We are working on a project that uses collada files. Our last resort is Unity 3d but that is heavier for the device. Is there anyway to use those files with android studio / java?
If you're asking about "using" collada files in terms of rendering them in your app, android runs OpenGL, so if you can set up a rendering context for that, you should be able to render a collada file (albeit with a bit more work than just using Unity).
Also see this post, with a similar question.