Calculate FFT from audio file

Before, I asked question about Get frequency wav audio using FFT and Complex class ,

There, I need to calculate FFT value from AudioRecord input --> from microphone , I somehow managed to get the FFT value...

Now I need to calculate FFT value from *.wav audio file that I saved before, I saved the audio in 'raw' folder inside 'res' folder from my project

I still using the same FFT Class: http://www.cs.princeton.edu/introcs/97data/FFT.java

The complex class to go with it: http://introcs.cs.princeton.edu/java/97data/Complex.java.html

I use this method to read audio file from my raw foldern, then I call method calculateFFT to go with it

private static final int RECORDER_BPP = 16;
  private static final int RECORDER_SAMPLERATE = 44100;
  private static final int RECORDER_CHANNELS = AudioFormat.CHANNEL_IN_STEREO;
  private static final int RECORDER_AUDIO_ENCODING = AudioFormat.ENCODING_PCM_16BIT;


private void asli(){

            int counter = 0;
            int data;
            InputStream inputStream  = getResources().openRawResource(R.raw.b1);
            DataInputStream dataInputStream = new DataInputStream(inputStream);
            List<Integer> content = new ArrayList<Integer>(); 

            try {
                while ((data = dataInputStream.read()) != -1) {
                    content.add(data);
                    counter++; }
            } catch (IOException e) {
                e.printStackTrace();}

                int[] b = new int[content.size()];
                int cont = 0;
                byte[] audio = convertArray(b);
        }

Method to convert to byte

public