.obj to .j3o

Hello community

right now I’m creating an application to convert a obj file … to j3o.

the convert successful, but don’t create with the material (.mtl) the object is dark (attached image)

The code for the convert is:

model = refApp.getAssetManager().loadModel(files[i].getName());

            String nombre = files[i].getName();
            String[] nombresolo = nombre.split("\\.");

            File destDir = new File(nombreCarpetaj3o1);
            Path destPath = destDir.toPath();

            BinaryExporter exporter = BinaryExporter.getInstance();
            File file = new File(destPath + "/" + nombresolo[0] + ".j3o");
                exporter.save(model, file); //model is a Spatial 
            catch (IOException ex)
                System.out.println("exception: " + ex);

the model variable is a Spatial.

What is the problem?

Thank you