我想在Firebase中检索部分数据。我如何实现这一目标？

Question

片段代码

    View rootView = inflater.inflate(R.layout.fragment_contacts, container, false);

    usersList = (ListView)rootView.findViewById(R.id.usersList);
    noUsersText = (TextView)rootView.findViewById(R.id.noUsersText);

    mProgressDialogue = new ProgressDialog(getActivity());
    mProgressDialogue.setMessage("Loading...");
    mProgressDialogue.show();

    String url = "https://messageplus-cd647.firebaseio.com/.json";

    StringRequest request = new StringRequest(Request.Method.GET, url, new Response.Listener<String>(){
        @Override
        public void onResponse(String s) {
            doOnSuccess(s);
        }
    },new Response.ErrorListener(){
        @Override
        public void onErrorResponse(VolleyError volleyError) {
            System.out.println("" + volleyError);
        }
    });

    RequestQueue rQueue = Volley.newRequestQueue(getActivity());
    rQueue.add(request);

    usersList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            UserDetails.chatWith = al.get(position);
            Intent intent = new Intent(getActivity(), Chat.class);
            startActivity(intent);
        }
    });
    return rootView;

doOnSuccess 方法

public void doOnSuccess(String s){
    try {
        JSONObject obj = new JSONObject(s);

        Iterator i = obj.keys();
        String key = "";

        while(i.hasNext()){
            key = i.next().toString();

            if(!key.equals(UserDetails.phonenumber)) {
                al.add(key);
            }

            totalUsers++;
        }

    } catch (JSONException e) {
        e.printStackTrace();
    }

    if(totalUsers <=1){
        noUsersText.setVisibility(View.VISIBLE);
        usersList.setVisibility(View.GONE);
    }
    else{
        noUsersText.setVisibility(View.GONE);
        usersList.setVisibility(View.VISIBLE);
        usersList.setAdapter(new ArrayAdapter<String>(getActivity().getApplicationContext(),
                android.R.layout.simple_list_item_1 , al));
    }

    mProgressDialogue.dismiss();
}

问题是，在上面提到的URL中，存在的数据是用户的唯一ID。 Inside Unique id中有4个字段 - 名称，编号，电子邮件，性别。我想只检索用户的名字我如何实现这一目标？提前致谢