public static void lockOrientation(Activity a) {
    if (a.getResources().getConfiguration().orientation == Configuration.ORIENTATION_PORTRAIT) {
        a.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
    } else {
        a.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
    }
}

public static void unlockOrientation(Activity a) {
    a.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_UNSPECIFIED);
}