Rework expression conversion (#11490)

* [android] - rework expression conversion

26 files changed, 318 insertions, 157 deletions

diff --git a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/CircleLayer.java b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/CircleLayer.java
index 8f1c00f1b5..94929398d5 100644
--- a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/CircleLayer.java
+++ b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/CircleLayer.java
@@ -99,7 +99,7 @@ public class CircleLayer extends Layer {
   @Nullable
   public Expression getFilter() {
     Expression expression = null;
-    JsonArray array = nativeGetFilter();
+    JsonArray array = (JsonArray) nativeGetFilter();
     if (array != null) {
       expression = Expression.Converter.convert(array);
     }
diff --git a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/FillExtrusionLayer.java b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/FillExtrusionLayer.java
index 34f062b4d6..29e2b49d76 100644
--- a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/FillExtrusionLayer.java
+++ b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/FillExtrusionLayer.java
@@ -99,7 +99,7 @@ public class FillExtrusionLayer extends Layer {
   @Nullable
   public Expression getFilter() {
     Expression expression = null;
-    JsonArray array = nativeGetFilter();
+    JsonArray array = (JsonArray) nativeGetFilter();
     if (array != null) {
       expression = Expression.Converter.convert(array);
     }
diff --git a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/FillLayer.java b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/FillLayer.java
index 1865349c42..ed780811c0 100644
--- a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/FillLayer.java
+++ b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/FillLayer.java
@@ -99,7 +99,7 @@ public class FillLayer extends Layer {
   @Nullable
   public Expression getFilter() {
     Expression expression = null;
-    JsonArray array = nativeGetFilter();
+    JsonArray array = (JsonArray) nativeGetFilter();
     if (array != null) {
       expression = Expression.Converter.convert(array);
     }
diff --git a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/HeatmapLayer.java b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/HeatmapLayer.java
index a8d07bdbb4..42b4210710 100644
--- a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/HeatmapLayer.java
+++ b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/HeatmapLayer.java
@@ -99,7 +99,7 @@ public class HeatmapLayer extends Layer {
   @Nullable
   public Expression getFilter() {
     Expression expression = null;
-    JsonArray array = nativeGetFilter();
+    JsonArray array = (JsonArray) nativeGetFilter();
     if (array != null) {
       expression = Expression.Converter.convert(array);
     }
diff --git a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/Layer.java b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/Layer.java
index 26fc9d32e1..411fbe4435 100644
--- a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/Layer.java
+++ b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/Layer.java
@@ -3,6 +3,7 @@ package com.mapbox.mapboxsdk.style.layers;
 import android.support.annotation.NonNull;
 
 import com.google.gson.JsonArray;
+import com.google.gson.JsonElement;
 import com.mapbox.mapboxsdk.style.expressions.Expression;
 
 /**
@@ -72,7 +73,7 @@ public abstract class Layer {
 
   protected native void nativeSetFilter(Object[] filter);
 
-  protected native JsonArray nativeGetFilter();
+  protected native JsonElement nativeGetFilter();
 
   protected native void nativeSetSourceLayer(String sourceLayer);
 
diff --git a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/LineLayer.java b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/LineLayer.java
index 9dbd3aeb19..5e6e6d38e7 100644
--- a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/LineLayer.java
+++ b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/LineLayer.java
@@ -99,7 +99,7 @@ public class LineLayer extends Layer {
   @Nullable
   public Expression getFilter() {
     Expression expression = null;
-    JsonArray array = nativeGetFilter();
+    JsonArray array = (JsonArray) nativeGetFilter();
     if (array != null) {
       expression = Expression.Converter.convert(array);
     }
diff --git a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/SymbolLayer.java b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/SymbolLayer.java
index bc1e02a89f..6a2e131d7d 100644
--- a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/SymbolLayer.java
+++ b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/SymbolLayer.java
@@ -99,7 +99,7 @@ public class SymbolLayer extends Layer {
   @Nullable
   public Expression getFilter() {
     Expression expression = null;
-    JsonArray array = nativeGetFilter();
+    JsonArray array = (JsonArray) nativeGetFilter();
     if (array != null) {
       expression = Expression.Converter.convert(array);
     }
diff --git a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/layer.java.ejs b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/layer.java.ejs
index f3941aacf6..851a85f3d6 100644
--- a/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/layer.java.ejs
+++ b/platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/style/layers/layer.java.ejs
@@ -119,7 +119,7 @@ public class <%- camelize(type) %>Layer extends Layer {
   @Nullable
   public Expression getFilter() {
     Expression expression = null;
-    JsonArray array = nativeGetFilter();
+    JsonArray array = (JsonArray) nativeGetFilter();
     if (array != null) {
       expression = Expression.Converter.convert(array);
     }
diff --git a/platform/android/MapboxGLAndroidSDKTestApp/src/main/java/com/mapbox/mapboxsdk/testapp/activity/style/SymbolGeneratorActivity.java b/platform/android/MapboxGLAndroidSDKTestApp/src/main/java/com/mapbox/mapboxsdk/testapp/activity/style/SymbolGeneratorActivity.java
index c42f264478..f32aa5faf8 100644
--- a/platform/android/MapboxGLAndroidSDKTestApp/src/main/java/com/mapbox/mapboxsdk/testapp/activity/style/SymbolGeneratorActivity.java
+++ b/platform/android/MapboxGLAndroidSDKTestApp/src/main/java/com/mapbox/mapboxsdk/testapp/activity/style/SymbolGeneratorActivity.java
@@ -294,6 +294,13 @@ public class SymbolGeneratorActivity extends AppCompatActivity implements OnMapR
     Expression textFieldExpressionResult = symbolLayer.getTextField().getExpression();
     Expression textColorExpressionResult = symbolLayer.getTextColor().getExpression();
 
+    // log expressions
+    Timber.e(iconImageExpressionResult.toString());
+    Timber.e(iconSizeExpressionResult.toString());
+    Timber.e(textSizeExpressionResult.toString());
+    Timber.e(textFieldExpressionResult.toString());
+    Timber.e(textColorExpressionResult.toString());
+
     // reset expressions
     symbolLayer.setProperties(
       iconImage(iconImageExpressionResult),
diff --git a/platform/android/config.cmake b/platform/android/config.cmake
index 80d0810564..77074dc82c 100644
--- a/platform/android/config.cmake
+++ b/platform/android/config.cmake
@@ -131,7 +131,6 @@ add_library(mbgl-android STATIC
     platform/android/src/conversion/constant.hpp
     platform/android/src/conversion/conversion.hpp
     platform/android/src/style/conversion/function.hpp
-    platform/android/src/style/conversion/gson.hpp
     platform/android/src/style/conversion/property_value.hpp
     platform/android/src/style/conversion/types.hpp
     platform/android/src/style/conversion/types_string_values.hpp
@@ -213,6 +212,8 @@ add_library(mbgl-android STATIC
     platform/android/src/map_renderer_runnable.hpp
 
     # Java core classes
+    platform/android/src/java/lang.cpp
+    platform/android/src/java/lang.hpp
     platform/android/src/java/util.cpp
     platform/android/src/java/util.hpp
 
diff --git a/platform/android/src/gson/json_array.cpp b/platform/android/src/gson/json_array.cpp
index d91e323ac9..e8852d77e9 100644
--- a/platform/android/src/gson/json_array.cpp
+++ b/platform/android/src/gson/json_array.cpp
@@ -6,7 +6,22 @@ namespace mbgl {
 namespace android {
 namespace gson {
 
-std::vector<mapbox::geometry::value> JsonArray::convert(jni::JNIEnv &env, jni::Object<JsonArray> jsonArray) {
+jni::Object<JsonArray> JsonArray::New(jni::JNIEnv& env, const std::vector<mapbox::geometry::value>& values){
+    static auto constructor = JsonArray::javaClass.GetConstructor(env);
+    static auto addMethod = JsonArray::javaClass.GetMethod<void (jni::Object<JsonElement>)>(env, "add");
+
+    auto jsonArray = JsonArray::javaClass.New(env, constructor);
+
+    for (const auto &v : values) {
+        auto jsonElement = JsonElement::New(env, v);
+        jsonArray.Call(env, addMethod, jsonElement);
+        jni::DeleteLocalRef(env, jsonElement);
+    }
+
+    return jsonArray;
+}
+
+std::vector<mapbox::geometry::value> JsonArray::convert(jni::JNIEnv& env, const jni::Object<JsonArray> jsonArray) {
     std::vector<mapbox::geometry::value> values;
 
     if (jsonArray) {
@@ -28,7 +43,7 @@ std::vector<mapbox::geometry::value> JsonArray::convert(jni::JNIEnv &env, jni::O
     return values;
 }
 
-void JsonArray::registerNative(jni::JNIEnv &env) {
+void JsonArray::registerNative(jni::JNIEnv& env) {
     // Lookup the class
     javaClass = *jni::Class<JsonArray>::Find(env).NewGlobalRef(env).release();
 }
diff --git a/platform/android/src/gson/json_array.hpp b/platform/android/src/gson/json_array.hpp
index 8571ad5dba..c9ae98692f 100644
--- a/platform/android/src/gson/json_array.hpp
+++ b/platform/android/src/gson/json_array.hpp
@@ -13,6 +13,8 @@ class JsonArray : private mbgl::util::noncopyable {
 public:
     static constexpr auto Name() { return "com/google/gson/JsonArray"; };
 
+    static jni::Object<JsonArray> New(jni::JNIEnv&, const std::vector<mapbox::geometry::value>&);
+
     static std::vector<mapbox::geometry::value> convert(JNIEnv&, jni::Object<JsonArray>);
 
     static jni::Class<JsonArray> javaClass;
diff --git a/platform/android/src/gson/json_element.cpp b/platform/android/src/gson/json_element.cpp
index 060b1e0fe2..5eaaf531f4 100644
--- a/platform/android/src/gson/json_element.cpp
+++ b/platform/android/src/gson/json_element.cpp
@@ -11,6 +11,34 @@ namespace mbgl {
 namespace android {
 namespace gson {
 
+/**
+ * Turn mapbox::geometry::value into Java Gson JsonElement
+ */
+class JsonElementEvaluator {
+public:
+
+    jni::JNIEnv& env;
+
+    jni::Object<JsonElement> operator()(const JsonPrimitive::value value) const {
+        return jni::Cast(env, JsonPrimitive::New(env, value), JsonElement::javaClass);
+    }
+
+    jni::Object<JsonElement> operator()(const std::vector<mapbox::geometry::value> &values) const {
+        return jni::Cast(env, JsonArray::New(env, values), JsonElement::javaClass);
+    }
+
+    jni::Object<JsonElement> operator()(const std::unordered_map<std::string, mapbox::geometry::value> &values) const {
+        return jni::Cast(env, JsonObject::New(env, values), JsonElement::javaClass);
+    }
+
+};
+
+
+jni::Object<JsonElement> JsonElement::New(jni::JNIEnv& env, const mapbox::geometry::value& value) {
+  JsonElementEvaluator evaluator { env } ;
+  return mapbox::geometry::value::visit(value, evaluator);
+}
+
 mapbox::geometry::value JsonElement::convert(jni::JNIEnv &env, jni::Object<JsonElement> jsonElement) {
     mapbox::geometry::value value;
 
diff --git a/platform/android/src/gson/json_element.hpp b/platform/android/src/gson/json_element.hpp
index 7619350617..d850caa526 100644
--- a/platform/android/src/gson/json_element.hpp
+++ b/platform/android/src/gson/json_element.hpp
@@ -13,6 +13,8 @@ class JsonElement : private mbgl::util::noncopyable {
 public:
     static constexpr auto Name() { return "com/google/gson/JsonElement"; };
 
+    static jni::Object<JsonElement> New(jni::JNIEnv&, const mapbox::geometry::value&);
+
     static mapbox::geometry::value convert(JNIEnv&, jni::Object<JsonElement>);
 
     static bool isJsonObject(JNIEnv&, jni::Object<JsonElement>);
diff --git a/platform/android/src/gson/json_object.cpp b/platform/android/src/gson/json_object.cpp
index a704dae9dd..61b55f8b9e 100644
--- a/platform/android/src/gson/json_object.cpp
+++ b/platform/android/src/gson/json_object.cpp
@@ -9,6 +9,23 @@ namespace android {
 namespace gson {
 
 
+jni::Object<JsonObject> JsonObject::New(jni::JNIEnv& env, const std::unordered_map<std::string, mapbox::geometry::value>& values) {
+    static auto constructor = JsonObject::javaClass.GetConstructor(env);
+    static auto addMethod = JsonObject::javaClass.GetMethod<void (jni::String, jni::Object<JsonElement>)>(env, "add");
+
+    jni::Object<JsonObject> jsonObject = JsonObject::javaClass.New(env, constructor);
+
+    for (auto &item : values) {
+        jni::Object<JsonElement> jsonElement = JsonElement::New(env, item.second);
+        jni::String key = jni::Make<jni::String>(env, item.first);
+        jsonObject.Call(env, addMethod, key, jsonElement);
+        jni::DeleteLocalRef(env, jsonElement);
+        jni::DeleteLocalRef(env, key);
+    }
+
+    return jsonObject;
+}
+
 template <typename F> // void (jni::String, jni::Object<gson::JsonElement>)
 static void iterateEntrySet(jni::JNIEnv& env, jni::Object<JsonObject> jsonObject, F callback) {
     // Get Set<Map.Entry<String, JsonElement>>
diff --git a/platform/android/src/gson/json_object.hpp b/platform/android/src/gson/json_object.hpp
index aba8e40415..4bc61e51a2 100644
--- a/platform/android/src/gson/json_object.hpp
+++ b/platform/android/src/gson/json_object.hpp
@@ -13,6 +13,8 @@ class JsonObject : private mbgl::util::noncopyable {
 public:
     static constexpr auto Name() { return "com/google/gson/JsonObject"; };
 
+    static jni::Object<JsonObject> New(jni::JNIEnv&, const std::unordered_map<std::string, mapbox::geometry::value>&);
+
     static mapbox::geometry::property_map convert(JNIEnv&, jni::Object<JsonObject>);
 
     static jni::Class<JsonObject> javaClass;
diff --git a/platform/android/src/gson/json_primitive.cpp b/platform/android/src/gson/json_primitive.cpp
index 58d0b45fe7..4e171c4845 100644
--- a/platform/android/src/gson/json_primitive.cpp
+++ b/platform/android/src/gson/json_primitive.cpp
@@ -1,9 +1,89 @@
 #include "json_primitive.hpp"
+#include "../java/lang.hpp"
 
 namespace mbgl {
 namespace android {
 namespace gson {
 
+/**
+ * Turn mapbox::geometry::value into Java Gson JsonPrimitives
+ */
+class JsonPrimitiveEvaluator {
+public:
+
+    jni::JNIEnv& env;
+
+    /**
+     * Create a null primitive
+     */
+    jni::Object<JsonPrimitive> operator()(const mapbox::geometry::null_value_t) const {
+        return jni::Object<JsonPrimitive>();
+    }
+
+    /**
+     * Create a primitive containing a string value
+     */
+    jni::Object<JsonPrimitive> operator()(const std::string value) const {
+        static auto constructor = JsonPrimitive::javaClass.GetConstructor<jni::String>(env);
+        auto jvalue = jni::Make<jni::String>(env, value);
+        auto jsonPrimitive = JsonPrimitive::javaClass.New(env, constructor, jvalue);
+        jni::DeleteLocalRef(env, jvalue);
+        return jsonPrimitive;
+    }
+
+    /**
+     * Create a primitive containing a number value with type double
+     */
+    jni::Object<JsonPrimitive> operator()(const double value) const {
+        static auto constructor = JsonPrimitive::javaClass.GetConstructor<jni::Object<java::lang::Number>>(env);
+        auto boxedValue = java::lang::Double::valueOf(env, value);
+        auto number = jni::Cast(env, boxedValue, java::lang::Number::javaClass);
+        auto jsonPrimitive = JsonPrimitive::javaClass.New(env, constructor, number);
+        jni::DeleteLocalRef(env, boxedValue);
+        return jsonPrimitive;
+    }
+
+    /**
+     * Create a primitive containing a number value with type long
+     */
+    jni::Object<JsonPrimitive> operator()(const int64_t value) const {
+        static auto constructor = JsonPrimitive::javaClass.GetConstructor<jni::Object<java::lang::Number>>(env);
+        auto boxedValue = java::lang::Long::valueOf(env, value);
+        auto number = jni::Cast(env, boxedValue, java::lang::Number::javaClass);
+        auto jsonPrimitive =  JsonPrimitive::javaClass.New(env, constructor, number);
+        jni::DeleteLocalRef(env, boxedValue);
+        return jsonPrimitive;
+    }
+
+    /**
+     * Create a primitive containing a number value with type long
+     */
+    jni::Object<JsonPrimitive> operator()(const uint64_t value) const {
+        static auto constructor = JsonPrimitive::javaClass.GetConstructor<jni::Object<java::lang::Number>>(env);
+        auto boxedValue = java::lang::Long::valueOf(env, value);
+        auto number = jni::Cast(env, boxedValue, java::lang::Number::javaClass);
+        auto jsonPrimitive = JsonPrimitive::javaClass.New(env, constructor, number);
+        jni::DeleteLocalRef(env, boxedValue);
+        return jsonPrimitive;
+    }
+
+    /**
+     * Create a primitive containing a boolean value
+     */
+    jni::Object<JsonPrimitive> operator()(const bool value) const {
+        static auto constructor = JsonPrimitive::javaClass.GetConstructor<jni::Object<java::lang::Boolean>>(env);
+        auto boxedValue = java::lang::Boolean::valueOf(env, value);
+        auto jsonPrimitive = JsonPrimitive::javaClass.New(env, constructor, boxedValue);
+        jni::DeleteLocalRef(env, boxedValue);
+        return jsonPrimitive;
+    }
+};
+
+jni::Object<JsonPrimitive> JsonPrimitive::New(jni::JNIEnv &env, const value& value) {
+    JsonPrimitiveEvaluator evaluator { env };
+    return value::visit(value, evaluator);
+}
+
 JsonPrimitive::value JsonPrimitive::convert(jni::JNIEnv &env, jni::Object<JsonPrimitive> jsonPrimitive) {
     value value;
     if (jsonPrimitive) {
diff --git a/platform/android/src/gson/json_primitive.hpp b/platform/android/src/gson/json_primitive.hpp
index 5fc8a2b485..c418e0ebe8 100644
--- a/platform/android/src/gson/json_primitive.hpp
+++ b/platform/android/src/gson/json_primitive.hpp
@@ -15,6 +15,8 @@ public:
 
     static constexpr auto Name() { return "com/google/gson/JsonPrimitive"; };
 
+    static jni::Object<JsonPrimitive> New(jni::JNIEnv&, const value&);
+
     static value convert(JNIEnv&, jni::Object<JsonPrimitive>);
 
     static bool isBoolean(JNIEnv&, jni::Object<JsonPrimitive>);
diff --git a/platform/android/src/java/lang.cpp b/platform/android/src/java/lang.cpp
new file mode 100644
index 0000000000..3c95737169
--- /dev/null
+++ b/platform/android/src/java/lang.cpp
@@ -0,0 +1,76 @@
+#include "lang.hpp"
+
+namespace mbgl {
+namespace android {
+namespace java {
+namespace lang {
+
+// Float
+
+jni::Object<Float> Float::valueOf(JNIEnv &env, jfloat value) {
+    static auto method = javaClass.GetStaticMethod<jni::Object<Float> (jni::jfloat)>(env, "valueOf");
+    return javaClass.Call(env, method, value);
+}
+
+void Float::registerNative(jni::JNIEnv &env) {
+    // Lookup the class
+    javaClass = *jni::Class<Float>::Find(env).NewGlobalRef(env).release();
+}
+
+jni::Class<Float> Float::javaClass;
+
+// Long
+
+jni::Object<Long> Long::valueOf(JNIEnv &env, jlong value) {
+    static auto method = javaClass.GetStaticMethod<jni::Object<Long> (jni::jlong)>(env, "valueOf");
+    return javaClass.Call(env, method, value);
+}
+
+void Long::registerNative(jni::JNIEnv &env) {
+    // Lookup the class
+    javaClass = *jni::Class<Long>::Find(env).NewGlobalRef(env).release();
+}
+
+jni::Class<Long> Long::javaClass;
+
+// Double
+
+jni::Object<Double> Double::valueOf(JNIEnv &env, jdouble value) {
+    static auto method = javaClass.GetStaticMethod<jni::Object<Double> (jni::jdouble)>(env, "valueOf");
+    return javaClass.Call(env, method, value);
+}
+
+void Double::registerNative(jni::JNIEnv &env) {
+    // Lookup the class
+    javaClass = *jni::Class<Double>::Find(env).NewGlobalRef(env).release();
+}
+
+jni::Class<Double> Double::javaClass;
+
+// Boolean
+
+jni::Object<Boolean> Boolean::valueOf(JNIEnv &env, jboolean value) {
+    static auto method = javaClass.GetStaticMethod<jni::Object<Boolean> (jni::jboolean)>(env, "valueOf");
+    return javaClass.Call(env, method, value);
+}
+
+void Boolean::registerNative(jni::JNIEnv &env) {
+    // Lookup the class
+    javaClass = *jni::Class<Boolean>::Find(env).NewGlobalRef(env).release();
+}
+
+jni::Class<Boolean> Boolean::javaClass;
+
+// Number
+
+void Number::registerNative(jni::JNIEnv &env) {
+    // Lookup the class
+    javaClass = *jni::Class<Number>::Find(env).NewGlobalRef(env).release();
+}
+
+jni::Class<Number> Number::javaClass;
+
+} // namespace lang
+} // namespace java
+} // namespace android
+} // namespace mbgl
diff --git a/platform/android/src/java/lang.hpp b/platform/android/src/java/lang.hpp
index dcf81a9d0c..981e3b14b7 100644
--- a/platform/android/src/java/lang.hpp
+++ b/platform/android/src/java/lang.hpp
@@ -1,18 +1,64 @@
 #pragma once
 
+#include <jni/jni.hpp>
+#include <mbgl/util/noncopyable.hpp>
+
 namespace mbgl {
 namespace android {
 namespace java {
 namespace lang {
 
-class Float {
+class Float : private mbgl::util::noncopyable {
 public:
     static constexpr auto Name() { return "java/lang/Float"; };
+
+    static jni::Object<Float> valueOf(JNIEnv&, jfloat);
+
+    static jni::Class<Float> javaClass;
+
+    static void registerNative(jni::JNIEnv&);
+};
+
+class Double : private mbgl::util::noncopyable {
+public:
+    static constexpr auto Name() { return "java/lang/Double"; };
+
+    static jni::Object<Double> valueOf(JNIEnv&, jdouble);
+
+    static jni::Class<Double> javaClass;
+
+    static void registerNative(jni::JNIEnv&);
+};
+
+class Long : private mbgl::util::noncopyable {
+public:
+    static constexpr auto Name() { return "java/lang/Long"; };
+
+    static jni::Object<Long> valueOf(JNIEnv&, jlong);
+
+    static jni::Class<Long> javaClass;
+
+    static void registerNative(jni::JNIEnv&);
+};
+
+class Boolean : private mbgl::util::noncopyable {
+public:
+    static constexpr auto Name() { return "java/lang/Boolean"; };
+
+    static jni::Object<Boolean> valueOf(JNIEnv&, jboolean);
+
+    static jni::Class<Boolean> javaClass;
+
+    static void registerNative(jni::JNIEnv&);
 };
 
-class Number {
+class Number : private mbgl::util::noncopyable {
 public:
     static constexpr auto Name() { return "java/lang/Number"; };
+
+    static jni::Class<Number> javaClass;
+
+    static void registerNative(jni::JNIEnv&);
 };
 
 } // namespace lang
diff --git a/platform/android/src/jni.cpp b/platform/android/src/jni.cpp
index c8c20e939a..2f6ed96ab0 100755
--- a/platform/android/src/jni.cpp
+++ b/platform/android/src/jni.cpp
@@ -47,6 +47,7 @@
 #include "snapshotter/map_snapshotter.hpp"
 #include "snapshotter/map_snapshot.hpp"
 #include "text/local_glyph_rasterizer_jni.hpp"
+#include "java/lang.hpp"
 
 namespace mbgl {
 namespace android {
@@ -112,6 +113,11 @@ void registerNatives(JavaVM *vm) {
     java::util::registerNative(env);
     PointF::registerNative(env);
     RectF::registerNative(env);
+    java::lang::Number::registerNative(env);
+    java::lang::Float::registerNative(env);
+    java::lang::Boolean::registerNative(env);
+    java::lang::Double::registerNative(env);
+    java::lang::Long::registerNative(env);
 
     // GeoJSON
     geojson::Feature::registerNative(env);
diff --git a/platform/android/src/style/conversion/function.hpp b/platform/android/src/style/conversion/function.hpp
index 510efd3c94..d6669b4508 100644
--- a/platform/android/src/style/conversion/function.hpp
+++ b/platform/android/src/style/conversion/function.hpp
@@ -7,7 +7,8 @@
 #include "../../java/lang.hpp"
 
 #include <jni/jni.hpp>
-#include "gson.hpp"
+#include "../../gson/json_element.hpp"
+
 #include <tuple>
 #include <map>
 
@@ -16,41 +17,32 @@ namespace android {
 namespace conversion {
 
 template <class T>
-struct Converter<jni::jobject*, mbgl::style::CameraFunction<T>> {
+struct Converter<jni::Object<android::gson::JsonElement>, mbgl::style::CameraFunction<T>> {
 
-    Result<jni::jobject*> operator()(jni::JNIEnv& env, const mbgl::style::CameraFunction<T>& value) const {
+    Result<jni::Object<android::gson::JsonElement>> operator()(jni::JNIEnv& env, const mbgl::style::CameraFunction<T>& value) const {
         // Convert expressions
         mbgl::Value expressionValue = value.getExpression().serialize();
-        JsonEvaluator jsonEvaluator{env};
-        jni::jobject* converted = apply_visitor(jsonEvaluator, expressionValue);
-
-        return converted;
+        return gson::JsonElement::New(env, expressionValue);
     }
 };
 
 template <class T>
-struct Converter<jni::jobject*, mbgl::style::SourceFunction<T>> {
+struct Converter<jni::Object<android::gson::JsonElement>, mbgl::style::SourceFunction<T>> {
 
-    Result<jni::jobject*> operator()(jni::JNIEnv& env, const mbgl::style::SourceFunction<T>& value) const {
+    Result<jni::Object<android::gson::JsonElement>> operator()(jni::JNIEnv& env, const mbgl::style::SourceFunction<T>& value) const {
         // Convert expressions
         mbgl::Value expressionValue = value.getExpression().serialize();
-        JsonEvaluator jsonEvaluator{env};
-        jni::jobject* converted = apply_visitor(jsonEvaluator, expressionValue);
-
-        return converted;
+        return gson::JsonElement::New(env, expressionValue);
     }
 };
 
 template <class T>
-struct Converter<jni::jobject*, mbgl::style::CompositeFunction<T>> {
+struct Converter<jni::Object<android::gson::JsonElement>, mbgl::style::CompositeFunction<T>> {
 
-    Result<jni::jobject*> operator()(jni::JNIEnv& env, const mbgl::style::CompositeFunction<T>& value) const {
+    Result<jni::Object<android::gson::JsonElement>> operator()(jni::JNIEnv& env, const mbgl::style::CompositeFunction<T>& value) const {
         // Convert expressions
         mbgl::Value expressionValue = value.getExpression().serialize();
-        JsonEvaluator jsonEvaluator{env};
-        jni::jobject* converted = apply_visitor(jsonEvaluator, expressionValue);
-
-        return converted;
+        return gson::JsonElement::New(env, expressionValue);
     }
 };
 
diff --git a/platform/android/src/style/conversion/gson.hpp b/platform/android/src/style/conversion/gson.hpp
deleted file mode 100644
index 02c3fdd30d..0000000000
--- a/platform/android/src/style/conversion/gson.hpp
+++ /dev/null
@@ -1,114 +0,0 @@
-#pragma once
-
-#include "../../conversion/constant.hpp"
-#include "../../conversion/collection.hpp"
-
-#include <mapbox/geometry.hpp>
-#include <jni/jni.hpp>
-#include "../../jni/local_object.hpp"
-#include "mapbox/geometry/feature.hpp"
-
-namespace mbgl {
-namespace android {
-namespace conversion {
-
-/**
- * Turn mapbox::geometry::value type into Java Json
- */
-class JsonEvaluator {
-public:
-
-    jni::JNIEnv& env;
-
-    jni::jobject* operator()(const mapbox::geometry::null_value_t) const {
-       return (jni::jobject*) nullptr;;
-    }
-
-    jni::jobject* operator()(const bool& value) const {
-        static jni::jclass* javaClass = jni::NewGlobalRef(env, &jni::FindClass(env, "com/google/gson/JsonPrimitive")).release();
-        static jni::jmethodID* constructor = &jni::GetMethodID(env, *javaClass, "<init>", "(Ljava/lang/Boolean;)V");
-
-        // Create JsonPrimitive
-        jni::LocalObject<jni::jobject> converted = jni::NewLocalObject(env, *convert<jni::jobject*, bool>(env, value));
-        jni::jobject* object = &jni::NewObject(env, *javaClass, *constructor, *converted);
-
-        return object;
-    }
-
-    template <class Number>
-    jni::jobject* operator()(const Number& value) const {
-        static jni::jclass* javaClass = jni::NewGlobalRef(env, &jni::FindClass(env, "com/google/gson/JsonPrimitive")).release();
-        static jni::jmethodID* constructor = &jni::GetMethodID(env, *javaClass, "<init>", "(Ljava/lang/Number;)V");
-
-        // Create JsonPrimitive
-        jni::LocalObject<jni::jobject> converted = jni::NewLocalObject(env, *convert<jni::jobject*, Number>(env, value));
-        jni::jobject* object = &jni::NewObject(env, *javaClass, *constructor, converted.get());
-
-        return object;
-    }
-
-    jni::jobject* operator()(const std::string value) const {
-        static jni::jclass* javaClass = jni::NewGlobalRef(env, &jni::FindClass(env, "com/google/gson/JsonPrimitive")).release();
-        static jni::jmethodID* constructor = &jni::GetMethodID(env, *javaClass, "<init>", "(Ljava/lang/String;)V");
-
-        // Create JsonPrimitive
-        jni::LocalObject<jni::jobject> converted = jni::NewLocalObject(env, *convert<jni::jobject*, std::string>(env, value));
-        jni::jobject* object = &jni::NewObject(env, *javaClass, *constructor, converted.get());
-
-        return object;
-    }
-
-    jni::jobject* operator()(const std::vector<mapbox::geometry::value> values) const {
-        static jni::jclass* javaClass = jni::NewGlobalRef(env, &jni::FindClass(env, "com/google/gson/JsonArray")).release();
-        static jni::jmethodID* constructor = &jni::GetMethodID(env, *javaClass, "<init>", "()V");;
-        static jni::jmethodID* add = &jni::GetMethodID(env, *javaClass, "add", "(Lcom/google/gson/JsonElement;)V");
-
-        // Create json array
-        jni::jobject* jarray = &jni::NewObject(env, *javaClass, *constructor);
-
-        // Add values
-        for (const auto &v : values) {
-            jni::LocalObject<jni::jobject> converted = jni::NewLocalObject(env, mapbox::geometry::value::visit(v, *this));
-            jni::CallMethod<void>(env, jarray, *add, converted.get());
-        }
-
-        return jarray;
-    }
-
-    jni::jobject* operator()(const std::unordered_map<std::string, mapbox::geometry::value> value) const {
-        static jni::jclass* javaClass = jni::NewGlobalRef(env, &jni::FindClass(env, "com/google/gson/JsonObject")).release();
-        static jni::jmethodID* constructor = &jni::GetMethodID(env, *javaClass, "<init>", "()V");;
-        static jni::jmethodID* add = &jni::GetMethodID(env, *javaClass, "add", "(Ljava/lang/String;Lcom/google/gson/JsonElement;)V");
-
-        // Create json object
-        jni::jobject* jsonObject = &jni::NewObject(env, *javaClass, *constructor);
-
-        // Add items
-        for (auto &item : value) {
-            jni::LocalObject<jni::jobject> converted = jni::NewLocalObject(env, mbgl::Value::visit(item.second, *this));
-            jni::LocalObject<jni::jobject> key = jni::NewLocalObject(env, *convert<jni::jobject*, std::string>(env, item.first));
-            jni::CallMethod<void>(env, jsonObject, *add, key.get(), converted.get());
-        }
-
-        return jsonObject;
-    }
-
-private:
-
-};
-
-/**
- * mapbox::geometry::value -> Java Json
- */
-template <>
-struct Converter<jni::jobject*, mapbox::geometry::value> {
-    Result<jni::jobject*> operator()(jni::JNIEnv& env, const mapbox::geometry::value& value) const {
-        JsonEvaluator evaluator { env } ;
-        jni::jobject* converted = mapbox::geometry::value::visit(value, evaluator);
-        return { converted };
-    }
-};
-
-}
-}
-}
diff --git a/platform/android/src/style/conversion/property_value.hpp b/platform/android/src/style/conversion/property_value.hpp
index 4ed25eac25..902d1e80b2 100644
--- a/platform/android/src/style/conversion/property_value.hpp
+++ b/platform/android/src/style/conversion/property_value.hpp
@@ -7,7 +7,6 @@
 #include "../../conversion/constant.hpp"
 #include "types.hpp"
 #include "function.hpp"
-#include "gson.hpp"
 
 namespace mbgl {
 namespace android {
@@ -32,15 +31,15 @@ public:
     }
 
     jni::jobject* operator()(const mbgl::style::CameraFunction<T> &value) const {
-        return *convert<jni::jobject*, mbgl::style::CameraFunction<T>>(env, value);
+        return *convert<jni::Object<android::gson::JsonElement>, mbgl::style::CameraFunction<T>>(env, value);
     }
 
     jni::jobject* operator()(const mbgl::style::SourceFunction<T> &value) const {
-        return *convert<jni::jobject*, mbgl::style::SourceFunction<T>>(env, value);
+        return *convert<jni::Object<android::gson::JsonElement>, mbgl::style::SourceFunction<T>>(env, value);
     }
 
     jni::jobject* operator()(const mbgl::style::CompositeFunction<T> &value) const {
-        return *convert<jni::jobject*, mbgl::style::CompositeFunction<T>>(env, value);
+        return *convert<jni::Object<android::gson::JsonElement>, mbgl::style::CompositeFunction<T>>(env, value);
     }
 
 private:
diff --git a/platform/android/src/style/layers/layer.cpp b/platform/android/src/style/layers/layer.cpp
index a2f4087fce..6fe6e3cb29 100644
--- a/platform/android/src/style/layers/layer.cpp
+++ b/platform/android/src/style/layers/layer.cpp
@@ -26,7 +26,6 @@
 // C++ -> Java conversion
 #include "../conversion/property_value.hpp"
 #include <mbgl/style/filter.hpp>
-#include "../conversion/gson.hpp"
 
 #include <string>
 
@@ -153,20 +152,19 @@ namespace android {
         }
     };
 
-    jni::Object<gson::JsonArray> Layer::getFilter(jni::JNIEnv& env) {
+    jni::Object<gson::JsonElement> Layer::getFilter(jni::JNIEnv& env) {
         using namespace mbgl::style;
         using namespace mbgl::style::conversion;
 
         Filter filter = layer.accept(GetFilterEvaluator());
 
-        jni::jobject* converted = nullptr;
+        jni::Object<gson::JsonElement> converted;
         if (filter.is<ExpressionFilter>()) {
             ExpressionFilter filterExpression = filter.get<ExpressionFilter>();
             mbgl::Value expressionValue = filterExpression.expression.get()->serialize();
-            conversion::JsonEvaluator jsonEvaluator{env};
-            converted = apply_visitor(jsonEvaluator, expressionValue);
+            converted = gson::JsonElement::New(env, expressionValue);
         }
-        return jni::Object<gson::JsonArray>(converted);
+        return converted;
     }
 
     struct SetSourceLayerEvaluator {
diff --git a/platform/android/src/style/layers/layer.hpp b/platform/android/src/style/layers/layer.hpp
index 19713a1baa..2486b0dfa6 100644
--- a/platform/android/src/style/layers/layer.hpp
+++ b/platform/android/src/style/layers/layer.hpp
@@ -5,6 +5,7 @@
 #include <mbgl/style/layer.hpp>
 #include "../../gson/json_array.hpp"
 #include "../value.hpp"
+#include "../../gson/json_element.hpp"
 
 #include <jni/jni.hpp>
 
@@ -68,7 +69,7 @@ public:
 
     void setFilter(jni::JNIEnv&, jni::Array<jni::Object<>>);
 
-    jni::Object<gson::JsonArray> getFilter(jni::JNIEnv&);
+    jni::Object<gson::JsonElement> getFilter(jni::JNIEnv&);
 
     void setSourceLayer(jni::JNIEnv&, jni::String);