How to add library files in an Android studio

I'm going to use the Gson library to serialize/deserialize JSON objects in the Android studio. Library enclosures are not working. I created a new project and put the gson-2.2.3.jar file in the libs folder, added the library as a library, and compile files ('libs/gson-2.2.3.jar') in the gradle file, but when I build it, it says ClassDefNotFoundException... Why is it like this?