Extracting data from JsonArray,Try something like this.
if (jsonStr != null) {
         try {
                    JSONObject jsonObj = new JSONObject(jsonStr);
                         // Getting JSON Array node
                        JSONArray contacts = jsonObj.getJSONArray("response");
                        // Getting JSON User Object node
                        JSONObject userObj = contacts.getJSONObject("user");
            //Getting name key from user object                    
                         String name = userObj.getString("name");
                        //Getting avatar node from user object 
                        JSONObject avatarObj= userObj.getJSONObject("avatar");
                        //Getting base key from avatar object  
                        String base= avatarObj.getString("base");
                } catch (final JSONException e) {
                    Log.e(TAG, "Json parsing error: " + e.getMessage());
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            Toast.makeText(getApplicationContext(),
                                    "Json parsing error: " + e.getMessage(),
                                    Toast.LENGTH_LONG)
                                    .show();
                        }
                    });
                }
    }