How do I resolve “Duplicate files copied in APK META-INF/*”

I am working at a commercial android application. I am also using some libraries licensed under different license types some of them stating the following:

If the library has a “NOTICE” file with attribution notes, you must include that NOTICE when you distribute

(One of them is licensed under Apache License 2.0 for example).

There is more than one library. When I do the build with gradle or with Android Studio I obtain the following build error:

* What went wrong:
Execution failed for task ':app:transformResourcesWithMergeJavaResForDebug'.
> com.android.build.api.transform.TransformException: com.android.builder.packaging.DuplicateFileException: Duplicate files copied in APK META-INF/license.txt

The answers that I found until now on the internet and stackoverflow suggest to remove the license.txt(notice.txt or other files that could interfere like this) from packaging by adding to build.gradle file the following:

packagingOptions {
    exclude 'META-INF/DEPENDENCIES.txt'
    exclude 'META-INF/LICENSE.txt'
    exclude 'META-INF/NOTICE.txt'
    exclude 'META-INF/NOTICE'
    exclude 'META-INF/LICENSE'
    exclude 'META-INF/DEPENDENCIES'
    exclude 'META-INF/notice.txt'
    exclude 'META-INF/license.txt'
    exclude 'META-INF/dependencies.txt'
    exclude 'META-INF/LGPL2.1'
}

See for example: Android Studio 0.4 Duplicate files copied in APK META-INF/LICENSE.txt

According to the license of those libraries(Apache License 2.0 for instance), the license and notice files should be included.

My question: How can I add multiple files related to licensing(such as license.txt, notice.txt etc) from gradle into my project in order to be compliant with the licenses(technical detail: licences texts will be concatenated)?

Answer

There is a solution if you have only one license using the name license.txt (read: all license.txt copies are identical):

packagingOptions {
   pickFirst  'META-INF/license.txt'
}

Otherwise, Google also released a Gradle plugin to manage dependencies licenses. See here. I didn’t try it, but it looks like it’s capable of aggregating every dependency, and even generating an activity displaying all of those licenses.

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Answer