[android] Move conversion code to .cpp files

19 files changed, 493 insertions, 387 deletions

diff --git a/platform/android/core-files.txt b/platform/android/core-files.txt
index 7d86cb5615..ef9ec65df7 100644
--- a/platform/android/core-files.txt
+++ b/platform/android/core-files.txt
@@ -48,12 +48,27 @@ platform/default/mbgl/map/map_snapshotter.hpp
 platform/linux/src/headless_backend_egl.cpp
 
 # Conversion C++ -> Java
+platform/android/src/conversion/collection.cpp
+platform/android/src/conversion/collection.hpp
+platform/android/src/conversion/color.cpp
+platform/android/src/conversion/color.hpp
+platform/android/src/conversion/constant.cpp
 platform/android/src/conversion/constant.hpp
 platform/android/src/conversion/conversion.hpp
+platform/android/src/geojson/conversion/feature.cpp
+platform/android/src/geojson/conversion/feature.hpp
+platform/android/src/style/conversion/filter.cpp
+platform/android/src/style/conversion/filter.hpp
+platform/android/src/style/conversion/position.cpp
+platform/android/src/style/conversion/position.hpp
 platform/android/src/style/conversion/property_expression.hpp
 platform/android/src/style/conversion/property_value.hpp
+platform/android/src/style/conversion/transition_options.cpp
+platform/android/src/style/conversion/transition_options.hpp
 platform/android/src/style/conversion/types.hpp
 platform/android/src/style/conversion/types_string_values.hpp
+platform/android/src/style/conversion/url_or_tileset.cpp
+platform/android/src/style/conversion/url_or_tileset.hpp
 platform/android/src/map/camera_position.cpp
 platform/android/src/map/camera_position.hpp
 platform/android/src/map/image.cpp
diff --git a/platform/android/src/conversion/collection.cpp b/platform/android/src/conversion/collection.cpp
new file mode 100644
index 0000000000..14d817ea88
--- /dev/null
+++ b/platform/android/src/conversion/collection.cpp
@@ -0,0 +1,38 @@
+#include "collection.hpp"
+#include "constant.hpp"
+
+namespace mbgl {
+namespace android {
+namespace conversion {
+
+std::vector<std::string> toVector(JNIEnv& env, jni::jarray<jni::jobject>& array) {
+    std::vector<std::string> vector;
+    std::size_t len = jni::GetArrayLength(env, array);
+    vector.reserve(len);
+
+    for (std::size_t i = 0; i < len; i++) {
+        jni::jstring* jstr = reinterpret_cast<jni::jstring*>(jni::GetObjectArrayElement(env, array, i));
+        vector.push_back(*convert<std::string, jni::String>(env, jni::String(jstr)));
+        jni::DeleteLocalRef(env, jstr);
+    }
+
+    return vector;
+}
+
+std::vector<std::string> toVector(JNIEnv& env, jni::Array<jni::String> array) {
+    std::size_t len = array.Length(env);
+    std::vector<std::string> vector;
+    vector.reserve(len);
+
+    for (std::size_t i = 0; i < len; i++) {
+        jni::String jstr = array.Get(env, i);
+        vector.push_back(*convert<std::string, jni::String>(env, jstr));
+        jni::DeleteLocalRef(env, jstr);
+    }
+
+    return vector;
+}
+
+}
+}
+}
diff --git a/platform/android/src/conversion/collection.hpp b/platform/android/src/conversion/collection.hpp
index 2b953e73f4..973897b212 100644
--- a/platform/android/src/conversion/collection.hpp
+++ b/platform/android/src/conversion/collection.hpp
@@ -1,9 +1,7 @@
 #pragma once
 
 #include "conversion.hpp"
-#include "constant.hpp"
 
-#include <mbgl/util/optional.hpp>
 #include <jni/jni.hpp>
 
 #include <vector>
@@ -16,7 +14,7 @@ namespace conversion {
  * Convert jarray -> ArrayList
  */
 template <class T>
-inline jni::jobject* toArrayList(JNIEnv& env, jni::jarray<T>& array) {
+jni::jobject* toArrayList(JNIEnv& env, jni::jarray<T>& array) {
     static jni::jclass* javaClass = jni::NewGlobalRef(env, &jni::FindClass(env, "java/util/Arrays")).release();
     static jni::jmethodID* asList = &jni::GetStaticMethodID(env, *javaClass, "asList", "([Ljava/lang/Object;)Ljava/util/List;");
     return reinterpret_cast<jni::jobject*>(jni::CallStaticMethod<jni::jobject*>(env, *javaClass, *asList, array));
@@ -24,34 +22,8 @@ inline jni::jobject* toArrayList(JNIEnv& env, jni::jarray<T>& array) {
 
 // Java -> C++
 
-
-inline std::vector<std::string> toVector(JNIEnv& env, jni::jarray<jni::jobject>& array) {
-    std::vector<std::string> vector;
-    std::size_t len = jni::GetArrayLength(env, array);
-    vector.reserve(len);
-
-    for (std::size_t i = 0; i < len; i++) {
-        jni::jstring* jstr = reinterpret_cast<jni::jstring*>(jni::GetObjectArrayElement(env, array, i));
-        vector.push_back(*convert<std::string, jni::String>(env, jni::String(jstr)));
-        jni::DeleteLocalRef(env, jstr);
-    }
-
-    return vector;
-}
-
-inline std::vector<std::string> toVector(JNIEnv& env, jni::Array<jni::String> array) {
-    std::size_t len = array.Length(env);
-    std::vector<std::string> vector;
-    vector.reserve(len);
-
-    for (std::size_t i = 0; i < len; i++) {
-        jni::String jstr = array.Get(env, i);
-        vector.push_back(*convert<std::string, jni::String>(env, jstr));
-        jni::DeleteLocalRef(env, jstr);
-    }
-
-    return vector;
-}
+std::vector<std::string> toVector(JNIEnv& env, jni::jarray<jni::jobject>& array);
+std::vector<std::string> toVector(JNIEnv& env, jni::Array<jni::String> array);
 
 }
 }
diff --git a/platform/android/src/conversion/color.cpp b/platform/android/src/conversion/color.cpp
new file mode 100644
index 0000000000..ce85943e61
--- /dev/null
+++ b/platform/android/src/conversion/color.cpp
@@ -0,0 +1,17 @@
+#include "color.hpp"
+
+namespace mbgl {
+namespace android {
+namespace conversion {
+
+Result<mbgl::Color> Converter<mbgl::Color, int>::operator()(jni::JNIEnv&, const int& color) const {
+    float r = (color >> 16) & 0xFF;
+    float g = (color >> 8) & 0xFF;
+    float b = (color) & 0xFF;
+    float a = (color >> 24) & 0xFF;
+    return { mbgl::Color( r / 255.0f, g / 255.0f, b / 255.0f, a / 255.0f ) };
+}
+
+} // namespace conversion
+} // namespace style
+} // namespace mbgl
diff --git a/platform/android/src/conversion/color.hpp b/platform/android/src/conversion/color.hpp
index 40aa68d4a9..2b4144b933 100644
--- a/platform/android/src/conversion/color.hpp
+++ b/platform/android/src/conversion/color.hpp
@@ -10,13 +10,7 @@ namespace conversion {
 
 template <>
 struct Converter<mbgl::Color, int> {
-    Result<mbgl::Color> operator()(jni::JNIEnv&, const int& color) const {
-        float r = (color >> 16) & 0xFF;
-        float g = (color >> 8) & 0xFF;
-        float b = (color) & 0xFF;
-        float a = (color >> 24) & 0xFF;
-        return { mbgl::Color( r / 255.0f, g / 255.0f, b / 255.0f, a / 255.0f ) };
-    }
+    Result<mbgl::Color> operator()(jni::JNIEnv&, const int& color) const;
 };
 
 } // namespace conversion
diff --git a/platform/android/src/conversion/constant.cpp b/platform/android/src/conversion/constant.cpp
new file mode 100644
index 0000000000..cce0796ce5
--- /dev/null
+++ b/platform/android/src/conversion/constant.cpp
@@ -0,0 +1,86 @@
+#include "constant.hpp"
+
+#include <sstream>
+
+namespace mbgl {
+namespace android {
+namespace conversion {
+
+Result<jni::jobject*> Converter<jni::jobject*, bool>::operator()(jni::JNIEnv& env, const bool& value) const {
+    static jni::jclass* javaClass = jni::NewGlobalRef(env, &jni::FindClass(env, "java/lang/Boolean")).release();
+    static jni::jmethodID* constructor = &jni::GetMethodID(env, *javaClass, "<init>", "(Z)V");
+    return {&jni::NewObject(env, *javaClass, *constructor, (jboolean) value)};
+}
+
+Result<jni::jboolean> Converter<jni::jboolean, bool>::operator()(jni::JNIEnv&, const bool& value) const {
+    return {(jni::jboolean) value};
+}
+
+Result<jni::jobject*> Converter<jni::jobject*, float>::operator()(jni::JNIEnv& env, const float& value) const {
+    static jni::jclass* javaClass = jni::NewGlobalRef(env, &jni::FindClass(env, "java/lang/Float")).release();
+    static jni::jmethodID* constructor = &jni::GetMethodID(env, *javaClass, "<init>", "(F)V");
+    return {&jni::NewObject(env, *javaClass, *constructor, (jfloat) value)};
+}
+
+Result<jni::jfloat> Converter<jni::jfloat, float>::operator()(jni::JNIEnv&, const float& value) const {
+    return {(jni::jfloat) value};
+}
+
+Result<jni::jobject*> Converter<jni::jobject*, double>::operator()(jni::JNIEnv& env, const double& value) const {
+    static jni::jclass* javaClass = jni::NewGlobalRef(env, &jni::FindClass(env, "java/lang/Double")).release();
+    static jni::jmethodID* constructor = &jni::GetMethodID(env, *javaClass, "<init>", "(D)V");
+    return {&jni::NewObject(env, *javaClass, *constructor, (jfloat) value)};
+}
+
+Result<jni::jdouble> Converter<jni::jdouble, float>::operator()(jni::JNIEnv&, const double& value) const {
+    return {(jni::jdouble) value};
+}
+
+Result<jni::jobject*> Converter<jni::jobject*, std::string>::operator()(jni::JNIEnv& env, const std::string& value) const {
+    return {jni::Make<jni::String>(env, value).Get()};
+}
+
+Result<jni::jstring*> Converter<jni::jstring*, std::string>::operator()(jni::JNIEnv& env, const std::string& value) const {
+    return {jni::Make<jni::String>(env, value).Get()};
+}
+
+Result<jni::jobject*> Converter<jni::jobject*, Color>::operator()(jni::JNIEnv& env, const Color& value) const {
+    std::stringstream sstream;
+    sstream << "rgba(" << value.r << ", " << value.g << ", " << value.b << ", "  << value.a << ")";
+    std::string result = sstream.str();
+    return convert<jni::jobject*, std::string>(env, result);
+}
+
+Result<jni::jobject*> Converter<jni::jobject*, std::vector<std::string>>::operator()(jni::JNIEnv& env, const std::vector<std::string>& value) const {
+    static jni::jclass* stringCass = jni::NewGlobalRef(env, &jni::FindClass(env, "java/lang/String")).release();
+    jni::jarray<jni::jobject>& jarray = jni::NewObjectArray(env, value.size(), *stringCass);
+
+    for(size_t i = 0; i < value.size(); i = i + 1) {
+        Result<jni::jobject*> converted = convert<jni::jobject*, std::string>(env, value.at(i));
+        jni::SetObjectArrayElement(env, jarray, i, *converted);
+    }
+
+    return &jarray;
+}
+
+Result<jni::jobject*> Converter<jni::jobject*, std::vector<float>>::operator()(jni::JNIEnv& env, const std::vector<float>& value) const {
+    static jni::jclass* floatClass = jni::NewGlobalRef(env, &jni::FindClass(env, "java/lang/Float")).release();
+    jni::jarray<jni::jobject>& jarray = jni::NewObjectArray(env, value.size(), *floatClass);
+
+    for(size_t i = 0; i < value.size(); i = i + 1) {
+        Result<jni::jobject*> converted = convert<jni::jobject*, float>(env, value.at(i));
+        jni::SetObjectArrayElement(env, jarray, i, *converted);
+    }
+
+    return &jarray;
+}
+
+// Java -> C++
+
+Result<std::string> Converter<std::string, jni::String>::operator()(jni::JNIEnv& env, const jni::String& value) const {
+    return { jni::Make<std::string>(env, value) };
+}
+
+} // namespace conversion
+} // namespace style
+} // namespace mbgl
diff --git a/platform/android/src/conversion/constant.hpp b/platform/android/src/conversion/constant.hpp
index f1c72eb5dd..52395cb9ee 100644
--- a/platform/android/src/conversion/constant.hpp
+++ b/platform/android/src/conversion/constant.hpp
@@ -2,14 +2,12 @@
 
 #include "conversion.hpp"
 
-#include <mbgl/util/optional.hpp>
 #include <mbgl/util/color.hpp>
 #include <jni/jni.hpp>
 
 #include <string>
 #include <array>
 #include <vector>
-#include <sstream>
 
 namespace mbgl {
 namespace android {
@@ -17,51 +15,33 @@ namespace conversion {
 
 template <>
 struct Converter<jni::jobject*, bool> {
-    Result<jni::jobject*> operator()(jni::JNIEnv& env, const bool& value) const {
-        static jni::jclass* javaClass = jni::NewGlobalRef(env, &jni::FindClass(env, "java/lang/Boolean")).release();
-        static jni::jmethodID* constructor = &jni::GetMethodID(env, *javaClass, "<init>", "(Z)V");
-        return {&jni::NewObject(env, *javaClass, *constructor, (jboolean) value)};
-    }
+    Result<jni::jobject*> operator()(jni::JNIEnv& env, const bool& value) const;
 };
 
 template <>
 struct Converter<jni::jboolean, bool> {
-    Result<jni::jboolean> operator()(jni::JNIEnv&, const bool& value) const {
-        return {(jni::jboolean) value};
-    }
+    Result<jni::jboolean> operator()(jni::JNIEnv&, const bool& value) const;
 };
 
 template <>
 struct Converter<jni::jobject*, float> {
-    Result<jni::jobject*> operator()(jni::JNIEnv& env, const float& value) const {
-        static jni::jclass* javaClass = jni::NewGlobalRef(env, &jni::FindClass(env, "java/lang/Float")).release();
-        static jni::jmethodID* constructor = &jni::GetMethodID(env, *javaClass, "<init>", "(F)V");
-        return {&jni::NewObject(env, *javaClass, *constructor, (jfloat) value)};
-    }
+    Result<jni::jobject*> operator()(jni::JNIEnv& env, const float& value) const;
 };
 
 template <>
 struct Converter<jni::jfloat, float> {
-    Result<jni::jfloat> operator()(jni::JNIEnv&, const float& value) const {
-        return {(jni::jfloat) value};
-    }
+    Result<jni::jfloat> operator()(jni::JNIEnv&, const float& value) const;
 };
 
 
 template <>
 struct Converter<jni::jobject*, double> {
-    Result<jni::jobject*> operator()(jni::JNIEnv& env, const double& value) const {
-        static jni::jclass* javaClass = jni::NewGlobalRef(env, &jni::FindClass(env, "java/lang/Double")).release();
-        static jni::jmethodID* constructor = &jni::GetMethodID(env, *javaClass, "<init>", "(D)V");
-        return {&jni::NewObject(env, *javaClass, *constructor, (jfloat) value)};
-    }
+    Result<jni::jobject*> operator()(jni::JNIEnv& env, const double& value) const;
 };
 
 template <>
 struct Converter<jni::jdouble, float> {
-    Result<jni::jdouble> operator()(jni::JNIEnv&, const double& value) const {
-        return {(jni::jdouble) value};
-    }
+    Result<jni::jdouble> operator()(jni::JNIEnv&, const double& value) const;
 };
 
 /**
@@ -81,26 +61,17 @@ struct Converter<jni::jobject*, T, typename std::enable_if<std::is_integral<T>::
 
 template <>
 struct Converter<jni::jobject*, std::string> {
-    Result<jni::jobject*> operator()(jni::JNIEnv& env, const std::string& value) const {
-        return {jni::Make<jni::String>(env, value).Get()};
-    }
+    Result<jni::jobject*> operator()(jni::JNIEnv& env, const std::string& value) const;
 };
 
 template <>
 struct Converter<jni::jstring*, std::string> {
-    Result<jni::jstring*> operator()(jni::JNIEnv& env, const std::string& value) const {
-        return {jni::Make<jni::String>(env, value).Get()};
-    }
+    Result<jni::jstring*> operator()(jni::JNIEnv& env, const std::string& value) const;
 };
 
 template <>
 struct Converter<jni::jobject*, Color> {
-    Result<jni::jobject*> operator()(jni::JNIEnv& env, const Color& value) const {
-        std::stringstream sstream;
-        sstream << "rgba(" << value.r << ", " << value.g << ", " << value.b << ", "  << value.a << ")";
-        std::string result = sstream.str();
-        return convert<jni::jobject*, std::string>(env, result);
-    }
+    Result<jni::jobject*> operator()(jni::JNIEnv& env, const Color& value) const;
 };
 
 template <std::size_t N>
@@ -116,41 +87,19 @@ struct Converter<jni::jobject*, std::array<float, N>> {
 
 template <>
 struct Converter<jni::jobject*, std::vector<std::string>> {
-    Result<jni::jobject*> operator()(jni::JNIEnv& env, const std::vector<std::string>& value) const {
-        static jni::jclass* stringCass = jni::NewGlobalRef(env, &jni::FindClass(env, "java/lang/String")).release();
-        jni::jarray<jni::jobject>& jarray = jni::NewObjectArray(env, value.size(), *stringCass);
-
-        for(size_t i = 0; i < value.size(); i = i + 1) {
-            Result<jni::jobject*> converted = convert<jni::jobject*, std::string>(env, value.at(i));
-            jni::SetObjectArrayElement(env, jarray, i, *converted);
-        }
-
-        return &jarray;
-    }
+    Result<jni::jobject*> operator()(jni::JNIEnv& env, const std::vector<std::string>& value) const;
 };
 
 template <>
 struct Converter<jni::jobject*, std::vector<float>> {
-    Result<jni::jobject*> operator()(jni::JNIEnv& env, const std::vector<float>& value) const {
-        static jni::jclass* floatClass = jni::NewGlobalRef(env, &jni::FindClass(env, "java/lang/Float")).release();
-        jni::jarray<jni::jobject>& jarray = jni::NewObjectArray(env, value.size(), *floatClass);
-
-        for(size_t i = 0; i < value.size(); i = i + 1) {
-            Result<jni::jobject*> converted = convert<jni::jobject*, float>(env, value.at(i));
-            jni::SetObjectArrayElement(env, jarray, i, *converted);
-        }
-
-        return &jarray;
-    }
+    Result<jni::jobject*> operator()(jni::JNIEnv& env, const std::vector<float>& value) const;
 };
 
 // Java -> C++
 
 template <>
 struct Converter<std::string, jni::String> {
-    Result<std::string> operator()(jni::JNIEnv& env, const jni::String& value) const {
-        return { jni::Make<std::string>(env, value) };
-    }
+    Result<std::string> operator()(jni::JNIEnv& env, const jni::String& value) const;
 };
 
 } // namespace conversion
diff --git a/platform/android/src/geojson/conversion/feature.cpp b/platform/android/src/geojson/conversion/feature.cpp
new file mode 100644
index 0000000000..8dff05aa12
--- /dev/null
+++ b/platform/android/src/geojson/conversion/feature.cpp
@@ -0,0 +1,192 @@
+#include "feature.hpp"
+#include "geometry.hpp"
+
+#include "../../conversion/constant.hpp"
+#include "../../conversion/conversion.hpp"
+#include "../../jni/local_object.hpp"
+
+namespace mbgl {
+namespace android {
+namespace conversion {
+
+/**
+ * Turn feature identifier into std::string
+ */
+class FeatureIdVisitor {
+public:
+
+    template<class T>
+    std::string operator()(const T& i) const {
+        return std::to_string(i);
+    }
+
+    std::string operator()(const std::string& i) const {
+        return i;
+    }
+
+    std::string operator()(const std::nullptr_t&) const {
+        return "";
+    }
+
+};
+
+/**
+ * Turn properties into Java GSON JsonObject's
+ */
+class PropertyValueEvaluator {
+public:
+    jni::JNIEnv& env;
+
+    /**
+     * null
+     */
+    jni::jobject* operator()(const mapbox::geometry::null_value_t &) const {
+        return (jni::jobject*) nullptr;
+    }
+
+    /**
+     * Boolean primitive
+     */
+    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;
+    }
+
+    /**
+     * String primitive
+     */
+    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;
+    }
+
+    /**
+     * Number primitives
+     */
+    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;
+    }
+
+
+    /**
+     * Json Array
+     */
+    jni::jobject* operator()(const std::vector<mbgl::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, mbgl::Value::visit(v, *this));
+            jni::CallMethod<void>(env, jarray, *add, converted.get());
+        }
+
+        return jarray;
+    }
+
+    /**
+     * Json Object
+     */
+    jni::jobject* operator()(const std::unordered_map<std::string, mbgl::Value> &value) const {
+        // TODO: clean up duplication here
+        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;
+    }
+};
+
+Result<jni::jobject*> Converter<jni::jobject*, std::unordered_map<std::string, mbgl::Value>>::operator()(jni::JNIEnv& env, const std::unordered_map<std::string, mbgl::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
+    PropertyValueEvaluator evaluator {env};
+    for (auto &item : value) {
+        jni::LocalObject<jni::jobject> converted = jni::NewLocalObject(env, mbgl::Value::visit(item.second, evaluator));
+        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};
+}
+
+Result<jni::Object<android::geojson::Feature>> Converter<jni::Object<android::geojson::Feature>, mbgl::Feature>::operator()(jni::JNIEnv& env, const mbgl::Feature& value) const {
+
+    // Convert Id
+    FeatureIdVisitor idEvaluator;
+    std::string id = (value.id) ? mapbox::geometry::identifier::visit(value.id.value(), idEvaluator) : "";
+    auto jid = jni::Make<jni::String>(env, id);
+
+    // Convert properties
+    auto properties = jni::Object<gson::JsonObject>(*convert<jni::jobject*>(env, value.properties));
+
+    // Convert geometry
+    auto geometry = *convert<jni::Object<android::geojson::Geometry>>(env, value.geometry);
+
+    // Create feature
+    auto feature = android::geojson::Feature::fromGeometry(env, geometry, properties, jid);
+
+    //Cleanup
+    jni::DeleteLocalRef(env, jid);
+    jni::DeleteLocalRef(env, geometry);
+    jni::DeleteLocalRef(env, properties);
+
+    return feature;
+}
+
+Result<jni::Array<jni::Object<android::geojson::Feature>>> Converter<jni::Array<jni::Object<android::geojson::Feature>>, std::vector<mbgl::Feature>>::operator()(jni::JNIEnv& env, const std::vector<mbgl::Feature>& value) const {
+    using namespace mbgl::android::geojson;
+    auto features = jni::Array<jni::Object<Feature>>::New(env, value.size(), Feature::javaClass);
+
+    for(size_t i = 0; i < value.size(); i = i + 1) {
+        auto converted = *convert<jni::Object<android::geojson::Feature>, mbgl::Feature>(env, value.at(i));
+        features.Set(env, i, converted);
+        jni::DeleteLocalRef(env, converted);
+    }
+
+    return {features};
+}
+
+} // namespace conversion
+} // namespace android
+} // namespace mbgl
diff --git a/platform/android/src/geojson/conversion/feature.hpp b/platform/android/src/geojson/conversion/feature.hpp
index 8fc62a2789..031449cd23 100644
--- a/platform/android/src/geojson/conversion/feature.hpp
+++ b/platform/android/src/geojson/conversion/feature.hpp
@@ -1,215 +1,31 @@
 #pragma once
 
-#include "../../conversion/constant.hpp"
 #include "../../conversion/conversion.hpp"
-#include "geometry.hpp"
-#include "../../gson/json_object.hpp"
+#include "../feature.hpp"
 
 #include <mbgl/util/feature.hpp>
-#include <mapbox/variant.hpp>
-#include <mapbox/geometry.hpp>
-
 #include <jni/jni.hpp>
-#include "../../jni/local_object.hpp"
-#include "../feature.hpp"
 
-#include <string>
-#include <array>
 #include <vector>
-#include <sstream>
-
-#include <mbgl/util/logging.hpp>
+#include <unordered_map>
 
 namespace mbgl {
 namespace android {
 namespace conversion {
 
-/**
- * Turn feature identifier into std::string
- */
-class FeatureIdVisitor {
-public:
-
-    template<class T>
-    std::string operator()(const T& i) const {
-        return std::to_string(i);
-    }
-
-    std::string operator()(const std::string& i) const {
-        return i;
-    }
-
-    std::string operator()(const std::nullptr_t&) const {
-        return "";
-    }
-
-};
-
-/**
- * Turn properties into Java GSON JsonObject's
- */
-class PropertyValueEvaluator {
-public:
-    jni::JNIEnv& env;
-
-    /**
-     * null
-     */
-    jni::jobject* operator()(const mapbox::geometry::null_value_t &) const {
-        return (jni::jobject*) nullptr;
-    }
-
-    /**
-     * Boolean primitive
-     */
-    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;
-    }
-
-    /**
-     * String primitive
-     */
-    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;
-    }
-
-    /**
-     * Number primitives
-     */
-    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;
-    }
-
-
-    /**
-     * Json Array
-     */
-    jni::jobject* operator()(const std::vector<mbgl::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, mbgl::Value::visit(v, *this));
-            jni::CallMethod<void>(env, jarray, *add, converted.get());
-        }
-
-        return jarray;
-    }
-
-    /**
-     * Json Object
-     */
-    jni::jobject* operator()(const std::unordered_map<std::string, mbgl::Value> &value) const {
-        // TODO: clean up duplication here
-        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;
-    }
-};
-
 template <>
 struct Converter<jni::jobject*, std::unordered_map<std::string, mbgl::Value>> {
-    Result<jni::jobject*> operator()(jni::JNIEnv& env, const std::unordered_map<std::string, mbgl::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
-        PropertyValueEvaluator evaluator {env};
-        for (auto &item : value) {
-            jni::LocalObject<jni::jobject> converted = jni::NewLocalObject(env, mbgl::Value::visit(item.second, evaluator));
-            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};
-    }
+    Result<jni::jobject*> operator()(jni::JNIEnv& env, const std::unordered_map<std::string, mbgl::Value>& value) const;
 };
 
-
 template <>
 struct Converter<jni::Object<android::geojson::Feature>, mbgl::Feature> {
-    Result<jni::Object<android::geojson::Feature>> operator()(jni::JNIEnv& env, const mbgl::Feature& value) const {
-
-        // Convert Id
-        FeatureIdVisitor idEvaluator;
-        std::string id = (value.id) ? mapbox::geometry::identifier::visit(value.id.value(), idEvaluator) : "";
-        auto jid = jni::Make<jni::String>(env, id);
-
-        // Convert properties
-        auto properties = jni::Object<gson::JsonObject>(*convert<jni::jobject*>(env, value.properties));
-
-        // Convert geometry
-        auto geometry = *convert<jni::Object<android::geojson::Geometry>>(env, value.geometry);
-
-        // Create feature
-        auto feature = android::geojson::Feature::fromGeometry(env, geometry, properties, jid);
-
-        //Cleanup
-        jni::DeleteLocalRef(env, jid);
-        jni::DeleteLocalRef(env, geometry);
-        jni::DeleteLocalRef(env, properties);
-
-        return feature;
-    }
+    Result<jni::Object<android::geojson::Feature>> operator()(jni::JNIEnv& env, const mbgl::Feature& value) const;
 };
 
 template <>
 struct Converter<jni::Array<jni::Object<android::geojson::Feature>>, std::vector<mbgl::Feature>> {
-    Result<jni::Array<jni::Object<android::geojson::Feature>>> operator()(jni::JNIEnv& env, const std::vector<mbgl::Feature>& value) const {
-        using namespace mbgl::android::geojson;
-        auto features = jni::Array<jni::Object<Feature>>::New(env, value.size(), Feature::javaClass);
-
-        for(size_t i = 0; i < value.size(); i = i + 1) {
-            auto converted = *convert<jni::Object<android::geojson::Feature>, mbgl::Feature>(env, value.at(i));
-            features.Set(env, i, converted);
-            jni::DeleteLocalRef(env, converted);
-        }
-
-        return {features};
-    }
+    Result<jni::Array<jni::Object<android::geojson::Feature>>> operator()(jni::JNIEnv& env, const std::vector<mbgl::Feature>& value) const;
 };
 
 } // namespace conversion
diff --git a/platform/android/src/style/conversion/filter.cpp b/platform/android/src/style/conversion/filter.cpp
new file mode 100644
index 0000000000..4eac0cf82b
--- /dev/null
+++ b/platform/android/src/style/conversion/filter.cpp
@@ -0,0 +1,26 @@
+#include "filter.hpp"
+#include "../android_conversion.hpp"
+
+#include <mbgl/style/conversion.hpp>
+#include <mbgl/style/conversion/filter.hpp>
+
+namespace mbgl {
+namespace android {
+namespace conversion {
+
+optional<mbgl::style::Filter> toFilter(jni::JNIEnv& env, jni::Array<jni::Object<>> jfilter) {
+    mbgl::optional<mbgl::style::Filter> filter;
+    if (jfilter) {
+      mbgl::style::conversion::Error error;
+      auto converted = mbgl::style::conversion::convert<mbgl::style::Filter>(Value(env, jfilter), error);
+      if (!converted) {
+          mbgl::Log::Error(mbgl::Event::JNI, "Error converting filter: " + error.message);
+      }
+      filter = std::move(*converted);
+    }
+    return filter;
+}
+
+} // namespace conversion
+} // namespace android
+} // namespace mbgl
\ No newline at end of file
diff --git a/platform/android/src/style/conversion/filter.hpp b/platform/android/src/style/conversion/filter.hpp
index 241c98713a..df482de8f3 100644
--- a/platform/android/src/style/conversion/filter.hpp
+++ b/platform/android/src/style/conversion/filter.hpp
@@ -1,30 +1,15 @@
 #pragma once
 
-#include "../android_conversion.hpp"
-#include <mbgl/style/conversion/filter.hpp>
-#include <mbgl/style/conversion_impl.hpp>
+#include <mbgl/style/filter.hpp>
+#include <mbgl/util/optional.hpp>
 
 #include <jni/jni.hpp>
 
-#include <tuple>
-#include <map>
-
 namespace mbgl {
 namespace android {
 namespace conversion {
 
-inline optional<mbgl::style::Filter> toFilter(jni::JNIEnv& env, jni::Array<jni::Object<>> jfilter) {
-    mbgl::optional<mbgl::style::Filter> filter;
-    if (jfilter) {
-      mbgl::style::conversion::Error error;
-      auto converted = mbgl::style::conversion::convert<mbgl::style::Filter>(Value(env, jfilter), error);
-      if (!converted) {
-          mbgl::Log::Error(mbgl::Event::JNI, "Error converting filter: " + error.message);
-      }
-      filter = std::move(*converted);
-    }
-    return filter;
-}
+optional<mbgl::style::Filter> toFilter(jni::JNIEnv&, jni::Array<jni::Object<>>);
 
 } // namespace conversion
 } // namespace android
diff --git a/platform/android/src/style/conversion/position.cpp b/platform/android/src/style/conversion/position.cpp
new file mode 100644
index 0000000000..9b3925914e
--- /dev/null
+++ b/platform/android/src/style/conversion/position.cpp
@@ -0,0 +1,24 @@
+#include "position.hpp"
+
+namespace mbgl {
+namespace android {
+namespace conversion {
+
+Result<jni::Object<Position>> Converter<jni::Object<Position>, mbgl::style::Position>::operator()(jni::JNIEnv &env, const mbgl::style::Position &value) const {
+    std::array<float, 3> cartPosition = value.getSpherical();
+    return Position::fromPosition(env, cartPosition[0], cartPosition[1], cartPosition[2]);
+}
+
+Result<mbgl::style::Position> Converter<mbgl::style::Position, jni::Object<Position>>::operator()(jni::JNIEnv &env, const jni::Object<Position> &value) const {
+    float radialCoordinate = Position::getRadialCoordinate(env, value);
+    float azimuthalAngle = Position::getAzimuthalAngle(env, value);
+    float polarAngle = Position::getPolarAngle(env, value);
+    std::array<float, 3> cartPosition {{radialCoordinate, azimuthalAngle, polarAngle}};
+    mbgl::style::Position position{};
+    position.set(cartPosition);
+    return position;
+}
+
+}
+}
+}
diff --git a/platform/android/src/style/conversion/position.hpp b/platform/android/src/style/conversion/position.hpp
index f32a892c0c..2ef4bf4395 100644
--- a/platform/android/src/style/conversion/position.hpp
+++ b/platform/android/src/style/conversion/position.hpp
@@ -1,37 +1,25 @@
 #pragma once
 
 #include "../../conversion/conversion.hpp"
+#include "../position.hpp"
 
-#include <jni/jni.hpp>
 #include <mbgl/style/position.hpp>
-#include "../../jni/local_object.hpp"
-#include "../position.hpp"
+#include <jni/jni.hpp>
 
 namespace mbgl {
 namespace android {
 namespace conversion {
 
-template<>
+template <>
 struct Converter<jni::Object<Position>, mbgl::style::Position> {
-    Result<jni::Object<Position>> operator()(jni::JNIEnv &env, const mbgl::style::Position &value) const {
-        std::array<float, 3> cartPosition = value.getSpherical();
-        return Position::fromPosition(env, cartPosition[0], cartPosition[1], cartPosition[2]);
-    }
+    Result<jni::Object<Position>> operator()(jni::JNIEnv &env, const mbgl::style::Position &value) const;
 };
 
-template<>
+template <>
 struct Converter<mbgl::style::Position, jni::Object<Position>> {
-    Result<mbgl::style::Position> operator()(jni::JNIEnv &env, const jni::Object<Position> &value) const {
-        float radialCoordinate = Position::getRadialCoordinate(env, value);
-        float azimuthalAngle = Position::getAzimuthalAngle(env, value);
-        float polarAngle = Position::getPolarAngle(env, value);
-        std::array<float, 3> cartPosition {{radialCoordinate, azimuthalAngle, polarAngle}};
-        mbgl::style::Position position{};
-        position.set(cartPosition);
-        return position;
-    }
+    Result<mbgl::style::Position> operator()(jni::JNIEnv &env, const jni::Object<Position> &value) const;
 };
 
 }
 }
-}
\ No newline at end of file
+}
diff --git a/platform/android/src/style/conversion/property_expression.hpp b/platform/android/src/style/conversion/property_expression.hpp
index ae9d4ea41c..08429960cb 100644
--- a/platform/android/src/style/conversion/property_expression.hpp
+++ b/platform/android/src/style/conversion/property_expression.hpp
@@ -1,16 +1,11 @@
 #pragma once
 
-#include <mbgl/style/property_value.hpp>
 #include "../../conversion/conversion.hpp"
-#include "../../conversion/constant.hpp"
-#include "types.hpp"
-#include "../../java/lang.hpp"
-
-#include <jni/jni.hpp>
 #include "../../gson/json_element.hpp"
 
-#include <tuple>
-#include <map>
+#include <mbgl/style/property_expression.hpp>
+
+#include <jni/jni.hpp>
 
 namespace mbgl {
 namespace android {
@@ -18,11 +13,8 @@ namespace conversion {
 
 template <class T>
 struct Converter<jni::Object<android::gson::JsonElement>, mbgl::style::PropertyExpression<T>> {
-
     Result<jni::Object<android::gson::JsonElement>> operator()(jni::JNIEnv& env, const mbgl::style::PropertyExpression<T>& value) const {
-        // Convert expressions
-        mbgl::Value expressionValue = value.getExpression().serialize();
-        return gson::JsonElement::New(env, expressionValue);
+        return gson::JsonElement::New(env, value.getExpression().serialize());
     }
 };
 
diff --git a/platform/android/src/style/conversion/property_value.hpp b/platform/android/src/style/conversion/property_value.hpp
index 256647cddf..e4d8f59ec3 100644
--- a/platform/android/src/style/conversion/property_value.hpp
+++ b/platform/android/src/style/conversion/property_value.hpp
@@ -2,6 +2,7 @@
 
 #include <mbgl/style/color_ramp_property_value.hpp>
 #include <mbgl/style/property_value.hpp>
+
 #include "../../conversion/conversion.hpp"
 #include "../../conversion/constant.hpp"
 #include "property_expression.hpp"
@@ -17,25 +18,22 @@ namespace conversion {
 template <typename T>
 class PropertyValueEvaluator {
 public:
-
     PropertyValueEvaluator(jni::JNIEnv& _env) : env(_env) {}
 
     jni::jobject* operator()(const mbgl::style::Undefined) const {
         return nullptr;
     }
 
-    jni::jobject* operator()(const T &value) const {
-        Result<jni::jobject*> result = convert<jni::jobject*>(env, value);
-        return *result;
+    jni::jobject* operator()(const T& value) const {
+        return *convert<jni::jobject*>(env, value);
     }
 
-    jni::jobject* operator()(const mbgl::style::PropertyExpression<T> &value) const {
-        return *convert<jni::Object<android::gson::JsonElement>, mbgl::style::PropertyExpression<T>>(env, value);
+    jni::jobject* operator()(const mbgl::style::PropertyExpression<T>& value) const {
+        return *convert<jni::Object<android::gson::JsonElement>>(env, value);
     }
 
 private:
     jni::JNIEnv& env;
-
 };
 
 /**
@@ -43,7 +41,6 @@ private:
  */
 template <class T>
 struct Converter<jni::jobject*, mbgl::style::PropertyValue<T>> {
-
     Result<jni::jobject*> operator()(jni::JNIEnv& env, const mbgl::style::PropertyValue<T>& value) const {
         PropertyValueEvaluator<T> evaluator(env);
         return value.evaluate(evaluator);
@@ -55,8 +52,7 @@ struct Converter<jni::jobject*, mbgl::style::PropertyValue<T>> {
  */
 template <>
 struct Converter<jni::jobject*, mbgl::style::ColorRampPropertyValue> {
-
-    Result<jni::jobject*> operator()(jni::JNIEnv& env, const mbgl::style::ColorRampPropertyValue value) const {
+    Result<jni::jobject*> operator()(jni::JNIEnv& env, const mbgl::style::ColorRampPropertyValue& value) const {
         PropertyValueEvaluator<mbgl::style::ColorRampPropertyValue> evaluator(env);
         return *convert<jni::jobject*>(env, value.evaluate(evaluator));
     }
diff --git a/platform/android/src/style/conversion/transition_options.cpp b/platform/android/src/style/conversion/transition_options.cpp
new file mode 100644
index 0000000000..313333ad17
--- /dev/null
+++ b/platform/android/src/style/conversion/transition_options.cpp
@@ -0,0 +1,16 @@
+#include "transition_options.hpp"
+
+namespace mbgl {
+namespace android {
+namespace conversion {
+
+Result<jni::Object<TransitionOptions>> Converter<jni::Object<TransitionOptions>, mbgl::style::TransitionOptions>::operator()(jni::JNIEnv& env, const mbgl::style::TransitionOptions& value) const {
+    return TransitionOptions::fromTransitionOptions(env,
+        std::chrono::duration_cast<std::chrono::milliseconds>(value.duration.value_or(mbgl::Duration::zero())).count(),
+        std::chrono::duration_cast<std::chrono::milliseconds>(value.delay.value_or(mbgl::Duration::zero())).count()
+    );
+}
+
+}
+}
+}
diff --git a/platform/android/src/style/conversion/transition_options.hpp b/platform/android/src/style/conversion/transition_options.hpp
index ae65a32194..6630456d37 100644
--- a/platform/android/src/style/conversion/transition_options.hpp
+++ b/platform/android/src/style/conversion/transition_options.hpp
@@ -1,11 +1,11 @@
 #pragma once
 
 #include "../../conversion/conversion.hpp"
+#include "../transition_options.hpp"
 
-#include <jni/jni.hpp>
 #include <mbgl/style/transition_options.hpp>
-#include "../../jni/local_object.hpp"
-#include "../transition_options.hpp"
+
+#include <jni/jni.hpp>
 
 namespace mbgl {
 namespace android {
@@ -13,18 +13,9 @@ namespace conversion {
 
 template<>
 struct Converter<jni::Object<TransitionOptions>, mbgl::style::TransitionOptions> {
-    Result<jni::Object<TransitionOptions>> operator()(jni::JNIEnv &env, const mbgl::style::TransitionOptions &value) const {
-
-        // Convert duration
-        jlong duration =  std::chrono::duration_cast<std::chrono::milliseconds>(value.duration.value_or(mbgl::Duration::zero())).count();
-        // Convert delay
-        jlong delay = std::chrono::duration_cast<std::chrono::milliseconds>(value.delay.value_or(mbgl::Duration::zero())).count();
-
-        // Create transition options
-        return TransitionOptions::fromTransitionOptions(env, duration, delay);
-    }
+    Result<jni::Object<TransitionOptions>> operator()(jni::JNIEnv&, const mbgl::style::TransitionOptions&) const;
 };
 
 }
 }
-}
\ No newline at end of file
+}
diff --git a/platform/android/src/style/conversion/url_or_tileset.cpp b/platform/android/src/style/conversion/url_or_tileset.cpp
new file mode 100644
index 0000000000..2ec5856751
--- /dev/null
+++ b/platform/android/src/style/conversion/url_or_tileset.cpp
@@ -0,0 +1,30 @@
+#include "url_or_tileset.hpp"
+#include "../android_conversion.hpp"
+
+#include <mbgl/style/conversion.hpp>
+#include <mbgl/style/conversion/tileset.hpp>
+
+namespace mbgl {
+namespace android {
+
+// This conversion is expected not to fail because it's used only in contexts where
+// the value was originally a String or TileSet object on the Java side. If it fails
+// to convert, it's a bug in our serialization or Java-side static typing.
+variant<std::string, Tileset> convertURLOrTileset(mbgl::android::Value&& value) {
+    using namespace mbgl::style::conversion;
+
+    const Convertible convertible(std::move(value));
+    if (isObject(convertible)) {
+        Error error;
+        optional<Tileset> tileset = convert<Tileset>(convertible, error);
+        if (!tileset) {
+            throw std::logic_error(error.message);
+        }
+        return { *tileset };
+    } else {
+        return { *toString(convertible) };
+    }
+}
+
+}
+}
diff --git a/platform/android/src/style/conversion/url_or_tileset.hpp b/platform/android/src/style/conversion/url_or_tileset.hpp
index d6bf86639c..f42a9b9a2a 100644
--- a/platform/android/src/style/conversion/url_or_tileset.hpp
+++ b/platform/android/src/style/conversion/url_or_tileset.hpp
@@ -1,37 +1,16 @@
 #pragma once
 
-#include <mbgl/util/optional.hpp>
 #include <mbgl/util/variant.hpp>
-
 #include <mbgl/util/tileset.hpp>
-#include <mbgl/style/conversion/tileset.hpp>
-#include <mbgl/style/conversion_impl.hpp>
-
-#include <jni/jni.hpp>
 
 #include <string>
 
+#include "../value.hpp"
+
 namespace mbgl {
 namespace android {
 
-// This conversion is expected not to fail because it's used only in contexts where
-// the value was originally a String or TileSet object on the Java side. If it fails
-// to convert, it's a bug in our serialization or Java-side static typing.
-inline variant<std::string, Tileset> convertURLOrTileset(mbgl::android::Value&& value) {
-    using namespace mbgl::style::conversion;
-
-    const Convertible convertible(std::move(value));
-    if (isObject(convertible)) {
-        Error error;
-        optional<Tileset> tileset = convert<Tileset>(convertible, error);
-        if (!tileset) {
-            throw std::logic_error(error.message);
-        }
-        return { *tileset };
-    } else {
-        return { *toString(convertible) };
-    }
-}
+variant<std::string, Tileset> convertURLOrTileset(mbgl::android::Value&& value);
 
 }
 }