Android中的多点方向谷歌地图

Question

如何指导多点视图Google方向API.I只能在两点之间得到 用过：

 public String request(LatLng start, LatLng end, String mode) {
    String url = "http://maps.googleapis.com/maps/api/directions/xml?origin=" + start.latitude + "," + start.longitude + "&destination=" + end.latitude + "," + end.longitude + "&sensor=false&units=metric&mode=" + mode;
    if(this.isLogging) {
        Log.i("GoogleDirection", "URL : " + url);
    }

    (new GoogleDirection.RequestTask((GoogleDirection.RequestTask)null)).execute(new String[]{url});
    return url;
}

如何在多点之间获取？帮助我。谢谢！