Convert string data representation back to Kotlin Data Class

In Kotlin how is possible to convert a data class from its string representation back to the actual data class without having to manually parse the string?

for example, I have the next data class where both Interest and EmploymentType are enums, being the second element a List.

data class DataFilter(val mainInterest: Interest, val employments: List<EmploymentType>)

with toString I can get the contents its string representation, but if I want to get it back to a data class, how is it done?

Solution

For this purpose, you need to use a serialization library. I recommend you use Kotlinx.serialization library. This will help you convert the data object into a JSON String and convert it back to the data object easily.

You can follow the guideline to setup Kotlinx.serialization library.

After the setup is done, look at the following example: I will define both enum classes Interest and EmploymentType, and the DataFilter class:

import kotlinx.serialization.Serializable
import kotlinx.serialization.decodeFromString
import kotlinx.serialization.encodeToString
import kotlinx.serialization.json.Json

enum class Interest {
    SPORTS,
    BOOKS,
    TRAVEL,
    FOOD,
    TECHNOLOGY,
    ART,
    OTHER
}

enum class EmploymentType {
    FULL_TIME,
    PART_TIME,
    CONTRACT,
    FREELANCE,
    OTHER
}

@Serializable //You have to annotate your class as Serializable to make it works.
data class DataFilter(
    val mainInterest: Interest,
    val employment: List<EmploymentType>
)

Notice that Interest and EmploymentType are not annotated as @Serializable because enums are Serializable by default, but if you defined any other normal classes to use with DataFilter, then you have to annotate them as well.

Next, I will show you how conversions work:

fun main() {
    val filter = DataFilter(
        mainInterest = Interest.BOOKS,
        employment = listOf(EmploymentType.FULL_TIME, EmploymentType.FREELANCE)
    )

// Converting filter object into JSON String:
    val filterAsJsonString = Json.encodeToString(filter)
    println(filterAsJsonString) //prints {"mainInterest":"BOOKS","employment":["FULL_TIME","FREELANCE"]}

//Convert JSON String back to data object:
    val filterAsDataObject: DataFilter = Json.decodeFromString(filterAsJsonString)
    println(filterAsDataObject) //prints DataFilter(mainInterest=BOOKS, employment=[FULL_TIME, FREELANCE])
}