学习目标：

提示：学习如何利用Redis实现添加缓存功能解决缓存穿透版

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学习产出：

缓存穿透讲解图：

解决方案：

1. 采用缓存空对象
2. 采用布隆过滤器
   解决方案流程图：
   

1. 准备pom环境

		<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-redis</artifactId></dependency><dependency><groupId>org.apache.commons</groupId><artifactId>commons-pool2</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><scope>runtime</scope><version>5.1.47</version></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><optional>true</optional></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency><dependency><groupId>com.baomidou</groupId><artifactId>mybatis-plus-boot-starter</artifactId><version>3.4.3</version></dependency><!--hutool--><dependency><groupId>cn.hutool</groupId><artifactId>hutool-all</artifactId><version>5.7.17</version></dependency>

2. 配置ThreadLocal和过滤器

public class UserHolder {private static final ThreadLocal<UserDTO> tl = new ThreadLocal<>();public static void saveUser(UserDTO user){tl.set(user);}public static UserDTO getUser(){return tl.get();}public static void removeUser(){tl.remove();}
}

@Configuration
public class MvcConfig implements WebMvcConfigurer {@Autowiredprivate StringRedisTemplate redis;@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(new LoginInterceptor()).excludePathPatterns("/user/code","/user/login","/blog/hot","/shop/**","/shop-type/**","/voucher/**").order(2);registry.addInterceptor(new RefreshTokenInterceptor(redis)).addPathPatterns("/**").order(1);}
}
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@Slf4j
public class LoginInterceptor implements HandlerInterceptor {//controller执行之前@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {//1.判断是否需要拦截ThreadLocalif (UserHolder.getUser()==null) {response.setStatus(401);return false;}//7.放行return true;}//渲染后返回给前台数据前@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {//移除用户，避免内存泄露UserHolder.removeUser();}
}
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@Slf4j
public class RefreshTokenInterceptor implements HandlerInterceptor {//这个对象不是由spring管理的所以不能用注解自动注入private StringRedisTemplate redis;public RefreshTokenInterceptor(StringRedisTemplate redis) {this.redis = redis;}//controller执行之前@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {//1.获取请求头中的tokenString token = request.getHeader("authorization");if (StrUtil.isBlank(token)) {return true;}//2.基于token获取redis中的用户//通过key取到hash中的map集合数据Map<Object, Object> userMap = redis.opsForHash().entries("login:token:" + token);//3.判断用户是否存在if (userMap.isEmpty()) {return true;}//5.将查询到的hash数据转为userDto对象UserDTO userDTO = BeanUtil.fillBeanWithMap(userMap, new UserDTO(), false);//6.存在，保存用户信息到ThreadLocal中UserHolder.saveUser(userDTO);//7.刷新token有效期redis.expire(LOGIN_USER_KEY + token, 30, TimeUnit.MINUTES);log.info("我是第一个拦截器当前拦截所有请求的用户为，线程为{},{}",UserHolder.getUser(),Thread.currentThread());//8.放行return true;}

3. Controller层：负责接收请求和向下分配

@RestController
@RequestMapping("/shop")
public class ShopController {@Resourcepublic 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.queryShopById(id));}
}

4. Service层：负责业务的处理逻辑

@Service
@Slf4j
public class ShopServiceImpl extends ServiceImpl<ShopMapper, Shop> implements IShopService {@Resourceprivate StringRedisTemplate redis;public Result queryShopById(Long id) {//1.从Redis查询数据缓存String shopCache = redis.opsForValue().get("cache:shop:" + id);//2.判断是否存在 当shopCache为“”时返回falseif (StrUtil.isNotBlank(shopCache)) {//3.存在，直接返回Shop shop = JSONUtil.toBean(shopCache, Shop.class);return Result.ok(shop);}//判断命中的是否是空值if (shopCache!=null) {return Result.fail(" 店铺信息不存在 ");}//4.不存在，根据id查询数据库Shop shop = getById(id);if (ObjectUtil.isEmpty(shop)) {// 解决缓存穿透redis.opsForValue().set("cache:shop:" + id,"",2,TimeUnit.MINUTES);//5.不存在，返回错误return Result.fail("当前商户不存在");}//6.存在，写入redisredis.opsForValue().set("cache:shop:"+id,JSONUtil.toJsonStr(shop));redis.expire("cache:shop:"+id,30,TimeUnit.MINUTES);//7.返回return Result.ok(shop);}
}