Hello all I m using the lib `jackson module kotlin ` to seri

Question

Hello all I m using the lib `jackson module kotlin ` to serialize but I m having an error

Rodrigo Silva · Answer

I have the following methods to serilize to JsonNode and deserialize

Rodrigo Silva · Answer

Deserializing a class

Rodrigo Silva · Answer

But I always get the following error ```java lang ClassCastException class java util LinkedHashMap cannot be cast to class com rjdesenvolvimento aries access consumer consumer Consumer java util LinkedHashMap is in module java base of loader bootstrap com rjdesenvolvimento aries access consumer consumer Consumer is in unnamed module of loader app ```

Rodrigo Silva · Answer

Could anyone help

araqnid · Answer

My guess is that you have to tell Jackson what the T type is when deserializing if you don t it assumes T is Any and just uses the default serialization which will convert a JSON object into a LinkedHashMap Are you expecting an `Event lt Consumer gt `

araqnid · Answer

You tell it what type T is by passing a TypeReference the Kotlin module has a helper function to create one called `jacksonTypeRef `

Rodrigo Silva · Answer

Yes I m waiting for `Event lt Consumer gt ` But I also expect other classes like `Event lt Person gt ` `Event lt Address gt ` How do I solve this problem

Joe · Answer

Joe · Answer

one way to go about it is to serialize a type property that jackson can key off of when deserializing based on polymorphic type annotations

araqnid · Answer

sth like ```jacksonObjectMapper readValue jacksonTypeRef lt Event lt Consumer gt gt ```

Joe · Answer

<https github com trib3 leakycauldron blob master graphql src main kotlin com trib3 graphql websocket GraphQLWebSocketProtocol kt> has a working example

araqnid · Answer

yes the polymorphic deserialisation works too provided the JSON has a clear indication which type is there

araqnid · Answer

if that type is more from context it might be easier to specify the type when reading

Joe · Answer

agreed if you know what you re going to get then Steve s way is easier to understand what s going on if you re listening for messages and don t know the order they ll arrive in then the JSON needs some way to tell which type is being read

Rodrigo Silva · Answer

Thank you < araqnid> < Joe> I will read about it and try to implement it