Is it possible to use kotlinx-datetime with Gson

Question

I have JSON data which is retrieved from the local realm database. I'm trying to convert it into the corresponding data class. I have an ISO date field

{
  ....
  "createdAt" : "2022-05-04T10:16:56.489Z"
  ....

}

What I'm trying to do is to convert this string date field into kotlinx-datetime's Instant object which is a serializable class. Thus I made my data class as

import kotlinx.datetime.Instant

data class PollPinComment(
    ...
    val createdAt: Instant? = null,
    ...
)

Which doesn't work and gives an error as follows

com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 288 path $[0].createdAt

I'm sure that I might need to write some serialization/deserialization logic with gson to convert this string into Instant object. So my question is how can I do that? Thanks in advance

Answer 1

You can create a custom Deserializer for this and register it as type adapter to your Gson object.

class InstantDateDeserializer: JsonDeserializer<Instant> {
    override fun deserialize(
        json: JsonElement?, 
        typeOfT: Type?, 
        context: JsonDeserializationContext?
    ): Instant? {
        return json?.asString?.let {
            Instant.parse(it)
        }
    }
}

Create Gson() object pasing that deserializer as type adapter

val gson: Gson = GsonBuilder ()
    .registerTypeAdapter(Instant::class.java, InstantDateDeserializer())
    .create()

---

If you are using it with Retrofit

In Retrofit builder pass this to GsonConverterFactory

val retrofit = Retrofit.Builder()
    .baseUrl(BASE_URL)
    .addConverterFactory(GsonConverterFactory.create(gson))
    .build()

Answer 2

GSON parses only basic data types, such as Int, String, double... Other classes that need to be parsed must also consist of these basic data types. could do like this:

 data class PollPinComment(val createdAt: String ){

 fun  getCreatedAt(): Instant{
     return  Instant.parse(createdAt) 
 }
 }