How can I remove a library from the aar using gradle? - unity3d

Question

I'm currently building an android plugin for Unity. Because of that I need to include unity's classes.jar, which provides me with some methods in the com.unity3d.player package.
However when i do ./gradlew assemble it also packages the classes.jar into the .aar file under libs/classes.jar.
Now when I add this .aar to Unity and try to build, I get the following error:
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/player/a$1;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/player/a$2;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/player/a$a;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/player/a;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/player/b$1;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/player/b$2;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/player/b;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/player/c;
Uncaught translation error: java.lang.IllegalArgumentException: already added: Lcom/unity3d/player/d$1;
UNEXPECTED TOP-LEVEL EXCEPTION:
java.lang.RuntimeException: Translation has been interrupted
at com.android.dx.command.dexer.Main.processAllFiles(Main.java:608)
at com.android.dx.command.dexer.Main.runMonoDex(Main.java:311)
at com.android.dx.command.dexer.Main.run(Main.java:277)
at com.android.dx.command.dexer.Main.main(Main.java:245)
at com.android.dx.command.Main.main(Main.java:106)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at SDKMain.main(SDKMain.java:129)
Unity tries to add the classes.jar to it's android build again, but because the classes.jar is already in the .aar, this fails.
How can I exclude the classes.jar from the .aar?
EDIT
This is what I can do with the command line to remove the classes.jar
zip --delete tapfortapunity-release.aar "libs/*"
How do I call this with gradle?

Answer 1

UPDATE: I just found out that this problem solves itself if I just remove the unity.jar dependency from my build.gradle file:
//dependencies {
// compile files('src/main/libs/unity.jar')
//}
(the code compiles just fine, strangely, and no unity.jar in the .aar file...).
(just noticed that the code compiled because there was no reference to UnityPlayer* stuff...)
Same issue here. I browsed a bit and it seems like there is no clean way to solve the problem (yet!), so I guess it all boils down to this:
create a chain of tasks for the installation of your unity plugin (a task to create the Plugin/Android directory for instance, one to Copy the AAR file and native libraries, if any, etc)
remove the file from the zip using a task the previous one will dependsOn
Step 2 can be carried out in one of those following ways:
create an Exec task that will just execute the command you pointed out (this is probably what I'll end up doing, as I'm not really proficient with gradle...). Easy but not portable (relies on an extra utility).
create a JavaExectask and use Java7 support for zips to remove the entry (probably the best solution, but I don't really have much experience here).
try creating a new jar using the suggestion pointed out in this post: Post on gradle-user describing how to create a jar (or aar...) using gradle as Gradle supports zip files, but cannot change them in place (which implies it cannot remove stuff from them). Harder, but will not rely on external tools, so you'll get portability as a result.
It might not be an elegant solution and probably better ones exist, but it's a very simple, and works well
Hope this helps