Convert an existing Flutter Kotlin project to Flutter Java project

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I created a Flutter project using default values, which are Kotlin for Android and Swift for iOS. Halfway through the project I needed to integrate a 3rd party Android SDK that requires Java. Can I convert a Flutter project to Java for Android after creation?

I know I will need yo use Platform Channels to integrate native code with my Flutter app, this is not my concern.

Answer

I had the same problem, for me this solution works.

  1. Move folder com.example.test_app (any name you have) from android/app/src/main/kotlin -> android/app/src/main/java
  2. Replace MainActivity.kt with Java version, or copy down here

    package com.example.test_app;
    
    import androidx.annotation.NonNull;
    import io.flutter.embedding.android.FlutterActivity;
    import io.flutter.embedding.engine.FlutterEngine;
    import io.flutter.plugins.GeneratedPluginRegistrant;
    
    public class MainActivity extends FlutterActivity {
     @Override
     public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) {
     GeneratedPluginRegistrant.registerWith(flutterEngine);
     }
    }
    
  3. Remove following code android/app/build.grandle

    ...
    apply plugin: 'kotlin-android'
    ...
    sourceSets {
        main.java.srcDirs += 'src/main/kotlin'
    }
    
  4. In the same place replace following:

    dependencies {
        implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
        testImplementation 'junit:junit:4.12'
        androidTestImplementation 'androidx.test:runner:1.1.0'
        androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.0'
    }
    

    to

    dependencies {
        testImplementation 'junit:junit:4.12'
        androidTestImplementation 'com.android.support.test:runner:1.0.2'
        androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
    }
    


Source: stackoverflow