What is the reason why the return value is empty when using RedisTemplate for batch query? How to solve this problem?

This article analyzes the reason why the return value is empty when using Spring Data Redis's RedisTemplate for batch query, and provides corresponding solutions. When using the executePipelined method for batch GET operation, if the result is processed directly inside the pipeline, the return value will be empty. This is because the pipeline operation will cache all commands and will not be sent to the Redis server until executePipelined is called, and internal processing cannot obtain timely returns.

Question description:

Two error examples are given in the article, both of which try to process the results of the GET command inside executePipelined , resulting in the final returned list being all null .

Problem analysis and solutions:

The core of the problem lies in the asynchronous characteristics of pipeline operations. The correct approach should be performed after executePipelined method returns the result and then uniformly handled. The first method provided in this article deserializes within a loop, which destroys the efficiency of pipeline operations. Although the second method uses SessionCallback , it still performs result processing inside the pipeline.

Improved solutions:

An improved batchGetList method is provided in the article, which correctly utilizes the return value of executePipelined :

 public<t> List<t> batchGetList(Collection<string> keys) {
    if (CollectionUtil.isEmpty(keys)) {
        return new ArrayList();
    }

    List<object> results = redisTemplate.executePipelined((RedisConnection connection) -> {
        RedisSerializer<string> keySerializer = (RedisSerializer<string> ) redisTemplate.getKeySerializer();
        for (String key : keys) {
            connection.get(keySerializer.serialize(key));
        }
        return null;
    });

    // Execute external processing results in the pipeline return results.stream()
                  .map(result -> (T) redisTemplate.getValueSerializer().deserialize((byte[]) result))
                  .collect(Collectors.toList());
}</string></string></object></string></t></t>

This method first checks whether keys are empty, and then uses executePipelined to perform batch GET operations. The key is that after the pipeline execution is finished, it uses Stream API to traverse results list and deserialize each result using redisTemplate.getValueSerializer().deserialize method, eventually returning a list with the correct data. This avoids the wrong practice of processing results inside the pipeline and ensures that the data in Redis is properly retrieved. It should be noted that this method assumes that all key-value pairs use the same deserializer. If there are multiple data types, it needs to be adjusted according to actual conditions.

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