private int currVolume = 0;
/**
* 打開揚聲器
*/
private void openSpeaker() {
    try{
      AudioManager audioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
      audioManager.setMode(AudioManager.ROUTE_SPEAKER);
      currVolume = audioManager.getStreamVolume(AudioManager.STREAM_VOICE_CALL);
      if(!audioManager.isSpeakerphoneOn()) {
        //setSpeakerphoneOn() only work when audio mode set to MODE_IN_CALL.
        audioManager.setMode(AudioManager.MODE_IN_CALL);
        audioManager.setSpeakerphoneOn(true);
        audioManager.setStreamVolume(AudioManager.STREAM_VOICE_CALL,
            audioManager.getStreamMaxVolume(AudioManager.STREAM_VOICE_CALL ),
            AudioManager.STREAM_VOICE_CALL);
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
}
/**
* 關閉揚聲器
*/
public void closeSpeaker() {
    try {
      AudioManager audioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
      if(audioManager != null) {
        if(audioManager.isSpeakerphoneOn()) {
          audioManager.setSpeakerphoneOn(false);
          audioManager.setStreamVolume(AudioManager.STREAM_VOICE_CALL,currVolume,
              AudioManager.STREAM_VOICE_CALL);
        }
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
}