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kotlinjacksonpolymorphismsubtypingsealed-class

Kotlin sealed class subtyping in Jackson

I have following classes:

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type")
@JsonSubTypes(
    JsonSubTypes.Type(value = Speech::class, name = "Speech"),
    JsonSubTypes.Type(value = Audio::class, name = "Audio"),
)
sealed class AudioItem

data class Speech(val type: String = "Speech", val contentType: String = "SSML", val content: String) : AudioItem()
data class Audio(val type: String = "Audio", val source: String) : AudioItem()

When I try to convert generic ArrayList:

ArrayList with items as LinkedHashMaps

to AudioItem

val audio: List<AudioItem> = ObjectMapper().findAndRegisterModules().convertValue(a)

I get:

Cannot construct instance of AudioItem (no Creators, like default constructor, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information

Solution

  • It should work when you use sealed class AudioItem() (mind the "()"). IntelliJ hints that we can delete "()" but if I do then I can't see any constructor in the "Structure" tab.

    Additionally, you don't need to explicitly set the type as in val type: String = "Speech". @JsonSubTypes will do that for you.