springboot(20)Redis缓存@Cacheable对存在的数据返回null

springboot

问题描述

最近我们用Spring Cache + redis来做缓存，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：

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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

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<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:

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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

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@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;
	}
	
}
>