Android working with Volley Library

Android volley is a networking library was introduced to make networking calls much easier, faster without writing tons of code. By default all the volley network calls works asynchronously, so we don’t have to worry about using asynctask anymore.

Volley comes with lot of features. Some of them are

1. Request queuing and prioritization
2. Effective request cache and memory management
3. Extensibility and customization of the library to our needs

4. Cancelling the requests

1. Downloading & making volley.jar

We will start with installing tools required to clone and build volley project. For this we need git (to clone the project) and ant (to build) tools.

1.1 Installing Git
Git software is used to clone git projects into your local workspace. Download & install git, once installed run git command in terminal just to make sure that it is accessible via command line. If you are getting git command not found error, add the git installation directory to environmental variables.

1.2 Installing apache ant
Apache ant is a command-line tool used to build the source code. Download ant from https://ant.apache.org/bindownload.cgi and add the bin path to environmental variables. You should able to execute ant command too in terminal.

1.3 Cloning volley library
Open command prompt, navigate to a location where you want to clone volley and execute following command. This will download a copy of volley library into your local drive.

git clone https://android.googlesource.com/platform/frameworks/volley

1.4 Making volley.jar
You can use the volley as a library project to your main project or you can simply generate volley.jar and paste it in project libs folder. To generate volley.jar, move into volley dir (cd volley) and execute below commands.

android update project -p . ant jar

You can find generated volley.jar in volley bin folder.

2. Adding volley.jar to your project

In Eclipse create a new project by navigating to File ⇒ New ⇒ Android Application Project and fill required details. Once the project is created paste the volley.jar in libs folder.

3. Creating Volley Singleton class

The best way to maintain volley core objects and request queue is, making them global by creating a singleton class which extends Application object. In your project create a class nameAppController.java and extend the class from Application and add the following code.

AppController.javapackage info.androidhive.volleyexamples.app; import info.androidhive.volleyexamples.volley.utils.LruBitmapCache;import android.app.Application;import android.text.TextUtils; import com.android.volley.Request;import com.android.volley.RequestQueue;import com.android.volley.toolbox.ImageLoader;import com.android.volley.toolbox.Volley; public class AppController extends Application {     public static final String TAG = AppController.class            .getSimpleName();     private RequestQueue mRequestQueue;    private ImageLoader mImageLoader;     private static AppController mInstance;     @Override    public void onCreate() {        super.onCreate();        mInstance = this;    }     public static synchronized AppController getInstance() {        return mInstance;    }     public RequestQueue getRequestQueue() {        if (mRequestQueue == null) {            mRequestQueue = Volley.newRequestQueue(getApplicationContext());        }         return mRequestQueue;    }     public ImageLoader getImageLoader() {        getRequestQueue();        if (mImageLoader == null) {            mImageLoader = new ImageLoader(this.mRequestQueue,                    new LruBitmapCache());        }        return this.mImageLoader;    }     public <T> void addToRequestQueue(Request<T> req, String tag) {        // set the default tag if tag is empty        req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);        getRequestQueue().add(req);    }     public <T> void addToRequestQueue(Request<T> req) {        req.setTag(TAG);        getRequestQueue().add(req);    }     public void cancelPendingRequests(Object tag) {        if (mRequestQueue != null) {            mRequestQueue.cancelAll(tag);        }    }}

Create another class named LruBitmapCache.java and paste the below code. This class is required to handle image cache.

LruBitmapCache.javapackage info.androidhive.volleyexamples.volley.utils; import com.android.volley.toolbox.ImageLoader.ImageCache; import android.graphics.Bitmap;import android.support.v4.util.LruCache; public class LruBitmapCache extends LruCache<String, Bitmap> implements        ImageCache {    public static int getDefaultLruCacheSize() {        final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);        final int cacheSize = maxMemory / 8;         return cacheSize;    }     public LruBitmapCache() {        this(getDefaultLruCacheSize());    }     public LruBitmapCache(int sizeInKiloBytes) {        super(sizeInKiloBytes);    }     @Override    protected int sizeOf(String key, Bitmap value) {        return value.getRowBytes() * value.getHeight() / 1024;    }     @Override    public Bitmap getBitmap(String url) {        return get(url);    }     @Override    public void putBitmap(String url, Bitmap bitmap) {        put(url, bitmap);    }}

Open AndroidManifest.xml and add this singleton class in <application> tag using android:nameproperty to execute this class automatically whenever app launches. Also add INTERNET permission as we are going to make network calls.

AndroidManifest.xml<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="info.androidhive.volleyexamples"    android:versionCode="1"    android:versionName="1.0" >     <uses-sdk        android:minSdkVersion="8"        android:targetSdkVersion="19" />     <uses-permission android:name="android.permission.INTERNET" />     <application        android:name="info.androidhive.volleyexamples.app.AppController"        android:allowBackup="true"        android:icon="@drawable/ic_launcher"        android:label="@string/app_name"        android:theme="@style/AppTheme" >        <!-- all activities and other stuff -->    </application> </manifest>

4. Making JSON request

Volley provides an easy to make json requests. If you are expecting json object in the response, you should use JsonObjectRequest class or if the response is json array, JsonArrayRequest class should be used.

4.1 Making json object request
Following code will make a json object request where the json response will start with object notation ‘{‘

// Tag used to cancel the requestString tag_json_obj = "json_obj_req"; String url = "http://api.androidhive.info/volley/person_object.json";         ProgressDialog pDialog = new ProgressDialog(this);pDialog.setMessage("Loading...");pDialog.show();              JsonObjectRequest jsonObjReq = new JsonObjectRequest(Method.GET,    url, null,    new Response.Listener<JSONObject>() {         @Override         void onResponse(JSONObject response) {              Log.d(TAG, response.toString());              pDialog.hide();         }    }, new Response.ErrorListener() {          @Override         public void onErrorResponse(VolleyError error) {             VolleyLog.d(TAG, "Error: " + error.getMessage());             // hide the progress dialog             pDialog.hide();         }    }); // Adding request to request queueAppController.getInstance().addToRequestQueue(jsonObjReq, tag_json_obj);

4.2 Making json array request
Following will make json array request where the json response starts with array notation ‘[‘

// Tag used to cancel the requestString tag_json_arry = "json_array_req"; String url = "http://api.androidhive.info/volley/person_array.json";         ProgressDialog pDialog = new ProgressDialog(this);pDialog.setMessage("Loading...");pDialog.show();              JsonArrayRequest req = new JsonArrayRequest(url,   new Response.Listener<JSONArray>() {       @Override       public void onResponse(JSONArray response) {             Log.d(TAG, response.toString());                     pDialog.hide();                    }   }, new Response.ErrorListener() {      @Override      public void onErrorResponse(VolleyError error) {           VolleyLog.d(TAG, "Error: " + error.getMessage());           pDialog.hide();      }   }); // Adding request to request queueAppController.getInstance().addToRequestQueue(req, tag_json_arry);

5. Making String request

StringRequest class will be used to fetch any kind of string data. The response can be json, xml, html or plain text.

// Tag used to cancel the requestString  tag_string_req = "string_req"; String url = "http://api.androidhive.info/volley/string_response.html";         ProgressDialog pDialog = new ProgressDialog(this);pDialog.setMessage("Loading...");pDialog.show();              StringRequest strReq = new StringRequest(Method.GET,                url, new Response.Listener<String>() {                     @Override                    public void onResponse(String response) {                        Log.d(TAG, response.toString());                        pDialog.hide();                     }                }, new Response.ErrorListener() {                     @Override                    public void onErrorResponse(VolleyError error) {                        VolleyLog.d(TAG, "Error: " + error.getMessage());                        pDialog.hide();                    }                }); // Adding request to request queueAppController.getInstance().addToRequestQueue(strReq, tag_string_req);

6. Adding post parameters

It is obvious that sometimes we need to submit request parameters while hitting the url. To do that we have to override getParams() method which should return list of parameters to be send in a key value format.

If you observe below example, I am submitting name, email and password as request parameters.

// Tag used to cancel the requestString tag_json_obj = "json_obj_req"; String url = "http://api.androidhive.info/volley/person_object.json";         ProgressDialog pDialog = new ProgressDialog(this);pDialog.setMessage("Loading...");pDialog.show();                      JsonObjectRequest jsonObjReq = new JsonObjectRequest(Method.POST,                url, null,                new Response.Listener<JSONObject>() {                     @Override                    public void onResponse(JSONObject response) {                        Log.d(TAG, response.toString());                        pDialog.hide();                    }                }, new Response.ErrorListener() {                     @Override                    public void onErrorResponse(VolleyError error) {                        VolleyLog.d(TAG, "Error: " + error.getMessage());                        pDialog.hide();                    }                }) {             @Override            protected Map<String, String> getParams() {                Map<String, String> params = new HashMap<String, String>();                params.put("name", "Androidhive");                params.put("email", "[e-mail]");                params.put("password", "password123");                 return params;            }         }; // Adding request to request queueAppController.getInstance().addToRequestQueue(jsonObjReq, tag_json_obj);

7. Adding request headers

Just like adding request parameters, to send request headers, we have to override getHeaders(). In below example I am sending Content-Type and apiKey in request headers.

// Tag used to cancel the requestString tag_json_obj = "json_obj_req"; String url = "http://api.androidhive.info/volley/person_object.json";         ProgressDialog pDialog = new ProgressDialog(this);pDialog.setMessage("Loading...");pDialog.show();                      JsonObjectRequest jsonObjReq = new JsonObjectRequest(Method.POST,                url, null,                new Response.Listener<JSONObject>() {                     @Override                    public void onResponse(JSONObject response) {                        Log.d(TAG, response.toString());                        pDialog.hide();                    }                }, new Response.ErrorListener() {                     @Override                    public void onErrorResponse(VolleyError error) {                        VolleyLog.d(TAG, "Error: " + error.getMessage());                        pDialog.hide();                    }                }) {             /**             * Passing some request headers             * */            @Override            public Map<String, String> getHeaders() throws AuthFailureError {                HashMap<String, String> headers = new HashMap<String, String>();                headers.put("Content-Type", "application/json");                headers.put("apiKey", "xxxxxxxxxxxxxxx");                return headers;            }         }; // Adding request to request queueAppController.getInstance().addToRequestQueue(jsonObjReq, tag_json_obj);

8. Making Image request

Volley introduced custom image view element called NetworkImageView to display the images from an URL. Previously downloading images and maintaining caches is a tough job. Now using volley this can be done with very few lines of code.

8.1 Loading image in NetworkImageView
Following will load an image from an URL into NetworkImageView.

ImageLoader imageLoader = AppController.getInstance().getImageLoader(); // If you are using NetworkImageViewimgNetWorkView.setImageUrl(Const.URL_IMAGE, imageLoader);

8.2 Loading image in ImageView
If you want to load image into ImageView instead of NetworkImageView, you can do that too as mentioned below. Here we will have success and error callbacks, you have to take appropriate action depending on the need. Below in onResponse() method using response.getBitmap() I am loading bitmap into an ImageView.

ImageLoader imageLoader = AppController.getInstance().getImageLoader(); // If you are using normal ImageViewimageLoader.get(Const.URL_IMAGE, new ImageListener() {     @Override    public void onErrorResponse(VolleyError error) {        Log.e(TAG, "Image Load Error: " + error.getMessage());    }     @Override    public void onResponse(ImageContainer response, boolean arg1) {        if (response.getBitmap() != null) {            // load image into imageview            imageView.setImageBitmap(response.getBitmap());        }    }});

8.3 Defining placeholder image and error image
Here is another way of displaying image into ImageView with the option of placeholder for loader and error. The loader placeholder will be displayed until the image gets downloaded. If the image fails to download, the error placeholder will be displayed.

// Loading image with placeholder and error imageimageLoader.get(Const.URL_IMAGE, ImageLoader.getImageListener(                imageView, R.drawable.ico_loading, R.drawable.ico_error));

9. Handling the volley Cache

Volley comes with powerful cache mechanism to maintain request cache. This saves lot of internet bandwidth and reduces user waiting time. Following are few example of using volley cache methods.

9.1 Loading request from cache
Like below you can check for a cached response of an URL before making a network call.

Cache cache = AppController.getInstance().getRequestQueue().getCache();Entry entry = cache.get(url);if(entry != null){    try {        String data = new String(entry.data, "UTF-8");        // handle data, like converting it to xml, json, bitmap etc.,    } catch (UnsupportedEncodingException e) {              e.printStackTrace();        }    }}else{    // Cached response doesn't exists. Make network call here}

9.2 Invalidate cache
Invalidate means we are invalidating the cached data instead of deleting it. Volley will still uses the cached object until the new data received from server. Once it receives the response from the server it will override the older cached response.

AppController.getInstance().getRequestQueue().getCache().invalidate(url, true);

9.3 Turning off cache
If you want disable the cache for a particular url, you can use setShouldCache() method as below.

// String requestStringRequest stringReq = new StringRequest(....); // disable cachestringReq.setShouldCache(false);

9.4 Deleting cache for particular URL
Use remove() to delete cache of an URL.

AppController.getInstance().getRequestQueue().getCache().remove(url);

9.5 Deleting all the cache
Followoing will delete the cache for all the URLs.

AppController.getInstance().getRequestQueue().getCache().clear(url);

10. Cancelling requests

If you notice addToRequestQueue(request, tag) method, it accepts two parameters. One is request object and other is request tag. This tag will be used to identify the request while cancelling it. If the tag is same for multiple requests, all the requests will be cancelled. cancellAll() method is used to cancel any request.


10.1 Cancel single request
Following will cancel all the request with the tag named “feed_request”

String tag_json_arry = "json_req";ApplicationController.getInstance().getRequestQueue().cancelAll("feed_request");

10.2 Cancel all requests
If you don’t pass any tag to cancelAll() method, it will cancel the request in request queue.

ApplicationController.getInstance().getRequestQueue().cancelAll();

11. Request prioritization

If you are making multiple request at the same time, you can prioritize the requests those you want be executed first. The priory can be Normal, Low, Immediate and High.

private Priority priority = Priority.HIGH; StringRequest strReq = new StringRequest(Method.GET,                Const.URL_STRING_REQ, new Response.Listener<String>() {                     @Override                    public void onResponse(String response) {                        Log.d(TAG, response.toString());                        msgResponse.setText(response.toString());                        hideProgressDialog();                     }                }, new Response.ErrorListener() {                     @Override                    public void onErrorResponse(VolleyError error) {                        VolleyLog.d(TAG, "Error: " + error.getMessage());                        hideProgressDialog();                    }                }) {            @Override            public Priority getPriority() {                return priority;            }         };

Missing! Making XML request

As of now volley doesn’t provided any native classes to make XML requests, but this can be achieved by building a custom xml wrapper class by utilizing volley’s customization capabilities. The part of writing xml parser using volley will be covered in upcoming tutorial.

I have given a sample project covering the scenarios explained in this tutorial. Download it and let’s discuss the queries if you have any in the comments section