custom-serializers.md

Custom serializers

kspoon supports custom HTML serializers by exposing public KspoonDecoder that can be used to obtain Ksoup classes (Element, Elements and Document). This allows to extract HTML elements and attributes that are not supported directly by kspoon (for example comments or tag names).

Here is an example of a custom serializer that extracts the tag name of the selected element:

object TagSerializer : KSerializer<String> {
    override val descriptor: SerialDescriptor =
        PrimitiveSerialDescriptor("TagString", PrimitiveKind.STRING)

    override fun deserialize(decoder: Decoder): String {
        val kspoonDecoder = decoder as KspoonDecoder
        val element = decoder.decodeElement()
        val tag = element?.tag()?.name
            ?: throw KspoonParseException("Could not get tag name for selector: ${kspoonDecoder.getSelectorFullPath()}")
        return tag
    }

    override fun serialize(encoder: Encoder, value: String) {
        throw KspoonParseException("Serialization is not supported")
    }
}

or to get comments:

object CommentsSerializer : KSerializer<List<String>> {
    override val descriptor: SerialDescriptor =
        PrimitiveSerialDescriptor("CommentStringList", PrimitiveKind.STRING)

    override fun deserialize(decoder: Decoder): List<String> {
        val kspoonDecoder = decoder as KspoonDecoder
        val element = decoder.decodeElementOrThrow()
        return element.nodeStream().filterIsInstance<Comment>().map { it.data }.toList()
    }

    override fun serialize(encoder: Encoder, value: String) {
        throw KspoonParseException("Serialization is not supported")
    }
}