How are cache misses handled by spring-data-redis multiGet? - spring-boot

Question

I am using a Redis cache (via the Jedis client), and I would like to use ValueOperations#multiGet, which takes a Collection of keys, and returns a List of objects from the cache, in the same order. My question is, what happens when some of the keys are in the cache, but others are not? I am aware that underneath, Redis MGET is used, which will return nil for any elements that are not in the cache.
I cannot find any documentation of how ValueOperations will interpret this response. I assume they will be null, and can certainly test it, but it would be dangerous to build a system around undocumented behavior.
For completeness, here is how the cache client is configured:
#Bean
public RedisConnectionFactory redisConnectionFactory() {
JedisConnectionFactory redisConnectionFactory = new JedisConnectionFactory();
redisConnectionFactory.setHostName(address);
redisConnectionFactory.setPort(port);
redisConnectionFactory.afterPropertiesSet();
return redisConnectionFactory;
}
#Bean
public ValueOperations<String, Object> someRedisCache(RedisConnectionFactory cf) {
RedisTemplate<String, Object> redisTemplate = new RedisTemplate<>();
redisTemplate.setConnectionFactory(cf);
redisTemplate.setDefaultSerializer(new GenericJackson2JsonRedisSerializer());
redisTemplate.afterPropertiesSet();
return redisTemplate.opsForValue();
}
I am using spring-data-redis:2.1.4
So, is there any documentation around this, or some reliable source of truth?

Answer 1

After some poking around, it looks like the answer has something to do with the serializer used - in this case GenericJackson2JsonRedisSerializer. Not wanting to dig too much, I simply wrote a test validating that any (nil) values returned by Redis are convereted to null:
#Autowired
ValueOperations<String, SomeObject> valueOperations
#Test
void multiGet() {
//Given
SomeObject someObject = SomeObject
.builder()
.contentId("key1")
.build()
valueOperations.set("key1", someObject)
//When
List<SomeObject> someObjects = valueOperations.multiGet(Arrays.asList("key1", "nonexisting"))
//Then
assertEquals(2, someObjects.size())
assertEquals(someObject, someObjects.get(0))
assertEquals(null, someObjects.get(1))
}
So, in Redis, this:
127.0.0.1:6379> MGET "\"key1\"" "\"nonexisting\""
1) "{\"#class\":\"some.package.SomeObject\",\"contentId\":\"key1\"}"
2) (nil)
Will results in a List of {SomeObject, null}