Redis

 

 

 

 

封装缓存空对象解决缓存穿透与逻辑过期解决缓存击穿工具类

@Slf4j
@Component
public class CacheClient {

    private final StringRedisTemplate stringRedisTemplate;
    public CacheClient(StringRedisTemplate stringRedisTemplate) {
        this.stringRedisTemplate = stringRedisTemplate;
    }

    public void set(String key, Object value , Long time, TimeUnit unit) {
        stringRedisTemplate.opsForValue().set(key, JSONUtil.toJsonStr(value), time, unit);
    }

    public void setWithLogicalExpire(String key, Object value , Long time, TimeUnit unit) {
        //设置逻辑过期时间
        RedisData redisData = new RedisData();
        redisData.setData(value);
        redisData.setExpireTime(LocalDateTime.now().plusSeconds(unit.toSeconds(time)));
        //写入Redis
        stringRedisTemplate.opsForValue().set(key, JSONUtil.toJsonStr(redisData));
    }
    //解决缓存穿透的代码
    public <R, ID> R queryWithPassThrough(String keyPrefix, ID id, Class<R> type, Function<ID, R> dbFallback, Long time, TimeUnit unit) {
        String key = keyPrefix + id;
        //1.从redis查询商铺缓存
        String json = stringRedisTemplate.opsForValue().get(key);
        //2.判断是否存在
        if (StrUtil.isNotBlank(json)) {
            //3.存在，直接返回
            return JSONUtil.toBean(json, type);
        }
        //判断命中的是否是空值，不为null 就为“” 因为存入的为“”  解决缓存穿透
        if(json != null){
            return null;
        }
        //4.不存在，根据id查询数据库
        QueryWrapper<Shop> queryWrapper = new QueryWrapper<>();
        queryWrapper.eq("id", id);
        R r = dbFallback.apply(id);
        //5.不存在，返回错误
        if(r == null){
            //将空值写入redis
            stringRedisTemplate.opsForValue().set(key,"",CACHE_NULL_TTL,TimeUnit.MINUTES);
            return null;
        }
        //6.存在，写入redis
        this.set(key, r, time, unit);
        //7.返回
        return r;
    }

    //创建指定上线的线程池
    private static final ExecutorService CACHE_REBUILD_EXECUTOR = Executors.newFixedThreadPool(10);
    //逻辑过期解决缓存击穿
    public <R, ID> R queryWithLogicalExpire(String keyPrefix, ID id, Class<R> type, Function<ID, R> dbFallback, Long time, TimeUnit unit) {
        String key = keyPrefix + id;
        //1.从redis查询商铺缓存
        String json = stringRedisTemplate.opsForValue().get(key);
        //2.判断是否存在
        if (StrUtil.isBlank(json)) {
            return null;
        }
        //4.命中，先把json反序列化为对象
        RedisData redisData = JSONUtil.toBean(json, RedisData.class);
        R r = JSONUtil.toBean((JSONObject) redisData.getData(), type);
        LocalDateTime expireTime = redisData.getExpireTime();
        //5.判断缓存是否过期
        if(expireTime.isAfter(LocalDateTime.now())){
            //5.1未过期，直接返回店铺信息
            return r;
        }
        //5.2已过期，需要缓存重建
        //6.缓存重建
        //6.1获取互斥锁
        boolean isLock = tryLock(LOCK_SHOP_KEY + id);
        //6.2判断是否获取互斥锁成功
        if(isLock){
            //6.3成功，开启独立线程，实现缓存重建
            CACHE_REBUILD_EXECUTOR.submit(() ->{
                try {
                    //查询数据库
                    R r1 = dbFallback.apply(id);
                    //写入redis
                    this.setWithLogicalExpire(key, r1, time, unit);
                } catch (Exception e) {
                    throw new RuntimeException(e);
                } finally {
                    //释放锁
                    unlock(LOCK_SHOP_KEY + id);
                }
            });
        }
        //6.4失败与成功，都返回过期的商铺信息
        return r;
    }
    //获取锁方法
    private boolean tryLock(String key){
        Boolean b = stringRedisTemplate.opsForValue().setIfAbsent(key, "1", 10, TimeUnit.SECONDS);
        //方法的返回值为基本类型，需将b进行拆箱，拆箱过程中可能会出现空指针异常，所以要使用工具类
        return BooleanUtil.isTrue(b);//会进行自动拆箱（当传入的值是 null 时，它会返回 false。可以避免空指针异常，这里没用到）
    }
    //释放锁方法
    private void unlock(String key){
        stringRedisTemplate.delete(key);
    }
}

控制层调用

    @GetMapping("/{id}")
    public Result queryShopById(@PathVariable("id") Long id) {
        return shopService.queryById(id);
    }

服务层调用

Result queryById(Long id);

    @Override
    public Result queryById(Long id){
        //缓存穿透
//        Shop shop = cacheClient.queryWithPassThrough(CACHE_SHOP_KEY, id ,Shop.class, this::getById, CACHE_SHOP_TTL, TimeUnit.MINUTES);

        //互斥锁解决缓存击穿
        //Shop shop = queryWithMutex(id);
        //逻辑过期解决缓存击穿
        //缓存击穿测试时，需先用测试类添加数据到数据库
        Shop shop = cacheClient
                .queryWithLogicalExpire(CACHE_SHOP_KEY, id , Shop.class, this::getById, CACHE_SHOP_TTL, TimeUnit.MINUTES);
        if(shop == null){
            return Result.fail("店铺不存在");
        }
        //返回
        return Result.ok(shop);
    }

常量工具类

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;
}

数据工具类

@Data
public class RedisData {
    private LocalDateTime expireTime;
    private Object data;
}

 

 

互斥锁解决缓存击穿

//互斥所解决缓存击穿
    public Shop queryWithMutex(Long id) {
        //1.从redis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，不为null 就为“”  解决缓存穿透
        if(shopJson != null){
            return null;
        }
        Shop shop = null;
        try {
            //4.实现缓存重建
            //4.1 获取互斥锁
            boolean isLock = tryLock(LOCK_SHOP_KEY + id);
            //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
            QueryWrapper<Shop> queryWrapper = new QueryWrapper<>();
            queryWrapper.eq("id", id);
            shop = shopMapper.selectOne(queryWrapper);
            //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redis
                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.释放互斥锁
            unlock(LOCK_SHOP_KEY + id);
        }
        //7.返回
        return shop;
    }

    //获取锁方法
    private boolean tryLock(String key){
        Boolean b = stringRedisTemplate.opsForValue().setIfAbsent(key, "1", 10, TimeUnit.SECONDS);
        //方法的返回值为基本类型，需将b进行拆箱，拆箱过程中可能会出现空指针异常，所以要使用工具类
        return BooleanUtil.isTrue(b);//会进行自动拆箱（当传入的值是 null 时，它会返回 false。可以避免空指针异常，这里没用到）
    }
    //释放锁方法
    private void unlock(String key){
        stringRedisTemplate.delete(key);
    }

原文地址：https://blog.csdn.net/weixin_53515812/article/details/142644338

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