Why does Spring #Cacheable not pass the annotated method's result type to its deserializer? - spring

Question

This is sample code with Kotlin.
#Configuration
#Bean("cacheManager1hour")
fun cacheManager1hour(#Qualifier("cacheConfig") cacheConfiguration: RedisCacheConfiguration, redisConnectionFactory: RedisConnectionFactory): CacheManager {
cacheConfiguration.entryTtl(Duration.ofSeconds(60 * 60))
return RedisCacheManager.builder(redisConnectionFactory)
.cacheDefaults(cacheConfiguration)
.build()
}
#Bean("cacheConfig")
fun cacheConfig(objectMapper:ObjectMapper): RedisCacheConfiguration {
return RedisCacheConfiguration.defaultCacheConfig()
.computePrefixWith { cacheName -> "yaya:$cacheName:" }
.serializeKeysWith(RedisSerializationContext.SerializationPair.fromSerializer(StringRedisSerializer()))
.serializeValuesWith(RedisSerializationContext.SerializationPair.fromSerializer(GenericJackson2JsonRedisSerializer()))
}
#RestController
#Cacheable(value = "book", key = "#root.methodName", cacheManager = "cacheManager1hour")
fun getBook(): Book {
return Book()
}
class Book {
var asdasd:String? = "TEST"
var expires_in = 123
}
The GenericJackson2JsonRedisSerializer cannot process the "kotlin class" and we need to add '#class as property' to the Redis cache entry.
Anyway, why do we need the #class? The Spring context is aware of the result's type, why doesn't it get passed? We would have two benefits:
less memory
easy for the Serializer, i.e. objectMapper.readValue(str, T)
Annotated Spring code for illustration
// org.springframework.cache.interceptor.CacheAspectSupport
#Nullable
private Cache.ValueWrapper findInCaches(CacheOperationContext context, Object key) {
for (Cache cache : context.getCaches()) {
// --> maybe we can pass the context.method.returnType to doGet
Cache.ValueWrapper wrapper = doGet(cache, key);
if (wrapper != null) {
if (logger.isTraceEnabled()) {
logger.trace("Cache entry for key '" + key + "' found in cache '" +
cache.getName() + "'");
}
return wrapper;
}
}
return null;
}
// org.springframework.data.redis.cache.RedisCache
#Override
protected Object lookup(Object key) {
// -> there will get the deserialized type can pass to Jackson
byte[] value = cacheWriter.get(name, createAndConvertCacheKey(key));
if (value == null) {
return null;
}
return deserializeCacheValue(value);
}

Answer 1

Your return type could be:
some abstract class
some interface
In those cases your return type is almost useless to deserialize the object. Encoding the actual class always works .