Replace gson with kotlin serialization (#209)

* replace gson with kotlin serialization

* Remove unused plugin

* Fix missing library reference

* Remove unused json library

---------

Co-authored-by: Fabian Keunecke <f@biankeunecke.de>

Author: twolf-zolitron

app/build.gradle.kts

@@ -1,6 +1,7 @@
 plugins {
     alias(libs.plugins.android.application)
     alias(libs.plugins.kotlin.android)
+    alias(libs.plugins.kotlinx.serialization)
 }
 
 apply {
@@ -88,6 +89,9 @@ dependencies {
     // Logging
     implementation(libs.timber)
 
+    // Serialization
+    implementation(libs.kotlinx.serialization.json)
+
     // Leak Canary
     implementation(libs.leakcanary)
 

app/src/main/java/org/maplibre/navigation/android/example/GraphHopperNavigationActivity.kt

@@ -5,7 +5,7 @@ import android.os.Bundle
 import android.view.View
 import androidx.appcompat.app.AppCompatActivity
 import com.google.android.material.snackbar.Snackbar
-import com.google.gson.Gson
+import kotlinx.serialization.json.*
 import org.maplibre.geojson.model.Point
 import org.maplibre.android.annotations.MarkerOptions
 import org.maplibre.android.camera.CameraPosition
@@ -171,17 +171,21 @@ class GraphHopperNavigationActivity :
 
         // The full GraphHopper API is documented here:
         // https://docs.graphhopper.com/openapi/routing
-        val requestBody = mapOf(
-            "type" to "mapbox",
-            "profile" to "car",
-            "locale" to language,
-            "points" to listOf(
-                listOf(origin.longitude, origin.latitude),
-                listOf(destination.longitude, destination.latitude)
-            )
-        )
-
-        val requestBodyJson = Gson().toJson(requestBody)
+        val requestBodyJson = buildJsonObject {
+            put("type", "mapbox")
+            put("profile", "car")
+            put("locale", language)
+            putJsonArray("points") {
+                addJsonArray {
+                    add(origin.longitude)
+                    add(origin.latitude)
+                }
+                addJsonArray {
+                    add(destination.longitude)
+                    add(destination.latitude)
+                }
+            }
+        }.toString()
         val client = OkHttpClient()
 
         // Create request object. Requires graphhopper_url to be set in developer-config.xml

app/src/main/java/org/maplibre/navigation/android/example/ValhallaNavigationActivity.kt

@@ -5,7 +5,7 @@ import android.os.Bundle
 import android.view.View
 import androidx.appcompat.app.AppCompatActivity
 import com.google.android.material.snackbar.Snackbar
-import com.google.gson.Gson
+import kotlinx.serialization.json.*
 import org.maplibre.geojson.Point
 import org.maplibre.android.annotations.MarkerOptions
 import org.maplibre.android.camera.CameraPosition
@@ -180,35 +180,33 @@ class ValhallaNavigationActivity :
         // That would allow us to skip adding fake attributes further down as well.
         // But this is the first step to show how the newly added banner_instructions
         // and voice_instructions of Valhalla can be used to generate directions directly:
-        val requestBody = mapOf(
-            "format" to "osrm",
-            "costing" to "auto",
-            "banner_instructions" to true,
-            "voice_instructions" to true,
-            "language" to language,
-            "directions_options" to mapOf(
-                "units" to "kilometers"
-            ),
-            "costing_options" to mapOf(
-                "auto" to mapOf(
-                    "top_speed" to 130
-                )
-            ),
-            "locations" to listOf(
-                mapOf(
-                    "lon" to origin.longitude(),
-                    "lat" to origin.latitude(),
-                    "type" to "break"
-                ),
-                mapOf(
-                    "lon" to destination.longitude(),
-                    "lat" to destination.latitude(),
-                    "type" to "break"
-                )
-            )
-        )
-
-        val requestBodyJson = Gson().toJson(requestBody)
+        val requestBodyJson = buildJsonObject {
+            put("format", "osrm")
+            put("costing", "auto")
+            put("banner_instructions", true)
+            put("voice_instructions", true)
+            put("language", language)
+            putJsonObject("directions_options") {
+                put("units", "kilometers")
+            }
+            putJsonObject("costing_options") {
+                putJsonObject("auto") {
+                    put("top_speed", 130)
+                }
+            }
+            putJsonArray("locations") {
+                addJsonObject {
+                    put("lon", origin.longitude())
+                    put("lat", origin.latitude())
+                    put("type", "break")
+                }
+                addJsonObject {
+                    put("lon", destination.longitude())
+                    put("lat", destination.latitude())
+                    put("type", "break")
+                }
+            }
+        }.toString()
         val client = OkHttpClient()
 
         // Create request object. Requires valhalla_url to be set in developer-config.xml

gradle/libs.versions.toml

@@ -21,7 +21,6 @@ androidx-cardview = "1.0.0"
 androidx-lifecycle-viewmodel = "2.10.0"
 androidx-multidex = "2.0.1"
 picasso = "2.71828"
-json = "20250517"
 timber = "5.0.1"
 autovalue = "1.11.1"
 mapbox-geojson = "5.8.0"
@@ -62,7 +61,6 @@ autovalue = { group = "com.google.auto.value", name = "auto-value", version.ref
 autovalue-annotations = { group = "com.google.auto.value", name = "auto-value-annotations", version.ref = "autovalue" }
 picasso = { group = "com.squareup.picasso", name = "picasso", version.ref = "picasso" }
 timber = { group = "com.jakewharton.timber", name = "timber", version.ref = "timber" }
-json = { group = "org.json", name = "json", version.ref = "json" }
 leakcanary = { group = "com.squareup.leakcanary", name = "leakcanary-android", version.ref = "leakcanary" }
 
 # Test KMP

libandroid-navigation-ui/build.gradle.kts

@@ -105,7 +105,6 @@ dependencies {
     testImplementation(libs.junit)
     testImplementation(libs.mockito)
     testImplementation(libs.robolectric)
-    testImplementation(libs.json)
     testImplementation(libs.mockk)
 }
 

libandroid-navigation-ui/src/main/java/org/maplibre/navigation/android/navigation/ui/v5/NavigationLauncher.java

@@ -6,8 +6,6 @@
 import android.content.SharedPreferences;
 import android.preference.PreferenceManager;
 
-import com.google.gson.Gson;
-
 import org.maplibre.navigation.android.navigation.ui.v5.route.NavigationRoute;
 import org.maplibre.navigation.core.models.DirectionsRoute;
 import org.maplibre.navigation.core.navigation.NavigationConstants;
@@ -53,7 +51,7 @@ public static void startNavigation(Context context, NavigationLauncherOptions op
    * Used to extract the route used to launch the drop-in UI.
    * <p>
    * Extracts the route {@link String} from {@link SharedPreferences} and converts
-   * it back to a {@link DirectionsRoute} object with {@link Gson}.
+   * it back to a {@link DirectionsRoute} object.
    *
    * @param context to retrieve {@link SharedPreferences}
    * @return {@link DirectionsRoute} stored when launching

sample/android/app/build.gradle.kts

@@ -52,6 +52,7 @@ dependencies {
     implementation(libs.maplibre.navigation.core)
     implementation(libs.maplibre.geojson)
 
+    implementation(libs.kotlinx.serialization.json)
     implementation(libs.okhttp)
     implementation(libs.androidx.core.ktx)
     implementation(libs.androidx.appcompat)

sample/android/app/src/main/java/org/maplibre/navigation/sample/android/core/CoreOnlyFragment.kt

@@ -10,7 +10,7 @@ import androidx.core.view.ViewCompat
 import androidx.core.view.WindowInsetsCompat
 import androidx.fragment.app.Fragment
 import androidx.lifecycle.lifecycleScope
-import com.google.gson.Gson
+import kotlinx.serialization.json.*
 import kotlinx.coroutines.launch
 import okhttp3.Call
 import okhttp3.MediaType.Companion.toMediaType
@@ -148,53 +148,56 @@ class CoreOnlyFragment : Fragment() {
 
     private suspend fun fetchRoute(): DirectionsResponse = suspendCoroutine { continuation ->
         val provider = "valhalla"
-
-        val requestBody = if (provider == "graphhopper") {
-            mapOf(
-                "type" to "mapbox",
-                "profile" to "car",
-                "locale" to "en-US",
-                "points" to listOf(
+        val requestBodyJson = if (provider == "graphhopper") {
+            buildJsonObject {
+                put("type", "mapbox")
+                put("profile", "car")
+                put("locale", "en-US")
+                putJsonArray("points") {
                     // Hannover, Germany
-                    listOf(9.6935451, 52.3758408),
+                    addJsonArray {
+                        add(9.6935451)
+                        add(52.3758408)
+                    }
                     // Hamburg, Germany
-                    listOf(9.9769191, 53.5426183)
-                )
+                    addJsonArray {
+                        add(9.9769191)
+                        add(53.5426183)
+                    }
+                }
                 // flexible options possible via "custom_model"
-            )
+            }.toString()
         } else {
-            mapOf(
-                "format" to "osrm",
-                "costing" to "auto",
-                "banner_instructions" to true,
-                "voice_instructions" to true,
-                "language" to "en-US",
-                "directions_options" to mapOf(
-                    "units" to "kilometers"
-                ),
-                "costing_options" to mapOf(
-                    "auto" to mapOf(
-                        "top_speed" to 130
-                    )
-                ),
-                "locations" to listOf(
+            buildJsonObject {
+                put("format", "osrm")
+                put("costing", "auto")
+                put("banner_instructions", true)
+                put("voice_instructions", true)
+                put("language", "en-US")
+                putJsonObject("directions_options") {
+                    put("units", "kilometers")
+                }
+                putJsonObject("costing_options") {
+                    putJsonObject("auto") {
+                        put("top_speed", 130)
+                    }
+                }
+                putJsonArray("locations") {
                     // Hannover, Germany
-                    mapOf(
-                        "lon" to 9.6935451,
-                        "lat" to 52.3758408,
-                        "type" to "break"
-                    ),
+                    addJsonObject {
+                        put("lon", 9.6935451)
+                        put("lat", 52.3758408)
+                        put("type", "break")
+                    }
                     // Hamburg, Germany
-                    mapOf(
-                        "lon" to 9.9769191,
-                        "lat" to 53.5426183,
-                        "type" to "break"
-                    )
-                )
-            )
+                    addJsonObject {
+                        put("lon", 9.9769191)
+                        put("lat", 53.5426183)
+                        put("type", "break")
+                    }
+                }
+            }.toString()
         }
-
-        val requestBodyJson = Gson().toJson(requestBody)
         val client = OkHttpClient()
 
         val url = if (provider == "valhalla") "https://valhalla1.openstreetmap.de/route"

sample/android/gradle/libs.versions.toml

@@ -6,6 +6,8 @@ maplibre = "11.6.1"
 maplibre-geojson = "343269b2"
 maplibre-navigation = "411fb14c"
 
+kotlinx-serialization-json = "1.9.0"
+
 coreKtx = "1.15.0"
 junit = "4.13.2"
 junitVersion = "1.2.1"
@@ -24,6 +26,7 @@ androidx-appcompat = { group = "androidx.appcompat", name = "appcompat", version
 material = { group = "com.google.android.material", name = "material", version.ref = "material" }
 androidx-activity = { group = "androidx.activity", name = "activity", version.ref = "activity" }
 androidx-constraintlayout = { group = "androidx.constraintlayout", name = "constraintlayout", version.ref = "constraintlayout" }
+kotlinx-serialization-json = { group = "org.jetbrains.kotlinx", name = "kotlinx-serialization-json", version.ref = "kotlinx-serialization-json" }
 
 okhttp =  { group = "com.squareup.okhttp3", name ="okhttp", version = "4.12.0" }