How to remedy error caused by guava: Program type already present: com.google.common.util.concurrent.internal.InternalFutures

An AAR library already uses com.google.guava.

If an app includes the following in its build.gradle:

api 'com.google.guava:guava:27.0-android'

Building the app generates the following error:

Execution failed for task ':app:transformDexArchiveWithExternalLibsDexMergerForDebug'.
> com.android.builder.dexing.DexArchiveMergerException: Error while merging dex archives: ...
  Learn how to resolve the issue at https://developer.android.com/studio/build/dependencies#duplicate_classes.
  Program type already present: com.google.common.util.concurrent.internal.InternalFutures

If I do not include "api 'com.google.guava:guava:27.0-android'", the app can be built, but it has runtime error of java.lang.NoClassDefFoundError when it reaches the point of using the Guava method: Iterables.find

Since Guava 27.0, ListenableFuture is located in separate artifact, see the announcement. You can try two things (one at a time):

1. Exclude "listenablefuture" module (group "com.google.guava") and build your project again.
2. I don't know the AAR specifics, but it could be that 27.0-android doesn't work with AAR, so you should try 26.0-android instead.