Custom Kotlin Serializer for BigDecimal

Since BigDecimal is part of Java Math and not Kotlin, a custom serializer is needed if you’re not using Jackson. After some thought, I chose to serialize it into a string using KSerializer. This means that you will need to have kolinx.serialization installed. The following is the Kotlin code for the serializer.

import kotlinx.serialization.KSerializer
import kotlinx.serialization.descriptors.*
import kotlinx.serialization.encoding.Decoder
import kotlinx.serialization.encoding.Encoder
import java.math.BigDecimal

object BigDecimalSerializer: KSerializer<BigDecimal> {
    override fun deserialize(decoder: Decoder): BigDecimal {
        return decoder.decodeString().toBigDecimal()
    }

    override fun serialize(encoder: Encoder, value: BigDecimal) {
        encoder.encodeString(value.toPlainString())
    }

    override val descriptor: SerialDescriptor
        get() = PrimitiveSerialDescriptor("BigDecimal", PrimitiveKind.STRING)
}

It can be used in data classes like these:

@Serializable
data class Product(
    val id: Long,
    val name: String,
    val description: String,
    @Serializable(with = BigDecimalSerializer::class)
    val cost: BigDecimal,
)