A modern programming language that makes developers happier.

kotlinlang

Hello all. I'm using the lib, `jackson-module-kotlin,` to serialize but I'm having an error:

Sem título

I have the following methods, to serilize to JsonNode and deserialize.

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')```

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;`  ?

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

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?

<https://github.com/FasterXML/jackson-docs/wiki/JacksonPolymorphicDeserialization>

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

sth like
```jacksonObjectMapper().readValue("{}", jacksonTypeRef&lt;Event&lt;Consumer&gt;&gt;())```


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

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

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

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

Thank you <@U8F19U0TD>, <@UFSJBM7UN>. I will read about it and try to implement it.