redis实现缓存2-解决缓存穿透，缓存击穿

具体实现：
ShopServiceImpl

package com.hmdp.service.impl;

import cn.hutool.core.util.BooleanUtil;
import cn.hutool.core.util.StrUtil;
import cn.hutool.json.JSONObject;
import cn.hutool.json.JSONUtil;
import com.hmdp.dto.Result;
import com.hmdp.entity.Shop;
import com.hmdp.mapper.ShopMapper;
import com.hmdp.service.IShopService;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.hmdp.utils.RedisData;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import javax.annotation.Resource;

import java.time.LocalDateTime;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

import static com.hmdp.utils.RedisConstants.*;

/**
 * <p>
 *  服务实现类
 * </p>
 *
 * @author ztn
 * @since 2025-9-12
 */
@Service
public class ShopServiceImpl extends ServiceImpl<ShopMapper, Shop> implements IShopService {

    @Resource
    StringRedisTemplate stringRedisTemplate;

    @Override
    public Result queryById(Long id) {

        // 缓存穿透
        // Shop shop = queryWithPassThrough(id);
        // 互斥锁解决缓存击穿
        // Shop shop = queryWithMutex(id);
        // 逻辑过期解决缓存击穿
        Shop shop = queryWithLogicalExpire(id);

        if (shop == null) {
            return Result.fail("店铺不存在！");
        }

        // 7.返回
        return Result.ok(shop);
    }

    private static final ExecutorService CACHE_REBUILD_EXECUTOR = Executors.newFixedThreadPool(10);

    public Shop queryWithLogicalExpire(Long id){
        // 1.从redis中查询商铺缓存
        String shopJson = stringRedisTemplate.opsForValue().get(CACHE_SHOP_KEY + id);
        // 2.判断是否存在
        if(StrUtil.isBlank(shopJson)){
            // 3.存在，直接返回
            return null;
        }

        // 4.命中，把json反序列化为对象
        RedisData redisData = JSONUtil.toBean(shopJson, RedisData.class);
        Shop shop = JSONUtil.toBean((JSONObject) redisData.getData(), Shop.class);
        LocalDateTime expireTime = redisData.getExpireTime();
        // 5.判断是否过期
        if(expireTime.isAfter(LocalDateTime.now())){
            // 5.1未过期，直接返回店铺信息
            return shop;
        }
        // 5.2过期，要缓存重建
        // 6.重建缓存
        // 6.1获取互斥锁
        String lockKey = LOCK_SHOP_KEY +id;
        boolean isLock = tryLock(lockKey);
        // 6.2 判断是否获取锁成功
        if(isLock){
            // 6.3 成功，开启独立线程
            CACHE_REBUILD_EXECUTOR.submit(()->{
                try {
                    this.saveShop2Redis(id,20L);
                } catch (Exception e) {
                    throw new RuntimeException(e);
                } finally {
                    //释放锁
                    unlock(lockKey);
                }

            });
        }
        // 6.4 返回过期的店铺信息
        return shop;
    }


    private boolean tryLock(String key){
        Boolean flag = stringRedisTemplate.opsForValue().setIfAbsent(key, "1", 10, TimeUnit.SECONDS);
        return BooleanUtil.isTrue(flag);
    }

    private void unlock(String key){
        stringRedisTemplate.delete(key);

    }

    public Shop queryWithMutex(Long id){
        // 1.从redis中查询商铺缓存
        String shopJson = stringRedisTemplate.opsForValue().get(CACHE_SHOP_KEY + id);
        // 2.判断是否存在
        if(StrUtil.isNotBlank(shopJson)){
            // 3.存在，直接返回
            return JSONUtil.toBean(shopJson, Shop.class);
        }
        // 判断命中的是否是空值
        if(shopJson != null){
            return null;
        }
        // 4.实现缓存重建
        // 4.1获取互斥锁
        String lockKey = LOCK_SHOP_KEY +id;
        Shop shop = null;
        try {
            boolean isLock = tryLock(lockKey);
            // 4.2判断是否获取成功
            if(!isLock){
                // 4.3失败，则休眠并重试
                Thread.sleep(50);
                return queryWithMutex(id);
            }
            // 4.4成功，根据id查询数据库
            shop = getById(id);
            //模拟重建的延时
            Thread.sleep(200);
            // 5.不存在，返回错误
            if(shop == null){

                //将空值写入reids
                stringRedisTemplate.opsForValue().set(CACHE_SHOP_KEY + id, "",CACHE_NULL_TTL, TimeUnit.MINUTES);

                return null;
            }
            // 6.存在，写入redis
            stringRedisTemplate.opsForValue().set(CACHE_SHOP_KEY + id, JSONUtil.toJsonStr(shop),CACHE_SHOP_TTL, TimeUnit.MINUTES);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }finally {
            // 7.返回
            unlock(lockKey);
        }
        // 8.返回
        return shop;
    }

    public Shop queryWithPassThrough(Long id){
        // 1.从redis中查询商铺缓存
        String shopJson = stringRedisTemplate.opsForValue().get(CACHE_SHOP_KEY + id);
        // 2.判断是否存在
        if(StrUtil.isNotBlank(shopJson)){
            // 3.存在，直接返回
            return JSONUtil.toBean(shopJson, Shop.class);
        }
        // 判断命中的是否是空值
        if(shopJson != null){
            return null;
        }
        // 4.不存在，根据id查询数据库
        Shop shop = getById(id);
        // 5.不存在，返回错误
        if(shop == null){

            //将空值写入reids
            stringRedisTemplate.opsForValue().set(CACHE_SHOP_KEY + id, "",CACHE_NULL_TTL, TimeUnit.MINUTES);

            return null;
        }
        // 6.存在，写入redis
        stringRedisTemplate.opsForValue().set(CACHE_SHOP_KEY + id, JSONUtil.toJsonStr(shop),CACHE_SHOP_TTL, TimeUnit.MINUTES);
        // 7.返回
        return shop;
    }



    public void saveShop2Redis(Long id, Long expireSeconds) throws InterruptedException {

        // 1.查询店铺数据
        Shop shop = getById(id);
        Thread.sleep(200);
        // 2.封装逻辑过期时间
        RedisData redisData = new RedisData();
        redisData.setData(shop);
        redisData.setExpireTime(LocalDateTime.now().plusSeconds(expireSeconds));
        // 3.写入redis
        stringRedisTemplate.opsForValue().set(CACHE_SHOP_KEY + id, JSONUtil.toJsonStr(redisData));
    }





    @Override
    @Transactional
    public Result update(Shop shop) {
        Long id = shop.getId();
        if (id == null) {
            return Result.fail("店铺id不能为空");
        }
        // 1.更新数据库
        updateById(shop);
        // 2.删除缓存
        stringRedisTemplate.delete(CACHE_SHOP_KEY + id);
        return Result.ok();
    }
}