Converting an Application Module to a Library Module

JAR packages can be generated from both application modules and library modules. The process for converting an application module to a library module is straightforward.

Step 1: Modify the Build Configuration

Open your module's build.gradle file and locate the plugin declarasion at the top. Change:

apply plugin: 'com.android.application'

to:

apply plugin: 'com.android.library'

Step 2: Remove Application ID

Comment out or remove the applicationId line in your build.gradle file, as library modules do not require an application identifier.

Generating the JAR Package

Classic Approach (Pre-3.4.2)

Add the following task to the android block in your build.gradle file, alongside defaultConfig and buildTypes:

task extractJar(type: Copy) {
    delete 'build/libs/output.jar'
    from('build/intermediates/bundles/debug/')
    into('build/libs/')
    include('classes.jar')
    rename('classes.jar', 'output.jar')
}

extractJar.dependsOn(build)

Modern Approach (Android Studio 3.4.2+)

For newer versions, use the updated path:

task extractJar(type: Copy) {
    delete 'build/outputs/application.jar'
    from('build/intermediates/packaged-classes/release/')
    into('build/libs/')
    include('classes.jar')
    rename('classes.jar', 'application.jar')
}

extractJar.dependsOn(build)

Android Studio 4.0 and Above

For Studio 4.0 and newer versions, the intermediate path has changed:

task extractJar(type: Copy) {
    delete 'build/libs/module.jar'
    from('build/intermediates/aar_main_jar/release/')
    into('build/libs/')
    include('classes.jar')
    rename('classes.jar', 'module.jar')
}

extractJar.dependsOn(build)

Executing the Build Task

Command Line Method

Open a terminal in your project root directory and run:

./gradlew extractJar

Gradle Tool Window Method

Open the Gradle tool window in Android Studio, navigate to your module, then:

Tasks → build → extractJar

Double-click extractJar to execute the task. The generated JAR file will appear in the build/libs/ directory.

Task Configuration Notes

• The task name can be customized, but ensure consistency between task name and name.dependsOn(build)
• Adjust the source and destination paths according to your Android Studio version
• The output directory must exist or be created by the build process