feat: Option to Select Language (Kotlin or Java) for Android Plugins (#122)

fabiomartino · OS-pedrogustavobilro · web-flow · commit 9861597b4e71 · 2026-03-02T10:57:58.000Z
* (feat) Add Kotlin/Java selectable choice * Updated dependencies * fix(android): Update dependencies to same versions as Cap 8 * chore(android): Set JVM 21 for Kotlin Since it's the recommended for Capacitor 8 References: https://capacitorjs.com/docs/updating/plugins/8-0#update-to-java-21-recommended * feat(android): Add kotlin version of test files And also support deleting them if the opposite language is selected. * chore: document android-lang as either-or, instead of e.g. To make it clearer that there are only two options. * chore: fix lint issues * fix: Add android-lang as CLI option Otherwise --android-lang is ignored and user needs to prompt it specifically * chore: minor changes on android language validation * chore(android): Kotlin option selected if not java Rather than using kotlin only if "kotlin" is returned --------- Co-authored-by: OS-pedrogustavobilro <pedro.gustavo.bilro@outsystems.com>
diff --git a/README.md b/README.md
@@ -30,4 +30,5 @@ As of the `0.8.0` release, example apps for testing are included when initializi
 --author <author> ......... Author name and email (e.g. "Name <name@example.com>")
 --license <id> ............ SPDX License ID (e.g. "MIT")
 --description <text> ...... Short description of plugin features
+--android-lang <text> ..... Language for Android plugin development (either "kotlin" or "java")
 ```
diff --git a/assets/plugin-template/README.md.mustache b/assets/plugin-template/README.md.mustache
@@ -4,8 +4,21 @@
 
 ## Install
 
+To use npm
+
 ```bash
 npm install {{{ PACKAGE_NAME }}}
+````
+
+To use yarn
+
+```bash
+yarn add {{{ PACKAGE_NAME }}}
+```
+
+Sync native files
+
+```bash
 npx cap sync
 ```
 
diff --git a/assets/plugin-template/android/build.gradle.mustache b/assets/plugin-template/android/build.gradle.mustache
@@ -3,19 +3,31 @@ ext {
     androidxAppCompatVersion = project.hasProperty('androidxAppCompatVersion') ? rootProject.ext.androidxAppCompatVersion : '1.7.1'
     androidxJunitVersion = project.hasProperty('androidxJunitVersion') ? rootProject.ext.androidxJunitVersion : '1.3.0'
     androidxEspressoCoreVersion = project.hasProperty('androidxEspressoCoreVersion') ? rootProject.ext.androidxEspressoCoreVersion : '3.7.0'
+{{ #KOTLIN }}
+    androidxCoreKTXVersion = project.hasProperty('androidxCoreKTXVersion') ? rootProject.ext.androidxCoreKTXVersion : '1.17.0'
+{{ /KOTLIN }}
 }
 
 buildscript {
+{{ #KOTLIN }}
+    ext.kotlin_version = project.hasProperty("kotlin_version") ? rootProject.ext.kotlin_version : '2.2.20'
+{{ /KOTLIN }}
     repositories {
         google()
         mavenCentral()
     }
     dependencies {
         classpath 'com.android.tools.build:gradle:8.13.0'
+{{ #KOTLIN }}
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+{{ /KOTLIN }}
     }
 }
 
 apply plugin: 'com.android.library'
+{{ #KOTLIN }}
+apply plugin: 'kotlin-android'
+{{ /KOTLIN }}
 
 android {
     namespace = "{{ PACKAGE_ID }}"
@@ -42,6 +54,12 @@ android {
     }
 }
 
+{{ #KOTLIN }}
+kotlin {
+    jvmToolchain(21)
+}
+{{ /KOTLIN }}
+
 repositories {
     google()
     mavenCentral()
@@ -52,6 +70,9 @@ dependencies {
     implementation fileTree(dir: 'libs', include: ['*.jar'])
     implementation project(':capacitor-android')
     implementation "androidx.appcompat:appcompat:$androidxAppCompatVersion"
+{{ #KOTLIN }}
+    implementation "androidx.core:core-ktx:$androidxCoreKTXVersion"
+{{ /KOTLIN }}
     testImplementation "junit:junit:$junitVersion"
     androidTestImplementation "androidx.test.ext:junit:$androidxJunitVersion"
     androidTestImplementation "androidx.test.espresso:espresso-core:$androidxEspressoCoreVersion"
diff --git a/assets/plugin-template/android/src/androidTest/kotlin/com/getcapacitor/android/ExampleInstrumentedTest.kt b/assets/plugin-template/android/src/androidTest/kotlin/com/getcapacitor/android/ExampleInstrumentedTest.kt
@@ -0,0 +1,26 @@
+package com.getcapacitor.android
+
+import android.content.Context
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import androidx.test.platform.app.InstrumentationRegistry
+import org.junit.Assert.assertEquals
+import org.junit.Test
+import org.junit.runner.RunWith
+
+/**
+ * Instrumented test, which will execute on an Android device.
+ *
+ * @see <a href="http://d.android.com/tools/testing">Testing documentation</a>
+ */
+@RunWith(AndroidJUnit4::class)
+class ExampleInstrumentedTest {
+
+    @Test
+    @Throws(Exception::class)
+    fun useAppContext() {
+        // Context of the app under test.
+        val appContext: Context = InstrumentationRegistry.getInstrumentation().targetContext
+
+        assertEquals("com.getcapacitor.android", appContext.packageName)
+    }
+}
diff --git a/assets/plugin-template/android/src/main/kotlin/__JAVA_PATH__.kt.mustache b/assets/plugin-template/android/src/main/kotlin/__JAVA_PATH__.kt.mustache
@@ -0,0 +1,12 @@
+package {{ PACKAGE_ID }}
+
+import android.util.Log
+
+class {{ CLASS }} {
+
+    fun echo(value: String?): String? {
+        Log.i("Echo", value ?: "null")
+
+        return value
+    }
+}
diff --git a/assets/plugin-template/android/src/main/kotlin/__JAVA_PATH__Plugin.kt.mustache b/assets/plugin-template/android/src/main/kotlin/__JAVA_PATH__Plugin.kt.mustache
@@ -0,0 +1,23 @@
+package {{ PACKAGE_ID }}
+
+import com.getcapacitor.JSObject
+import com.getcapacitor.Plugin
+import com.getcapacitor.PluginCall
+import com.getcapacitor.annotation.CapacitorPlugin
+import com.getcapacitor.PluginMethod
+
+@CapacitorPlugin(name = "{{ CLASS }}")
+class {{ CLASS }}Plugin : Plugin() {
+
+    private val implementation = {{ CLASS }}()
+
+    @PluginMethod
+    fun echo(call: PluginCall) {
+        val value = call.getString("value")
+
+        val ret = JSObject().apply {
+            put("value", implementation.echo(value))
+        }
+        call.resolve(ret)
+    }
+}
diff --git a/assets/plugin-template/android/src/test/kotlin/com/getcapacitor/ExampleUnitTest.kt b/assets/plugin-template/android/src/test/kotlin/com/getcapacitor/ExampleUnitTest.kt
@@ -0,0 +1,18 @@
+package com.getcapacitor
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+/**
+ * Example local unit test, which will execute on the development machine (host).
+ *
+ * @see <a href="http://d.android.com/tools/testing">Testing documentation</a>
+ */
+class ExampleUnitTest {
+
+    @Test
+    @Throws(Exception::class)
+    fun addition_isCorrect() {
+        assertEquals(4, 2 + 2)
+    }
+}
diff --git a/src/help.ts b/src/help.ts
@@ -10,6 +10,7 @@ const help = `
     --author <author> ......... Author name and email (e.g. "Name <name@example.com>")
     --license <id> ............ SPDX License ID (e.g. "MIT")
     --description <text> ...... Short description of plugin features
+    --android-lang ............ Language for Android plugin development (either "kotlin" or "java")
 
     -h, --help ................ Print help, then quit
     --verbose ................. Print verbose output to stderr
diff --git a/src/options.ts b/src/options.ts
@@ -17,6 +17,7 @@ export interface OptionValues {
   author: string;
   license: string;
   description: string;
+  'android-lang': string;
 }
 
 export type Validators = {
@@ -25,7 +26,16 @@ export type Validators = {
 
 const CLI_ARGS = ['dir'] as const;
 
-const CLI_OPTIONS = ['name', 'package-id', 'class-name', 'repo', 'author', 'license', 'description'] as const;
+const CLI_OPTIONS = [
+  'name',
+  'package-id',
+  'class-name',
+  'repo',
+  'author',
+  'license',
+  'description',
+  'android-lang',
+] as const;
 
 export const VALIDATORS: Validators = {
   name: (value) =>
@@ -57,6 +67,10 @@ export const VALIDATORS: Validators = {
     typeof value !== 'string' || value.trim().length === 0 ? `Must provide a valid license, e.g. "MIT"` : true,
   description: (value) =>
     typeof value !== 'string' || value.trim().length === 0 ? `Must provide a description` : true,
+  'android-lang': (value) =>
+    typeof value === 'string' && value.trim().length > 0 && /^(kotlin|kt|java)$/i.test(value)
+      ? true
+      : `Must be either "kotlin" or "java"`,
   dir: (value) =>
     typeof value !== 'string' || value.trim().length === 0
       ? `Must provide a directory, e.g. "my-plugin"`
diff --git a/src/prompt.ts b/src/prompt.ts
@@ -81,6 +81,15 @@ export const gatherDetails = (initialOptions: Options): Promise<OptionValues> =>
         message: `Enter a SPDX license identifier for your plugin.\n`,
         validate: VALIDATORS.license,
       },
+      {
+        type: 'select',
+        name: 'android-lang',
+        message: `What language would you like to use for your Android plugin?\n`,
+        choices: [
+          { title: 'Kotlin', value: 'kotlin' },
+          { title: 'Java', value: 'java' },
+        ],
+      },
       {
         type: 'text',
         name: 'description',
diff --git a/src/template.ts b/src/template.ts
@@ -1,4 +1,4 @@
-import { readFile, rmdir, mkdir, writeFile, unlink } from 'fs/promises';
+import { readFile, mkdir, writeFile, unlink, readdir, rm } from 'fs/promises';
 import Mustache from 'mustache';
 import { dirname, join, resolve, sep } from 'path';
 import { extract } from 'tar';
@@ -25,6 +25,7 @@ export const extractTemplate = async (
 ): Promise<void> => {
   const templateFiles: string[] = [];
   const templateFolders: string[] = [];
+  const androidLang = details['android-lang'].toLowerCase();
   await mkdir(dir, { recursive: true });
   await extract({
     file: type === 'PLUGIN_TEMPLATE' ? TEMPLATE_PATH : WWW_TEMPLATE_PATH,
@@ -41,14 +42,57 @@ export const extractTemplate = async (
   });
 
   await Promise.all(templateFiles.map((p) => resolve(dir, p)).map((p) => applyTemplate(p, details)));
-  await Promise.all(templateFolders.map((p) => resolve(dir, p)).map((p) => rmdir(p)));
+  await deleteUnnecessaryFolders(dir, androidLang);
+  await Promise.all(templateFolders.map((p) => resolve(dir, p)).map((p) => rm(p, { recursive: true })));
+};
+
+const deleteUnnecessaryFolders = async (dir: string, androidLang: string): Promise<void> => {
+  const androidSrcDir = join(dir, 'android', 'src');
+  const sourceSets = ['main', 'test', 'androidTest'];
+
+  for (const sourceSet of sourceSets) {
+    const sourceFolder = join(androidSrcDir, sourceSet);
+    const javaFolder = join(sourceFolder, 'java');
+    const kotlinFolder = join(sourceFolder, 'kotlin');
+
+    if (androidLang === 'kotlin' && (await folderExists(javaFolder))) {
+      await rm(javaFolder, { recursive: true });
+    }
+
+    if (androidLang === 'java' && (await folderExists(kotlinFolder))) {
+      await rm(kotlinFolder, { recursive: true });
+    }
+  }
+};
+
+const folderExists = async (folderPath: string): Promise<boolean> => {
+  try {
+    const files = await readdir(folderPath);
+    return files != null;
+  } catch (err) {
+    return false;
+  }
 };
 
 export const applyTemplate = async (
   p: string,
-  { name, 'package-id': packageId, 'class-name': className, repo, author, license, description }: OptionValues,
+  {
+    name,
+    'package-id': packageId,
+    'class-name': className,
+    repo,
+    author,
+    license,
+    description,
+    'android-lang': androidLang,
+  }: OptionValues,
 ): Promise<void> => {
   const template = await readFile(p, { encoding: 'utf8' });
+
+  const conditionalView = {
+    KOTLIN: androidLang.toLowerCase() !== 'java',
+  };
+
   const view = {
     CAPACITOR_VERSION: CAPACITOR_VERSION,
     PACKAGE_NAME: name,
@@ -60,17 +104,21 @@ export const applyTemplate = async (
     AUTHOR: author,
     LICENSE: license,
     DESCRIPTION: description,
+    ANDROID_LANG: androidLang,
   };
 
-  const contents = Mustache.render(template, view);
-  const filePath = Object.entries(view).reduce(
-    (acc, [key, value]) => (value ? acc.replaceAll(`__${key}__`, value) : acc),
-    p.substring(0, p.length - MUSTACHE_EXTENSION.length),
+  const combinedView = { ...view, ...conditionalView };
+  const intermediateContents = Mustache.render(template, combinedView);
+  const finalContents = Mustache.render(intermediateContents, view);
+  let filePath = p.substring(0, p.length - MUSTACHE_EXTENSION.length);
+  filePath = Object.entries(view).reduce(
+    (acc, [key, value]) => (value ? acc.replaceAll(`__${key}__`, value.toString()) : acc),
+    filePath,
   );
 
   await mkdir(dirname(filePath), { recursive: true });
   // take off the .mustache extension and write the file, then remove the template
-  await writeFile(filePath, contents, { encoding: 'utf8' });
+  await writeFile(filePath, finalContents, { encoding: 'utf8' });
 
   await unlink(p);
 };
