Java面试之限流的实现方式小结

import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;

public class SemaphoreExample {

    private final Semaphore semaphore = new Semaphore(5); // 只允许5个线程同时访问

    public void accessResource() {
        try {
            semaphore.acquire(); // 获取许可，如果当前许可数不足，则会阻塞
            System.out.println(Thread.currentThread().getName() + "获得了许可，正在访问资源...");
            // 模拟访问资源的时间消耗
            Thread.sleep(2000);
            System.out.println(Thread.currentThread().getName() + "访问资源结束，释放许可...");
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            e.printStackTrace();
        } finally {
            semaphore.release(); // 访问结束后释放许可
        }
    }

    public static void main(String[] args) {
        SemaphoreExample example = new SemaphoreExample();

        for (int i = 0; i < 10; i++) {
            new Thread(() -> example.accessResource()).start();
        }
    }
}

<!-- https://mvnrepository.com/artifact/com.google.guava/guava -->
<dependency>
  <groupId>com.google.guava</groupId>
  <artifactId>guava</artifactId>
  <version>28.2-jre</version>
</dependency>

import com.google.common.util.concurrent.RateLimiter;
import java.time.Instant;

/**
 * Guava 实现限流
 */
public class RateLimiterExample {
    public static void main(String[] args) {
        // 每秒产生 10 个令牌（每 100 ms 产生一个）
        RateLimiter rt = RateLimiter.create(10);
        for (int i = 0; i < 11; i++) {
            new Thread(() -> {
                // 获取 1 个令牌，获取到令牌就执行，否则就阻塞等待
                rt.acquire();
                System.out.println("正常执行方法，ts:" + Instant.now());
            }).start();
        }
    }
}

<dependency>
  <groupId>com.alibaba.cloud</groupId>
  <artifactId>spring-cloud-starter-alibaba-sentinel</artifactId>
</dependency>
<dependency>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-starter-gateway</artifactId>
</dependency>
<dependency>
  <groupId>com.alibaba.cloud</groupId>
  <artifactId>spring-cloud-alibaba-sentinel-gateway</artifactId>
</dependency>

spring:
  application:
    name: gate-way-blog
  cloud:
    sentinel:
      transport:
        dashboard: localhost:18080
      scg: # 配置限流之后，响应内容
        fallback:
          # 两种模式，一种是 response 返回文字提示信息，
          # 另一种是 redirect 重定向跳转，不过配置 redirect 也要配置对应的跳转的 uri
          mode: response
          # 响应的状态
          response-status: 200
          # 响应体
          response-body: '{"code": -10,"message": "被熔断或限流！"}'

limit_req_zone $binary_remote_addr zone=mylimit:10m rate=2r/s;
server {
  location / {
    limit_req zone=mylimit;
  }
}

limit_req_zone $binary_remote_addr zone=mylimit:10m rate=2r/s;
server {
  location / {
    limit_req zone=mylimit burst=4;
  }
}

limit_conn_zone $binary_remote_addr zone=perip:10m;
limit_conn_zone $server_name zone=perserver:10m;
server {
  ...
  limit_conn perip 10;
  limit_conn perserver 100;
}