Redis双重检验同步代码块解决缓存击穿

小咪咪 2021-10-23 14:34 374阅读 0赞

import bootandredis.demo.mapper.BookMapper;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Controller;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.bind.annotation.ResponseBody;
    import redis.clients.jedis.Jedis;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    
    /*在springboot下进行Redis测试
    * 浏览器访问127.0.0.1:8080/redis启动测试*/
    @Controller
    public class condemo {
        @Autowired
        private BookMapper bookMapper;
    
        @RequestMapping("/redis")
        @ResponseBody
        public String con01() {
            //创建线程实例
            Runnable runnable = new Runnable() {
                @Override
                public void run() {
                    //调用需要测试的方法
                    getBooks();
                }
            };
            // 多线程测试缓存穿透，设置启动线程数为25
            ExecutorService executorService = Executors.newFixedThreadPool(25);
            //利用25个线程循环启动5000次
            for (int i = 0; i < 5000; i++)
                executorService.submit(runnable);
    
            return "over";
        }
    
        public void getBooks() {
            //启动Jedis连接Redis
            Jedis j = new Jedis("192.168.37.134", 6379);
            //验证登录密码
            j.auth("123456");
            
            String s = j.get("books");
            
            //双重验证以确保数据库只被查询一次，避免缓存穿透
            if (null == s)
                synchronized (this) {
                    s = j.get("books");
                    if (null == s) {
                        s = bookMapper.selectAll().toString();
                        j.set("books", s);
                        System.out.println("查询数据库");
                    }else
                        System.out.println("查询redis");
                }
            else {
                System.out.println("查询redis");
            }
    
        }
    }