JsonRequest的用法：

1.發出http請求，需要傳入四個參數(url,jsonRequest,successResponse,errorResponse)。

JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(url, null,  
        new Response.Listener<JSONObject>() {  
            @Override  
            public void onResponse(JSONObject response) {  
                Log.d("TAG", response.toString());  
            }  
        }, new Response.ErrorListener() {  
            @Override  
            public void onErrorResponse(VolleyError error) {  
                Log.e("TAG", error.getMessage(), error);  
            }  
        });

2.加入RequestQueue

mQueue.add(jsonObjectRequest);