KotlinSerialization.kt

package io.github.jitinsharma

import kotlinx.serialization.*
import kotlinx.serialization.json.JSON

@Serializable
data class Destination(
        var name : String? = "",
        var country : String? = "",
        var code : Int = 0,
        @Optional
        var isMetro : Boolean = false,
        @Transient
        var favorite : Boolean = false
)

@Serializable
data class Country(var name : String = "", 
                   @SerialName("hemisphereCode")
                   var hCode : Int = -1) {

    @Serializer(forClass = Country::class)
    companion object : KSerializer<Country>{

        override fun load(input: KInput): Country {
            TODO("Write your own scheme to handle input")
        }

        override fun save(output: KOutput, obj: Country) {
            TODO("Write your own scheme to handle output")
        }

        override val serialClassDesc: KSerialClassDesc
            get() = TODO()
    }
}

class DestinationClass {

    companion object {
        fun findDestination() {
            val delhi = Destination(name = "Delhi", country = "India", code = 0)
            println(delhi)
            //Destination(name=New York, country=India, code=0, favorite=false)

            val delhiAsString = JSON.stringify(delhi)
            println(delhiAsString)
            //{"name":"Delhi","country":"India","code":0}

            val paris = JSON.unquoted.parse<Destination>(
                    "{name:Paris,country:France,code:10}")
            println(paris)
            //Destination(name=Paris, country=France, code=10, favorite=false)

            var barcelona = JSON.unquoted.parse<Destination>(
                    "{name:Barcelona,country:Spain,code:5}")
            println(barcelona)
            // Only optional and transient missing, so serialization works
            //Destination(name=Paris, country=France, code=10, isMetro=false, favorite=false)

            barcelona = JSON.unquoted.parse(
                    "{name:Barcelona,country:Spain,code:5,isMetro:true}")
            println(barcelona)
            //Destination(name=Barcelona, country=Spain, code=5, isMetro=true, favorite=false)
            //Optional property isMetro is updated but Transient property favorite remains same

            /*barcelona = JSON.unquoted.parse(
                    "{name:Barcelona,code:5,isMetro=true,favorite=true}")
            //This will break as "country" is a required field.*/

            val newYork = JSON.parse<Destination>(
                    "{\"name\":\"New York\",\"country\":\"USA\",\"code\":3}"
            )
            println(newYork)
            //Destination(name=New York, country=USA, code=3, favorite=false)

            val newYorkAsMap : Map<String,Any> = Mapper.map(newYork)
            val newnewYork = Mapper.unmap<Destination>(newYorkAsMap)
            println(newYorkAsMap)
            //{name=New York, country=USA, code=3}

            val newDelhi = CustomTransformer.transform(delhi)
            println(newDelhi)
        }

        object CustomTransformer : ValueTransformer() {

            override fun transformStringValue(desc: KSerialClassDesc, index: Int, value: String): String =
                    value.toLowerCase()

            override fun transformIntValue(desc: KSerialClassDesc, index: Int, value: Int): Int =
                    when(value) {
                        0 -> 1
                        else -> super.transformIntValue(desc, index, value)
                    }
        }
    }
}