perf: Migrate Java to Kotlin by bensonarafat · Pull Request #842 · flutter-ml/google_ml_kit_flutter

bensonarafat · 2026-02-09T19:10:09Z

No description provided.

fbernaly · 2026-02-10T23:57:34Z

@bensonarafat : have only the Java -> Kotlin migration in this PR, remove all the Pigeon for code gen. Also, have only one plugin google_mlkit_commons, I would like to test that isolated and then extending teh changes to the other plugins. I prefer proceeding with this changes with caution to avoid breaking things.

bensonarafat · 2026-02-11T00:14:24Z

great

bensonarafat · 2026-02-11T01:35:37Z

@fbernaly
this is now ready for review

fbernaly · 2026-02-11T01:53:11Z

could you remove these files and make it only for google_mlkit_commons

bensonarafat · 2026-02-11T08:29:34Z

done @fbernaly

Copilot

Pull request overview

This PR migrates the Android codebase in the google_mlkit_commons package from Java to Kotlin. The migration includes three main classes: InputImageConverter, GoogleMlKitCommonsPlugin, and GenericModelManager. The PR also adds Kotlin support to the build configuration and updates the Gradle wrapper to a milestone version.

Changes:

Converted three Java classes to Kotlin equivalents maintaining the same functionality
Added Kotlin plugin and configuration to build.gradle
Updated Gradle wrapper to version 9.0-milestone-1

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 15 comments.

Show a summary per file

File	Description
packages/google_mlkit_commons/android/src/main/kotlin/com/google_mlkit_commons/InputImageConverter.kt	New Kotlin version of InputImageConverter with image processing logic
packages/google_mlkit_commons/android/src/main/kotlin/com/google_mlkit_commons/GoogleMlKitCommonsPlugin.kt	New Kotlin version of GoogleMlKitCommonsPlugin for Flutter integration
packages/google_mlkit_commons/android/src/main/kotlin/com/google_mlkit_commons/GenericModelManager.kt	New Kotlin version of GenericModelManager for ML model management
packages/google_mlkit_commons/android/src/main/java/com/google_mlkit_commons/InputImageConverter.java	Deleted original Java file
packages/google_mlkit_commons/android/src/main/java/com/google_mlkit_commons/GoogleMlKitCommonsPlugin.java	Deleted original Java file
packages/google_mlkit_commons/android/src/main/java/com/google_mlkit_commons/GenericModelManager.java	Deleted original Java file
packages/google_mlkit_commons/android/build.gradle	Added Kotlin plugin and configuration
packages/google_mlkit_commons/android/gradle/wrapper/gradle-wrapper.properties	Updated Gradle version to 9.0-milestone-1
packages/example/pubspec.lock	Minor dependency version updates

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Copilot · 2026-02-17T21:32:52Z

+
+            val height = metaData["height"]?.toString()?.toDouble()?.toInt() ?: throw IllegalArgumentException("Height is null")
+
+            if (imageFormat == ImageFormat.NV16 || imageFormat == ImageFormat.YV12) {


The image format check has been changed from ImageFormat.NV21 (in the original Java code) to ImageFormat.NV16. This is likely a typo that changes the behavior of the code. The original Java code checked for NV21 format, which is a common YUV format used in Android camera preview, whereas NV16 is less commonly used. This change may cause previously supported image formats to fail validation.

Suggested change

if (imageFormat == ImageFormat.NV16 || imageFormat == ImageFormat.YV12) {

if (imageFormat == ImageFormat.NV21 || imageFormat == ImageFormat.YV12) {

Copilot · 2026-02-17T21:32:52Z

+        result: MethodChannel.Result
+    ): InputImage? {
+        return try {
+            val path = imageData["path"] as? String


The path variable could be null (using safe cast as?), but it's passed directly to File() without null checking. If the path is null, this will throw a NullPointerException. Consider adding a null check or using the elvis operator to handle the null case explicitly.

Suggested change

val path = imageData["path"] as? String

val path = imageData["path"] as? String

if (path == null) {

result.error(

"InputImageConverterError",

"Image path is null or invalid",

null

)

return null

}

Copilot · 2026-02-17T21:32:52Z

+import com.google.mlkit.common.model.RemoteModelManager
+import io.flutter.plugin.common.MethodCall
+import io.flutter.plugin.common.MethodChannel
+import java.lang.reflect.Method


The import java.lang.reflect.Method on line 8 is unused and should be removed. This import is not present in the original Java code and appears to have been added by mistake.

Suggested change

import java.lang.reflect.Method

Copilot · 2026-02-17T21:32:53Z

@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.0-milestone-1-bin.zip


The gradle-wrapper.properties file specifies Gradle version 9.0-milestone-1, which is a pre-release milestone version. Using milestone (pre-release) versions in production code can introduce instability and potential compatibility issues. Consider using a stable release version of Gradle instead, such as 8.x or waiting for the stable 9.0 release.

Suggested change

distributionUrl=https\://services.gradle.org/distributions/gradle-9.0-milestone-1-bin.zip

distributionUrl=https\://services.gradle.org/distributions/gradle-8.10-bin.zip

Copilot · 2026-02-17T21:32:53Z

+                object: CheckModelIsDownloadedCallback {
+                    override fun onCheckResult (isDownloaded: Boolean?) {
+                        result.success(isDownloaded)
+                    }
+
+                    override  fun onError(e: Exception) {
+                        result.error("error", e.toString(), null)
+                    }
+                }
+            )
+            else -> result.notImplemented()
+        }
+    }
+
+    fun downloadModel (
+        remoteModel: RemoteModel,
+        downloadConditions: DownloadConditions,
+        result: MethodChannel.Result
+    ) {
+        isModelDownloaded(
+            remoteModel,
+            object: CheckModelIsDownloadedCallback {
+                override fun onCheckResult(isDownloaded: Boolean?) {
+                    if (isDownloaded == true) {
+                        result.success("success")
+                        return
+                    }
+
+                    remoteModelManager.download(remoteModel, downloadConditions)
+                        .addOnSuccessListener { result.success("success") }
+                        .addOnFailureListener { exception ->  result.error("error", exception.toString(), null) }
+
+                }
+
+                override fun onError(e: Exception) {
+                    result.error("error", e.toString(), null)
+                }
+            }
+        )
+    }
+
+
+    fun isModelDownloaded (model: RemoteModel, callback: CheckModelIsDownloadedCallback) {
+        try {
+            remoteModelManager.isModelDownloaded(model)
+                .addOnFailureListener { exception ->  callback.onError(exception) }
+                .addOnSuccessListener { isModelDownloaded -> callback.onCheckResult(isModelDownloaded) }
+        } catch (e: Exception) {
+            callback.onError(e)
+        }
+    }
+
+    fun deleteModel(remoteModel: RemoteModel, result: MethodChannel.Result) {
+        isModelDownloaded(
+            remoteModel,
+            object: CheckModelIsDownloadedCallback {


The object: syntax should have a space after the colon in Kotlin. Standard Kotlin formatting is object : CheckModelIsDownloadedCallback with a space after the colon. This applies to all three instances in this file (lines 47, 68, and 102).

Copilot · 2026-02-17T21:32:54Z

+    }
+
+    override fun onDetachedFromEngine(binding: FlutterPlugin.FlutterPluginBinding) {
+       channel.setMethodCallHandler(null)


There is inconsistent indentation on line 20. The line uses 7 spaces for indentation instead of the standard 8 spaces (or 2 tab stops) used elsewhere in the file. This should be corrected to match the indentation of other lines at the same scope level.

Suggested change

channel.setMethodCallHandler(null)

channel.setMethodCallHandler(null)

Copilot · 2026-02-17T21:32:54Z

+                        bitmapData.size
+                    )
+                    if (bitmap == null) {
+                        result. error(


There is extra whitespace before the dot operator in result. error. This should be result.error without the space to maintain consistent code style.

Suggested change

result. error(

result.error(

Copilot · 2026-02-17T21:32:55Z

+
+class GenericModelManager {
+
+    interface  CheckModelIsDownloadedCallback {


There is an extra space in the interface declaration between interface and CheckModelIsDownloadedCallback. The formatting should be interface CheckModelIsDownloadedCallback without the extra space.

Suggested change

interface CheckModelIsDownloadedCallback {

interface CheckModelIsDownloadedCallback {

Copilot · 2026-02-17T21:32:55Z

+                        .addOnFailureListener { exception ->  result.error("error", exception.toString(), null) }
+
+                }
+
+                override fun onError(e: Exception) {
+                    result.error("error", e.toString(), null)
+                }
+            }
+        )
+    }
+
+
+    fun isModelDownloaded (model: RemoteModel, callback: CheckModelIsDownloadedCallback) {
+        try {
+            remoteModelManager.isModelDownloaded(model)
+                .addOnFailureListener { exception ->  callback.onError(exception) }


There is inconsistent spacing in the lambda expressions. Lines 77 and 92 have two spaces after the arrow -> instead of one, which is inconsistent with the rest of the code. The spacing should be standardized to one space after the arrow operator.

Copilot · 2026-02-17T21:32:55Z

+import io.flutter.plugin.common.MethodCall
+import io.flutter.plugin.common.MethodChannel
+
+class GoogleMlKitCommonsPlugin: FlutterPlugin, MethodChannel.MethodCallHandler {


There is a missing space after the colon in the class declaration class GoogleMlKitCommonsPlugin:. Standard Kotlin formatting requires a space after the colon when declaring interfaces/superclasses, e.g., class GoogleMlKitCommonsPlugin : FlutterPlugin, MethodChannel.MethodCallHandler.

Suggested change

class GoogleMlKitCommonsPlugin: FlutterPlugin, MethodChannel.MethodCallHandler {

class GoogleMlKitCommonsPlugin : FlutterPlugin, MethodChannel.MethodCallHandler {

fbernaly · 2026-02-17T23:30:08Z

@bensonarafat : the PR had a lot of lint warning.

I added: ./scripts/analyze.sh, let's run that before sending a new PR and make sure to resolve all the lint warning, that makes the code beautiful and more maintainable.

bensonarafat added 2 commits February 9, 2026 20:09

perf: use pigeon for code gen

e8f7ad9

Update the common package

670c5b2

bensonarafat changed the title ~~perf: use pigeon for code gen~~ perf: Migrate Java to Kotlin and use Pigeon Code Gen Feb 10, 2026

pref: Remove pigeon changes and keep kotlin migration

23cebc5

bensonarafat changed the title ~~perf: Migrate Java to Kotlin and use Pigeon Code Gen~~ perf: Migrate Java to Kotlin Feb 11, 2026

fix: calling the static method from mlkit_common

f35eb55

bensonarafat marked this pull request as ready for review February 11, 2026 01:35

bensonarafat added 2 commits February 11, 2026 09:12

Remove translation changes

84e87de

fix: code indetent

97b06c5

fbernaly requested a review from Copilot February 17, 2026 21:27

Copilot started reviewing on behalf of fbernaly February 17, 2026 21:28 View session

fbernaly changed the base branch from develop to test February 17, 2026 21:30

Copilot AI reviewed Feb 17, 2026

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fbernaly approved these changes Feb 17, 2026

View reviewed changes

fbernaly merged commit 5aa67b8 into flutter-ml:test Feb 17, 2026
9 checks passed

fbernaly pushed a commit that referenced this pull request Feb 17, 2026

refactor: Migrate google_mlkit_commons from Java to Kotlin (#842)

2eafd22

fbernaly pushed a commit that referenced this pull request Feb 17, 2026

refactor: Migrate google_mlkit_commons from Java to Kotlin (#842)

619dd8e

bensonarafat deleted the pigeon branch February 18, 2026 14:20


		val height = metaData["height"]?.toString()?.toDouble()?.toInt() ?: throw IllegalArgumentException("Height is null")

		if (imageFormat == ImageFormat.NV16 \|\| imageFormat == ImageFormat.YV12) {

	if (imageFormat == ImageFormat.NV16 \|\| imageFormat == ImageFormat.YV12) {
	if (imageFormat == ImageFormat.NV21 \|\| imageFormat == ImageFormat.YV12) {

-            val path = imageData["path"] as? String
+            val path = imageData["path"] as? String
+            if (path == null) {
+                result.error(
+                    "InputImageConverterError",
+                    "Image path is null or invalid",
+                    null
+                )
+                return null
+            }

	distributionUrl=https\://services.gradle.org/distributions/gradle-9.0-milestone-1-bin.zip
	distributionUrl=https\://services.gradle.org/distributions/gradle-8.10-bin.zip

	channel.setMethodCallHandler(null)
	channel.setMethodCallHandler(null)


		class GenericModelManager {

		interface CheckModelIsDownloadedCallback {

	class GoogleMlKitCommonsPlugin: FlutterPlugin, MethodChannel.MethodCallHandler {
	class GoogleMlKitCommonsPlugin : FlutterPlugin, MethodChannel.MethodCallHandler {

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bensonarafat commented Feb 9, 2026

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bensonarafat commented Feb 11, 2026

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fbernaly commented Feb 17, 2026

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fbernaly commented Feb 11, 2026 •

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