GUI goes blank while an mp3 file is being played

NOTE: I accidentally asked this question in the wrong category first. So that question is 250 points on top of this 50 for this one.

I am building a little Java program that will play mp3s. With my current coding, the mp3s play just fine, the only thing is that while an mp3 is playing, the GUI goes completely blank until the mp3 is finished playing. Why would this happen and what do i do to fix it?  I have pasted the code to play the mp3s below.  Thank you!

public void testPlay(String filename)
{
System.out.println("testPlay started");
  try {
    File file = new File(filename);
    AudioInputStream in= AudioSystem.getAudioInputStream(file);
    AudioInputStream din = null;
    AudioFormat baseFormat = in.getFormat();
    AudioFormat decodedFormat = new AudioFormat(AudioFormat.Encoding.PCM_SIGNED,
                                                                                  baseFormat.getSampleRate(),
                                                                                  16,
                                                                                  baseFormat.getChannels(),
                                                                                  baseFormat.getChannels() * 2,
                                                                                  baseFormat.getSampleRate(),
                                                                                  false);
    din = AudioSystem.getAudioInputStream(decodedFormat, in);
    // Play now.
    rawplay(decodedFormat, din);
    in.close();
  } catch (Exception e)
    {
        System.out.println("exception encountered!");
    }
}

private void rawplay(AudioFormat targetFormat, AudioInputStream din) throws IOException,                                                                                                LineUnavailableException
{
  byte[] data = new byte[4096];
  SourceDataLine line = getLine(targetFormat);
  if (line != null)
  {
    // Start
    line.start();
    int nBytesRead = 0, nBytesWritten = 0;
    while (nBytesRead != -1)
    {
        nBytesRead = din.read(data, 0, data.length);
        if (nBytesRead != -1) nBytesWritten = line.write(data, 0, nBytesRead);
    }
    // Stop
    line.drain();
    line.stop();
    line.close();
    din.close();
stopBtn.setEnabled(false);
      playBtn.setEnabled(true);
  }
}

private SourceDataLine getLine(AudioFormat audioFormat) throws LineUnavailableException
{
  SourceDataLine res = null;
  DataLine.Info info = new DataLine.Info(SourceDataLine.class, audioFormat);
  res = (SourceDataLine) AudioSystem.getLine(info);
  res.open(audioFormat);
  return res;
}