# Using kotlinx.serialization instead of gson

**URL:** <https://openrndr.discourse.group/t/using-kotlinx-serialization-instead-of-gson/725>\
**Category:** Tutorials\
**Created:** [December 30, 2024, 11:26am UTC](https://openrndr.discourse.group/t/using-kotlinx-serialization-instead-of-gson/725 "2024-12-30T11:26:41Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![abe](https://yyz2.discourse-cdn.com/free1/user_avatar/openrndr.discourse.group/abe/32/700_2.png) [@abe](https://openrndr.discourse.group/u/abe)\
**Post date:** [December 30, 2024, 11:26am UTC](https://openrndr.discourse.group/t/using-kotlinx-serialization-instead-of-gson/725/1 "2024-12-30T11:26:41Z")

</div>

In the `latest` branch of `openrndr-template` we have switched from `gson` to `kotlinx-serialization`.

What both of these libraries do is making it easy to save and load program state. Gson comes from Google and kotlinx-serialization from the developers of Kotlin.  
The syntax when using the second one is a bit less verbose.

Here the official introduction:

> **[Serialization | Kotlin](https://kotlinlang.org/docs/serialization.html)**

If you want to add kotlinx-serialization it to your openrndr-template based program, take a look at the required changes in this commit:

> <https://github.com/openrndr/openrndr-template/commit/e4dfb4aaed81b38100f5ca6aac06e1c482e75a78>

I’m copying here the notes from that commit:

# Save JSON (before)

```auto
val gson = Gson()
val json = gson.toJson(points)
File(path).writeText(json)

```

# Save JSON (new syntax)

```auto
val json = Json.encodeToString(points)
File(path).writeText(json)

```

if `points` is a `List` of `Point`, and `Point` is `@Serializable`

# Load JSON (before)

```auto
val gson = Gson()
val typeToken = object : TypeToken<List<Point>>() {}
val json = File(path).readText()
val points: List<Point> = gson.fromJson(json, typeToken.type)

```

# Load JSON (new syntax)

```auto
val json = File(path).readText()
val poinsts = Json.decodeFromString<List<Point>>(json)

```

## Use these imports with the new syntax

```auto
import kotlinx.serialization.Serializable
import kotlinx.serialization.Transient
import kotlinx.serialization.encodeToString
import kotlinx.serialization.json.Json

```

OPENRNDR classes are already annotated as [@Serializable](https://github.com/openrndr/openrndr/blob/master/openrndr-math/src/commonMain/kotlin/org/openrndr/math/Vector2.kt#L13) so that’s taken care of. If you want to serialize your own classes, you need to annotate them. For example:

```kotlin
import kotlinx.serialization.Serializable
import kotlinx.serialization.Transient
...

@Serializable
data class Point(
    var position: Vector2,
    var radius: Double,
    var completeness: Double = 1.0,
    var rotation: Double = 0.0
) {
    @Transient
    var contour: ShapeContour? = null

    init {
        ...
    }
    ....

```

You can mark as `@Transient` members that do not need serialized. In this example, `contour` is generated out of `position`, `radius`, `completeness` and `rotation`, so there’s no need to save the `contour` to the JSON file, which would make it heavier and less readable. I simply reconstruct that contour inside `init`, or any time one of the four properties of Point are changed. The `init` method is called when you deserialize (load a JSON file to construct object instances).

With these annotations, one could easily load and save a list of `Point` with functions like these:

```kotlin
fun saveJson(points: MutableList<Point>) {
    File(pointsPath).writeText(Json.encodeToString(points))
    println("saved")
}

fun loadJson(): MutableList<Point> {
    return if(File(pointsPath).exists()) {
        val json = File(pointsPath).readText()
        println("loaded")
        Json.decodeFromString<MutableList<Point>>(json)
    } else mutableListOf()
}

```