学习目标：
提示：学习如何利用Redis逻辑过期实现添加缓存功能解决缓存击穿
学习产出：
缓存击穿讲解图：
解决方案：
- 采用互斥锁
- 采用逻辑过期
1. 准备pom环境
java
<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
java
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();
}
}
java
@Configuration
public class MvcConfig implements WebMvcConfigurer {
@Autowired
private StringRedisTemplate redis;
@Override
public 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);
}
}
---------------------------------------------
@Slf4j
public class LoginInterceptor implements HandlerInterceptor {
//controller执行之前
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
//1.判断是否需要拦截ThreadLocal
if (UserHolder.getUser()==null) {
response.setStatus(401);
return false;
}
//7.放行
return true;
}
//渲染后返回给前台数据前
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
//移除用户，避免内存泄露
UserHolder.removeUser();
}
}
---------------------------------------------------
@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
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
//1.获取请求头中的token
String 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. RedisData接收数据
java
@Data
public class RedisData {
private LocalDateTime expireTime;
private Object data;
}3. Controller层：负责接收请求和向下分配
java
@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.queryShopById(id));
}
}4. Service层：负责业务的处理逻辑
java
@Service
@Slf4j
public class ShopServiceImpl extends ServiceImpl<ShopMapper, Shop> implements IShopService {
@Resource
private StringRedisTemplate redis;
private static final ExecutorService EXECUTOR_SERVICE = Executors.newFixedThreadPool(10);
private boolean tryLock(String key) {
Boolean setnx = redis.opsForValue().setIfAbsent(key, "1", 10, TimeUnit.MINUTES);
return BooleanUtil.isTrue(setnx);
}
private void unlock(String key) {
redis.delete(key);
}
public Result queryShopById(Long id) {
Shop shop = queryShopWithLogicExpire(id);
if (shop == null) {
return Result.fail("店铺不存在");
}
return Result.ok(shop);
}
//利用逻辑过期解决缓存击穿问题
private Shop queryShopWithLogicExpire(Long id) {
//1.从Redis查询商品缓存
String cacheShop = redis.opsForValue().get("cache:shop:" + id);
//2.未命中
if (ObjectUtil.isEmpty(cacheShop)) {
return null;
}
//3.命中
RedisData redisDataWithShop = JSONUtil.toBean(cacheShop, RedisData.class);
LocalDateTime expireTime = redisDataWithShop.getExpireTime();
JSONObject shopData = (JSONObject) redisDataWithShop.getData();
Shop shop = JSONUtil.toBean(shopData, Shop.class);
//3.1判断缓存是否过期
if (expireTime.isAfter(LocalDateTime.now())) {
//3.2未过期,返回
return shop;
}
//4.已过期，需要重建缓存
//5.缓存重建
//5.1获取互斥锁
String lock = "lock:shop:" + id;
boolean isLock = tryLock(lock);
//5.2判断互斥锁是否成功
if (isLock) {
// TODO: 2023/8/9 //5.3成功，开启独立线程，实现缓存重建
CACHE_REBUILD_EXECUTOR.submit(() -> {
//缓存重构
try {
Shop shopItem = getById(id);
RedisData redisData = new RedisData();
redisData.setData(shopItem);
redisData.setExpireTime(LocalDateTime.now().plusSeconds(180L));
redis.opsForValue().set("cache:shop:" + id, JSONUtil.toJsonStr(redisData));
} finally {
unlock(lock);
}
});
}
//5.4返回过期商铺信息
return shop;
}
}