流-Demo

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