springboot(19)Redis缓存@Cacheable对存在的数据返回null

ゝ一世哀愁。 2022-05-19 14:43 241阅读 0赞

### 问题描述 ###

Spring Cache + redis做缓存，使用的是1.8.10.RELEASE版本的spring-data-redis。在高并发下数据库存在数据但是@Cacheable 注解返回的内容是null。查看了一下源代码，在使用注解获取缓存的时候，RedisCache的get方法会先去判断key是否存在，然后再去获取值。这了就有一个漏铜，当线程1判断了key是存在的，紧接着这个时候这个key过期了，这时线程1再去获取值的时候返回的是null。

org.springframework.data.redis.cache.RedisCache.get(RedisCacheKey)方法源码：

public RedisCacheElement get(final RedisCacheKey cacheKey) {
    
        Assert.notNull(cacheKey, "CacheKey must not be null!");
    
        Boolean exists = (Boolean) redisOperations.execute(new RedisCallback<Boolean>() {
    
            @Override
            public Boolean doInRedis(RedisConnection connection) throws DataAccessException {
                return connection.exists(cacheKey.getKeyBytes());
            }
        });
    
        if (!exists.booleanValue()) {
            return null;
        }
    
        return new RedisCacheElement(cacheKey, fromStoreValue(lookup(cacheKey)));
    }
    
    protected Object lookup(Object key) {
    
        RedisCacheKey cacheKey = key instanceof RedisCacheKey ? (RedisCacheKey) key : getRedisCacheKey(key);
    
        byte[] bytes = (byte[]) redisOperations.execute(new AbstractRedisCacheCallback<byte[]>(
                new BinaryRedisCacheElement(new RedisCacheElement(cacheKey, null), cacheValueAccessor), cacheMetadata) {
    
            @Override
            public byte[] doInRedis(BinaryRedisCacheElement element, RedisConnection connection) throws DataAccessException {
                return connection.get(element.getKeyBytes());
            }
        });
    
        return bytes == null ? null : cacheValueAccessor.deserializeIfNecessary(bytes);
    }

### 解决方案 ###

更换版本：spring-data-redis在1.8.11的版本中修复了该问题

<dependency>
        <groupId>org.springframework.data</groupId>
        <artifactId>spring-data-redis</artifactId>
        <version>1.8.11.RELEASE</version>
    </dependency>

1.8.11的源代码:

public RedisCacheElement get(final RedisCacheKey cacheKey) {
    
        Assert.notNull(cacheKey, "CacheKey must not be null!");
    
        Boolean exists = (Boolean) redisOperations.execute(new RedisCallback<Boolean>() {
    
            @Override
            public Boolean doInRedis(RedisConnection connection) throws DataAccessException {
                return connection.exists(cacheKey.getKeyBytes());
            }
        });
    
        if (!exists) {
            return null;
        }
    
        byte[] bytes = doLookup(cacheKey);
    
        // safeguard if key gets deleted between EXISTS and GET calls.
        if (bytes == null) {
            return null;
        }
    
        return new RedisCacheElement(cacheKey, fromStoreValue(deserialize(bytes)));
    }
    
    private byte[] doLookup(Object key) {
    
        RedisCacheKey cacheKey = key instanceof RedisCacheKey ? (RedisCacheKey) key : getRedisCacheKey(key);
    
        return (byte[]) redisOperations.execute(new AbstractRedisCacheCallback<byte[]>(
                new BinaryRedisCacheElement(new RedisCacheElement(cacheKey, null), cacheValueAccessor), cacheMetadata) {
    
            @Override
            public byte[] doInRedis(BinaryRedisCacheElement element, RedisConnection connection) throws DataAccessException {
                return connection.get(element.getKeyBytes());
            }
        });
    }

### 配置Redis管理器 ###

@Configuration
    public class RedisConfig { 
    
        /** * ehcache默认过期时间 * @param redisTemplate * @return */
        @Bean
        public CacheManager cacheManager(RedisTemplate<String,?> redisTemplate) {
            RedisCacheManager cacheManager= new RedisCacheManager(redisTemplate);
            // 开启使用缓存名称最为key前缀
            cacheManager.setUsePrefix(true);
            cacheManager.setDefaultExpiration(60);
            return cacheManager;
        }
    
    }