Java面试题 P17：Redis篇：Redis使用场景-缓存-缓存击穿

什么是缓存击穿：给某一个key设置了过期时间，当key过期的时候，恰好这时间点对这个key有大量的并发请求过来，这些并发的请求可能会瞬间把数据库压垮。

 

 

互斥锁代码：

package com.atguigu.boot00testredis.controller;

import com.atguigu.boot00testredis.utils.RedisUtil;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

@RestController
@RequestMapping("/hello")
public class HelloController
{
    /**
     * 注入redis工具
     */
    @Autowired
    private RedisUtil redisUtil;

    private final ReadWriteLock readWriteLock=new ReentrantReadWriteLock();
    //写锁
    private final Lock writeLock=readWriteLock.writeLock();

    @GetMapping("/hi/{name}")
    public String hi(@PathVariable("name") String name)
    {
        System.out.println("name="+name);

        if(redisUtil.get(name)!=null)
        {
            return redisUtil.get(name).toString();
        }
        else {
            //加锁
            writeLock.lock();
            System.out.println("readLock.......");
            try{
                Thread.sleep(20*1000);
                redisUtil.set(name,"My name is "+name+"!",60);
                return redisUtil.get(name).toString();
            }
            catch (Exception e)
            {
                return null;
            }
            finally {
                //开锁
                writeLock.unlock();
            }
        }
    }
}