redis学习系列--Redis 高并发下的，缓存穿透问题解决方案

一时失言乱红尘 2022-05-14 03:38 151阅读 0赞

### **下面这段代码 如果1W个人同时访问的话,  从redis 拿 allUser 时， userList为空时，那么1W个人都要进入if判断语句，查询数据库，数据库压力承受不住** ###

package com.tb.service;
     
    import com.tb.dao.TUserMapper;
    import com.tb.pojo.TUser;
    import org.springframework.data.redis.core.RedisTemplate;
    import org.springframework.stereotype.Service;
    import org.springframework.transaction.annotation.Transactional;
     
    import javax.annotation.Resource;
    import java.util.List;
     
    @Service
    @Transactional
    public class TuserServicelmpl implements  TuserService {
     
        @Resource
        private TUserMapper  tUserMapper;
     
        @Resource
        private RedisTemplate  redisTemplate;
     
        @Override
        public List<TUser> userlist() {
     
            //高并发下有点问题，此处问题：缓存穿透
            //查询缓存
            List<TUser>  userList =  ( List<TUser>) redisTemplate.opsForValue().get("allUser");
            if (userList==null){
                //查询数据库
                userList =  tUserMapper.userlist();
                redisTemplate.opsForValue().set("allUser",userList);
            }
            return userList;
        }
    }

# 解决方案 #

###      Synchronized   关键字 ###

双重检测锁 解决

package com.tb.service;
     
    import com.tb.dao.TUserMapper;
    import com.tb.pojo.TUser;
    import org.springframework.data.redis.core.RedisTemplate;
    import org.springframework.stereotype.Service;
    import org.springframework.transaction.annotation.Transactional;
     
    import javax.annotation.Resource;
    import java.util.List;
     
    @Service
    @Transactional
    public class TuserServicelmpl implements  TuserService {
     
        @Resource
        private TUserMapper  tUserMapper;
     
        @Resource
        private RedisTemplate  redisTemplate;
     
        @Override
        public List<TUser> userlist() {
     
            //高并发下有点问题，此处问题：缓存穿透
            //查询缓存
            List<TUser>  userList =  ( List<TUser>) redisTemplate.opsForValue().get("allUser");
     
            //双重检测锁
            if (userList==null){
                synchronized(this){
                    //从数据库获取数据
                    userList =  ( List<TUser>) redisTemplate.opsForValue().get("allUser");
                    if (userList==null){
                        //缓存为空，查询数据库
                        userList =  tUserMapper.userlist();
                        redisTemplate.opsForValue().set("allUser",userList);
                    }
                }
     
     
            }
            return userList;
        }
    }