黑马点评商户查询缓存--缓存更新策略

ShopTypeServiceImpl类 代码

package com.hmdp.service.impl;

import cn.hutool.json.JSONUtil;
import com.hmdp.dto.Result;
import com.hmdp.entity.ShopType;
import com.hmdp.mapper.ShopTypeMapper;
import com.hmdp.service.IShopTypeService;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.hmdp.utils.RedisConstants;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Service;

import java.util.List;

/**
 * 

 * 服务实现类
 * 
 *
 * @author 虎哥
 * @since 2021-12-22
 */
@Service
public class ShopTypeServiceImpl extends ServiceImpl implements IShopTypeService {
    @Autowired
    private StringRedisTemplate redisTemplate;

    @Override
    public Result queryTypeList() {
        String key = RedisConstants.CACHE_SHOP_KEY;
        //从redis中获取列表数据
        String shopType = redisTemplate.opsForValue().get(key);
        //查询到数据，直接返回
        if (shopType != null) {
            List shopTypeList = JSONUtil.toList(shopType, ShopType.class);
            return Result.ok(shopTypeList);
        }
        //未查询到，查数据库
        List shopTypeList = query().orderByAsc("sort").list();
        String jsonStr = JSONUtil.toJsonStr(shopTypeList);
        //写入redis
        redisTemplate.opsForValue().set(key,jsonStr);
        //返回数据
        return Result.ok(shopTypeList);
    }
}