Add a jar

Right click on the project. Select Open Module Settings, click Libraries then the + button. A file chooser window should open where you select the jar file. Finally clean the project from the command line e.g:

gradle clean

Original article copied from StackOverflow

From ar as library`_

I’ve been struggling with the same thing for many hours, trying to get the Gson jar to work no less. I finally cracked it – here are the steps I took:

Put the Gson jar (in my case, gson-2.2.4.jar) into the libs folder

Right click it and hit Add as library

Ensure that compile files(libs/gson-2.2.4.jar) is in your build.gradle file

Do a clean build (you can probably do this fine in Android Studio, but to make sure I navigated in a terminal to the root folder of my app and typed gradlew clean. I’m on Mac OS X, the command might be different on your system

After I did the above three, it started working fine. I think the Add as library step was the one I’d previously missed, and it didn’t work until I cleaned it either.