Hi everyone, I'm consuming data from a JSON API. Some responses contain decimal numbers. Depending ...

# serialization

[Tiago Nunes]

Hi everyone,

I'm consuming data from a JSON API. Some responses contain decimal numbers. Depending in the culture-info field sent to the server, they might use dots (e.g. 18.312) or commas (e.g. 18,312)

Is there some way I can interpret these both as Float in my Serializer class (Float only accepts dot notation)? Maybe through some custom field desserialization or something...?

[Javier]

you can create a custom serializer for example

[Tiago Nunes]

A custom serializer can receive a String and return a Float? How would I use it after creating it?

[Tiago Nunes]

Can a custom serializer for certain fields only?

[Tiago Nunes]

Oh I think i get it, I create a custom serializer, then I create a Serializable class CustomFloat with that serializer, and the fields will be of that type,right?

[Javier]

https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/serializers.md#primitive-serializer

[Javier]

Here you have a lot of examples

[Javier]

I would use a specific class for that

[Javier]

Do you need to handle that float in local?

[Javier]

Or you are only going to show that string in the UI?

[Tiago Nunes]

No, I'm not showing that string in the UI. I rather have it saved only as a Float and deal with Internationalization locally

[Javier]

then if it is a "real" float, I would create a custom class for that, but ideally backend should solve that

[Tiago Nunes]

Yeah but changing the backend is not an option, what you gona do 🥲

[Tiago Nunes]

@Javier

I have this

object FloatAsDecimalString : KSerializer<Float> {
    override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("Float", PrimitiveKind.STRING)

    override fun serialize(encoder: Encoder, value: Float) =
        encoder.encodeString(value.toString())

    override fun deserialize(decoder: Decoder): Float =
        decoder.decodeString().replace(",", ".").toFloat()
}

@Serializable
data class ExampleResponse(
    val id: Long,
    val someDecimal: Float,
)

Now, how do I apply the Serializer?

[Javier]

@Serializable
data class ExampleResponse(
    val id: Long,
    @Serializable(with = FloatAsDecimalString::class) val someDecimal: Float,
)

[Javier]

I think with that

[Tiago Nunes]

Json.decodeFromString<ExampleResponse>("""
    {
        "id": 1,
        "someDecimal": "1.31"
    }
""")

This gave me an error:

java.lang.ExceptionInInitializerError
at com.qmx.web.contract.response.ExampleResponse$$serializer.deserialize(Unknown Source:64)
at com.qmx.web.contract.response.ExampleResponse$$serializer.deserialize(ExampleResponse.kt:24)
at kotlinx.serialization.json.internal.PolymorphicKt.decodeSerializableValuePolymorphic(Polymorphic.kt:63)
at kotlinx.serialization.json.internal.StreamingJsonDecoder.decodeSerializableValue(StreamingJsonDecoder.kt:33)
at kotlinx.serialization.json.Json.decodeFromString(Json.kt:85)

[Javier]

this is working for me

[Javier]

I changed the Float inside PrimitiveSerialDecriptor

[Tiago Nunes]

Why?

[Tiago Nunes]

Wow it worked for me too changing to "id"

[Tiago Nunes]

But why hahaha

[Javier]

I think because you cant use a type

[Javier]

you can change that to whatever you want, sasdsadas should work too

[Tiago Nunes]

There's probably a better descriptor for this use case then maybe? I don't know anything about descriptors yet...

[Javier]

probably that Serial name will create some code under the hood, and using Float or whatever existent type or reserved words is not a good idea

[Javier]

I usually put the original property name, in this case I would put someDecimal,

[Tiago Nunes]

I'll put DecimalString. I think it makes sense, its a DecimalString, which is a String, that's the description of the field i guess hahaha

[Tiago Nunes]

Anyway, thanks a lot 🙌