1、什么是缓存

缓存就是数据交换的缓冲区（称为Cache），是存贮数据的临时地方，一般读写性能较高。

2、添加商户缓存

3、前端接口

http://127.0.0.1:8080/api/shop/1

4、ShopController.java

package com.hmdp.controller;


import cn.hutool.core.util.StrUtil;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.hmdp.dto.Result;
import com.hmdp.entity.Shop;
import com.hmdp.service.IShopService;
import com.hmdp.utils.SystemConstants;
import org.springframework.web.bind.annotation.*;

import javax.annotation.Resource;

/**
 * <p>
 * 前端控制器
 * </p>
 */
@RestController
@RequestMapping("/shop")
public class ShopController {

    @Resource
    public IShopService shopService;

    /**
     * 根据id查询商铺信息
     * @param id 商铺id
     * @return 商铺详情数据
     */
    @GetMapping("/{id}")
    public Result queryShopById(@PathVariable("id") Long id) {
        //return Result.ok(shopService.getById(id));
        return shopService.queryById(id);
    }

    /**
     * 新增商铺信息
     * @param shop 商铺数据
     * @return 商铺id
     */
    @PostMapping
    public Result saveShop(@RequestBody Shop shop) {
        // 写入数据库
        shopService.save(shop);
        // 返回店铺id
        return Result.ok(shop.getId());
    }

    /**
     * 更新商铺信息
     * @param shop 商铺数据
     * @return 无
     */
    @PutMapping
    public Result updateShop(@RequestBody Shop shop) {
        // 写入数据库
        shopService.updateById(shop);
        return Result.ok();
    }

    /**
     * 根据商铺类型分页查询商铺信息
     * @param typeId 商铺类型
     * @param current 页码
     * @return 商铺列表
     */
    @GetMapping("/of/type")
    public Result queryShopByType(
            @RequestParam("typeId") Integer typeId,
            @RequestParam(value = "current", defaultValue = "1") Integer current
    ) {
        // 根据类型分页查询
        Page<Shop> page = shopService.query()
                .eq("type_id", typeId)
                .page(new Page<>(current, SystemConstants.DEFAULT_PAGE_SIZE));
        // 返回数据
        return Result.ok(page.getRecords());
    }

    /**
     * 根据商铺名称关键字分页查询商铺信息
     * @param name 商铺名称关键字
     * @param current 页码
     * @return 商铺列表
     */
    @GetMapping("/of/name")
    public Result queryShopByName(
            @RequestParam(value = "name", required = false) String name,
            @RequestParam(value = "current", defaultValue = "1") Integer current
    ) {
        // 根据类型分页查询
        Page<Shop> page = shopService.query()
                .like(StrUtil.isNotBlank(name), "name", name)
                .page(new Page<>(current, SystemConstants.MAX_PAGE_SIZE));
        // 返回数据
        return Result.ok(page.getRecords());
    }
}

5、ShopServiceImpl.java

package com.hmdp.service.impl;

import cn.hutool.core.util.StrUtil;
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 org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Service;
import javax.annotation.Resource;
import static com.hmdp.utils.RedisConstants.CACHE_SHOP_KEY;

/**
 * <p>
 *  服务实现类
 * </p>
 */
@Service
public class ShopServiceImpl extends ServiceImpl<ShopMapper, Shop> implements IShopService {
    @Resource
    private StringRedisTemplate stringRedisTemplate;

    @Override
    public Result queryById(Long id) {
        String key = CACHE_SHOP_KEY + id;
        //1、从redis查询商铺缓存
        String shopJson = stringRedisTemplate.opsForValue().get(key);
        //2、判断是否存在
        if (StrUtil.isNotBlank(shopJson)) {
            //3、存在，直接返回
            Shop shop = JSONUtil.toBean(shopJson, Shop.class);
            return Result.ok(shop);
        }

        //4、不存在，根据id查询数据库
        Shop shop = getById(id);
        //5、数据库不存在，返回错误
        if (shop == null) {
            return Result.fail("店铺不存在!");
        }
        //6、存在，写入redis
        stringRedisTemplate.opsForValue().set(key, JSONUtil.toJsonStr(shop));
        //7、返回
        return Result.ok(shop);
    }
}

6、RedisConstants.java

package com.hmdp.utils;

public class RedisConstants {
    public static final String LOGIN_CODE_KEY = "login:code:";
    public static final Long LOGIN_CODE_TTL = 2L;
    public static final String LOGIN_USER_KEY = "login:token:";
    public static final Long LOGIN_USER_TTL = 36000L;

    public static final Long CACHE_NULL_TTL = 2L;

    public static final Long CACHE_SHOP_TTL = 30L;
    public static final String CACHE_SHOP_KEY = "cache:shop:";

    public static final String LOCK_SHOP_KEY = "lock:shop:";
    public static final Long LOCK_SHOP_TTL = 10L;

    public static final String SECKILL_STOCK_KEY = "seckill:stock:";
    public static final String BLOG_LIKED_KEY = "blog:liked:";
    public static final String FEED_KEY = "feed:";
    public static final String SHOP_GEO_KEY = "shop:geo:";
    public static final String USER_SIGN_KEY = "sign:";
}

7、查看Redis Desktop Manager