Saturday, January 25, 2014

Grunt - Create your custom local Grunt plugin

This post describes how you can write your own Grunt Plugin in Javascript and install it locally,
in order to use it on your own (Grunt) project build file.

If you don't know what Grunt is then to explain it on one leg -
"Grunt is a pluggable (JavaScript) task runner", which can be used to build JavaScript projects.

Such typical build of a Javascript project may contain a Linting task, minification task, and so on...

So, you can read more about Grunt if you want to get a better understanding.

And now, to the recipe!
1 NPM installed on your machine
1 GIT installed on your machine
1 Skill writing a tiny bit of Javascript
A zest of patience

1. First thing would be to install a Grunt plugin that is used for templates scaffolding.
In order to do that, you need to run the following in your shell:
$ npm install -g grunt-init
2. Clone a GIT repository which is going to be used as your template for creating your glorious
Grunt Plugin. (
So, run the following in your shell:
$ git clone ~/.grunt-init/gruntplugin
3. Create an empty directory where you want to place your Plugin like "my-custom-plugin", and cd into it.
$ mkdir my-custom-plugin
$ cd my-custom-plugin
Then run the following in your shell:
$ grunt-init gruntplugin
4. You should now be prompted with a serie of questions in the shell, in order to create your plugin.
You should be seeing something like this:

Please answer the following:

[?] Project name (grunt-my-custom-plugin)

[?] Description (The best Grunt plugin ever.) the best custom plugin ever!

[?] Version (0.1.0)

[?] Project git repository (ssh://<Your GIT remote Repository URL>)

[?] Project homepage (none)

[?] Project issues tracker (none)

[?] Licenses (MIT)

[?] Author name (nirgit) Nir M

[?] Author email (

[?] Author url (none)

[?] What versions of grunt does it require? (~0.4.2)

[?] What versions of node does it run on? (>= 0.8.0)

[?] Do you need to make any changes to the above before continuing? (y/N) N

Writing .gitignore...OK

Writing .jshintrc...OK

Writing Gruntfile.js...OK


Writing tasks/my_custom_plugin.js...OK

Writing test/expected/custom_options...OK

Writing test/expected/default_options...OK

Writing test/fixtures/123...OK

Writing test/fixtures/testing...OK

Writing test/my_custom_plugin_test.js...OK


Writing package.json...OK

Initialized from template "gruntplugin".

You should now install project dependencies with npm install. After that, you

may execute project tasks with grunt. For more information about installing

and configuring Grunt, please see the Getting Started guide:

Done, without errors.

5. Now you should have your directory containing a Grunt Plugin template.
Open the file you have inside the "tasks" directory in order to edit it.

6. The file should look as follows:

7. Just in order to get started, lets strip the file and change it to contain the following:
 * grunt-my-custom-plugin
 * Copyright (c) 2014 Nir M
 * Licensed under the MIT license.

'use strict';

module.exports = function(grunt) {

 grunt.file.defaultEncoding = 'utf8';

 // Please see the Grunt documentation for more information regarding task
 // creation:

 grunt.registerTask('my_custom_plugin', function() {
  grunt.log.writeln('Hello my great Grunt Plugin!') ;

The my_custom_plugin shown in bold above, is the name of your task in the Grunt build, that
you'll execute at the end.

Lets change the Gruntfile.js in the root directory of the Plugin so tests won't execute when
we will run "grunt" on the plugin's source. Otherwise the build would fail.
So now the Gruntfile.js last line should look like:
grunt.registerTask('default', ['jshint']);

8. Go back to the root directory of your Grunt Plugin and run the following:
$ npm install
$ grunt
Running "jshint:all" (jshint) task >> 3 files lint free. Done, without errors.
9. Almost done.
Now go to your own project where you want to use your plugin and add the following line to the
Gruntfile.js of your project:
This will load your Grunt plugin task to your Grunt's project.

10. Next step would be to install the plugin locally in the node modules of your Proect.
You should now run in the root directory of your Project (where you want to use your plugin) the following:
$ npm install /<PATH_TO_YOUR_PLUGIN>/my-custom-plugin
11. You should now be able to execute:
$ grunt my_custom_plugin
And see:
Running "my_custom_plugin" task

Hello my great Grunt Plugin!

Done, without errors.

That's all folks.
Hope this was helpful to get you started with Grunt Plugins.
Don't forget to publish it (npm publish) afterwards to the rest of the Node community if you think it may be helpful to others as well.

Check out the official guide for creating Grunt plugins at:

Good luck!

Sunday, June 16, 2013

Lottery for winning a copy of the "Android NDK Cookbook" is now opened

In continuation to last week's post for winning a free copy of the eBook "Android NDK Cookbook",
the lottery starts today!

3 Lucky people will be given a free copy of the "Android NDK Cookbook" sponsored by "Packt Publishing".

Description of the book

 Android Native Development Kit Cookbook will help you understand the development, building, and debugging of your native Android applications. You will discover and learn JNI programming and essential NDK APIs such as OpenGL ES, and the native application API. You will then explore the process of porting existing libraries and software to NDK. By the end of this book you will be able to build your own apps in NDK apps. 

Check it out on Packt Publishing:

How to participate?

Simply send an email by clicking here or by sending it to 
containing a subject line "Android NDK Cookbook lottery".


The contest will close on 30th June 2013. Winners will be contacted by email, so be sure to use 
your real email address! 

Good luck !

Saturday, June 8, 2013

Win a free eBook copy of "Android NDK Cookbook"

Are you an Android developer or interested in Android development?
This might interest you!

On the 16th of June 2013 I will conduct a lottery on the blog, to win a free eBook copy of "Android NDK Cookbook".

The lottery will last for 2 weeks (until June 30th) where you will be able to participate to win a free copy of the book.

Description of the book:

"Android Native Development Kit Cookbook" will help you understand the development, building, and debugging of your native Android applications. You will discover and learn JNI programming and essential NDK APIs such as OpenGL ES, and the native application API. You will then explore the process of porting existing libraries and software to NDK. By the end of this book you will be able to build your own apps in NDK apps. 

Further details of the book can be found here:

Stay tuned for the 16th of June!

* The copy of the book is sponsored thanks to "Packt Publishing".

Sunday, May 26, 2013

Javascript Closure Functions Memory Model - How does it work?

Hey everyone,
For those of you who are writing code in Javascript or wish to do so, it is essential to understand
the concept of closures, and how they work.

I must say that when I started looking into it, it was somewhat difficult to find proper material
on the web, to get a good grasp of how things work. So this post's idea is to try and shed some
light on this matter. I don't guarantee that this will make you understand everything, but do hope
it will help in some way.

*Note: I could have some mistakes in this post of course, and would be very happy if you send me
any corrections or comment as this is suppose to help people, and show the power of Javascript closures. 
Everything that's written in this post is according to my understanding of how things work.
So regard this writing with care. I tried to do the best I could when I wrote this post.

The post topics will contain 2 parts:
1. What is a Closure?
2. How does the memory model look like.

1. What is a Closure?

"... is a function or reference to a function together with a referencing environment—a table storing a reference to each of the non-local variables (also called free variables) of that function. A closure— unlike a plain function pointer—allows a function to access those non-local variables even when invoked outside of its immediate lexical scope." - From Wikipedia.

A simple example to such Closure is a counter.
Consider the following script for example:

function createCounter() {
       var counter = 0 ;
       return function() {
              counter++ ;
              return counter ;
var counter = createCounter() ;
counter() ;
// returns 1
counter() ; // returns 2
var counter2 = createCounter() ;
counter2() ; // returns 1
counter() ; // returns 3

How does this work?
The createCounter function being executed creates a new Execution Scope, which contains references to a variable named counter and returns an anonymous function.

So how does that function know about counter when it's executed?
In Javascript any function, has some kind of property called a "Scope Chain", which defines the scopes the function is bounded to. When we define a function in Javascript, the "definition scope" is such scope that is stored in the function's "Scope chain". So when we define and return the anonymous function in createCounter that anonymous function is binded to a scope where it was defined.
Thus, when the function is being executed by calling "counter()" a new "execution scope" is being created and added to the function's scope chain. So when the function needs to look up counter it looks up it's "scope-chain", and finds it eventually on the "definition scope" of the function.

Another thing to remember is that every time you run a function you run it inside a "context".

What is a context?
A context is the object the function is executed on. It is recognized with the this keyword.
It is defined when we write the following code in Javascript for example:

// context here equals to obj1 (this === obj1)
obj1.sayHello() ;

// context here equals to the global object which in case of a browser, is *window (this === window)
sayHello() ;

* It might be equal to undefined (this === undefined) in case we're running in 'strict mode'.

You can check more about it at MDN - Function Context.

2. How does the memory model look like?

I think it's important to understand how the memory model looks like, graphically, to get a better
notion of how things work. Even though you could handle without it, I find illustrations very
helpful understanding how something works.

Simple example

When you define a regular function, like:
function foo(number) {
   [ function_body ]

We get something of the following in memory:

If we execute foo(3), we will get something of the following in memory:

So when foo(3) is executed, a new "Activation object" is created.
Passing to it the function's parameters and arguments array, and adding it to the scope chain of foo(3).
So the next time foo will be looking up for the "num" parameter, it will be looking it up the
scope chain starting from the closest(last) scope that is relevant to the execution, which in this
case is of course the "Activation". If it won't find num there, it will continue to the next scope in the
chain, until it finds it.

Closure example

Lets take the Closure example we referred to earlier - the counter function and see how it 
would look like in memory.

Quick reminder, our counter function looks like this:

function createCounter() {
       var counter = 0 ;
       return function() {
              counter++ ;
              return counter ;

This maps to a memory model which looks (somewhat) like this:

counter javascript closure
You might wonder why the Closure's scope chain also refers to the Global Object.
The reason is that when we create a closure, it copies the scope chain of the execution context scope chain which in this case belongs to createCounter().
What makes the Closure a closure is the interesting side affect in Javascript, that instead of the Activation Object being destroyed after createCounter execution, it remains alive, because there is a reference to it, from another function - the closure.

Now, lets create such counter by executing the following:

var myCounter = createCounter();  [1]
myCounter() ;                     [2]

So on line [1] we create myCounter which is a reference to the closure on the above illustration.
When we execute line [2], we get 1 as an answer, and the second time we will get 2.
How it looks in the memory is shown in the next illustration:

When we execute myCounter which is our closure in this case, we are incrementing the counter variable, but in order to do so, the variable needs to be reached somehow.
This is where the "scope chain" takes its place. The first "environment" where the variable is going to be looked up is at the top of the scope chain, in our case - the "Activation Object" of myCounter.
Since the variable is not an inner variable, nor a parameter, the look-up for the variable continues, and moves on to the next scope in the chain which is the "Activation Object" of createCounter ! There it is found, read and assigned. (As counter++ is actually counter = counter + 1 ).

Note that every time you call createCounter a new Activation Object is created with a new counter variable which equals to 0. This is how you can create as many separate counters as you like, without them affecting each other.

I hope this helped you in some way to understand the memory model of functions and closures a little better. Any comments / suggestions and complaints are most welcome.
Enjoy "closuring".

Friday, March 8, 2013

GWT Chrome extension with JSONP Server communication

I thought this post would be a good idea for people who want to know how to make an 'end-to-end'
GWT Chrome extensions, with a connection to a server of their own.

While this demonstrates specifically how to enable to communication from a Chrome extension, there is
no difference in code if you wish to deploy your client code else where (not on Chrome).
Many web applications choose to deploy their Server code & Client code on the same application server, like JBoss or Tomcat.

As you know in GWT there are several ways to communicate with a server.
One of them is RPC for instance, which gives you the ability to invoke methods on a Java interface,
not having to deal with anything but Java code. Which is cool, as it makes a very smooth transition from
the client side code to the server side code.

However, when we want to implement this in a Chrome extension things get a bit trickier.
The reason is that you'd have to separate your server module from your Chrome extension module
(as we can't deploy Server side classes to Chrome - it runs only JavaScript),
and would need a shared model between the two in order to communicate.
It's not hard to do at all, it's only a longer example to make.
(In Eclipse, if you create a new "Web Application Project" using Google's plugin, you will have the client & server code in the same project, with a "shared" directory which serves a model bridge between the two).

Another option that exists, is using JSONP communication to the server.
In our case - this makes it a lot simpler.
We will expose some REST API on a Server we'll implement, for getting images, and send a JSONP request from the QuickPik extension to retrieve those images. Obviously, it can be anything else you want it to be in your application.


The Server

In order to create a REST service and expose it, we will use the Jersey library which is an implementation for
building RESTful web services. It's very simple.

The following QuickpikService class, is our REST service:

package quickpik.server.web;

import java.util.Date;


import org.codehaus.jettison.json.JSONException;
import org.codehaus.jettison.json.JSONObject;

import com.sun.jersey.api.json.JSONWithPadding;

public class QuickPikService {

private final static int BUFFER_SIZE_IN_BYTES = 1024;
private final static String FLICKR_API = "" ;

@Produces({ "application/x-javascript", MediaType.APPLICATION_JSON})
public JSONWithPadding getPhotos(@QueryParam("searchExp") String searchExp,
@QueryParam("callback") String callback) {
// "log" the call
System.out.println("[" + new Date() + "] searching for: " + searchExp) ;
URL flickrUrl = getSearchURL(searchExp) ;
JSONObject data = tryToGetSearchResult(flickrUrl);
return new JSONWithPadding(data, callback);

private URL getSearchURL(String searchExp) {
String composedURL = FLICKR_API + searchExp;
try {
return new URL(composedURL);
} catch (MalformedURLException e) {
throw new RuntimeException("URL composition failed. Please check your URL: " + composedURL, e) ;

private JSONObject tryToGetSearchResult(URL flickrUrl) {
try {
return getSearchResult(flickrUrl) ;
} catch (IOException | JSONException e) {
throw new RuntimeException("Failed searching.", e) ;

private JSONObject getSearchResult(URL flickrUrl) throws IOException, JSONException {
InputStream is = flickrUrl.openStream() ;
String result = readDataFromStream(is);
// Flickr specific string prefix for the JSON feed.
if(result.indexOf("jsonFlickrFeed(") >= 0) {
result = result.substring("jsonFlickrFeed(".length(), result.length()-1) ;
return new JSONObject(result) ;
} else {
return new JSONObject("{}") ;

private String readDataFromStream(InputStream is) throws IOException {
StringBuilder data = new StringBuilder() ;
byte[] buffer = new byte[BUFFER_SIZE_IN_BYTES] ;
int bytesRead = ;
while(bytesRead != -1) {
data.append(new String(buffer, 0, bytesRead)) ;
bytesRead = ;
is.close() ;
return data.toString() ;

That's it. This our REST service, and we are exposing our API by using the @Path annotations
on the class and on the public method getPhotos. There are also other annotations such as the
@GET annotation and the @Produces annotation which state that the method is invoked on
an HTTP GET, and returns (@Produces annotation) a JSON (with Padding eventually = JSONP) object.

As you can see, in the class, we are using a Flickr API to get our images data from.

Now all that's left in order to make this service work, is to define the Jersey servlet in the web.xml file,
which is done this way:


    <servlet-name>Jersey REST Service</servlet-name>

    <servlet-name>Jersey REST Service</servlet-name>


After doing that, we're able to refer to our REST service by using a URL in the browser:

In order to verify this worked indeed and to get a better understanding of how the strucutre of our JSON result looks like, before even writing code to the GWT Chrome extension client,
i did a small test using jQuery, to see whether this worked. - You can find it in the GitHub repository.
What I did in a nutshell, was to call the REST API:
$.getJSON('http://localhost:8080/qpserver/rest/quickpik/searchPhotos?searchExp=hello&callback=?', jsonCB);

So I executed an AJAX call to search for "hello", and passed a callback - jsonCB to process the result.
jsonCB looks like this:

function jsonCB(result) {
if (result !== null && result) {
if (result.items.length === 0) {
$($("#serverResponses")[0]).append("No results.")
} else {
for (item in result.items) {
var url = result.items[item].media.m;
var imgItem = document.createElement('img');
imgItem.src = url;
$($("#serverResponses")[0]).append("Server response: ")

Note the highlighted text! - This is how we get the URL information of the photo items being sent back to us from the server.
So now we know that inside "result" which is a JSON object, resides an array of objects, that contain each
an object called media with a field called m.
You can discover this by simply debugging the returned values from the Server in the browser.

So now, we can finally add some code to our GWT Client.

Client side - GWT Chrome extension

In the previous posts of QuickPik, you might have noticed, that in order to add an additional ImageDataSource, all you need is to implement an Interface IImagesDataSource and add that ImageDataSource to the DataSource enum.
It's much easier than it sounds.
So we need to do the following:
1. Write an ImageDataSource that "talks" to our Server.
2. Edit the manifest.json file to allow communication to our server in order to comply with the
    "Content Security Policy" of Chrome's extensions.

IImageDataSource implementation - ServerDS

public class ServerDS implements IImagesDataSource {

private final static String QUICKPIK_SERVER_URL = 
"http://localhost:8080/qpserver/rest/quickpik/searchPhotos?searchExp=" ;


public void getImages(final String searchExpression, final FilterLevel filter, 
                                                 final Callback<PhotosSearchResult, Void> callback) {
String url = QUICKPIK_SERVER_URL + searchExpression ;
JsonpRequestBuilder jsonp = new JsonpRequestBuilder();
jsonp.requestObject(url, new AsyncCallback<ServerResult>() {
public void onFailure(Throwable throwable) {
// do some error handling..

public void onSuccess(ServerResult result) {
handleLoadedImagesResult(searchExpression, filter, result, callback) ;

private void handleLoadedImagesResult(String searchExpression, FilterLevel filter, ServerResult result, 
Callback<PhotosSearchResult, Void> callback) {
JsArray<ServerImageItem> imageItems = result.getItems();
LinkedList<Photo> photos = collectImages(imageItems);
callback.onSuccess(new PhotosSearchResult(searchExpression, filter, photos, 0, false)) ;

private LinkedList<Photo> collectImages(JsArray<ServerImageItem> imageItems) {
LinkedList<Photo> photos = new LinkedList<Photo>();
for (int i = 0; i < imageItems.length(); i++) {
ServerImageItem imageItem = imageItems.get(i);
Photo p = new Photo(i+"", imageItem.getImageURL(), imageItem.getImageURL()) ;
photos.add(p) ;
return photos;

I'll try to explain the code very shortly:
1. At the top of the class you can locate the URL to the server we will be using to get the images from.
2. getImages method which must be implemented is passed a searchExpression a filter and
   a callback. We will ignore the filter to make things simpler.
   GWT offers a class called JsonpRequestBuilder which allows us to invoke an asynchrounous
   call to the server, and passing a callback to deal with the result of the invocation.
3. If the call was successful, we have to handle the result somehow. We do that by calling a handle method.
4. In the handleLoadedImagesResult method, we got an object called ServerResult. 
    ServerResult is a custom object created especially for this operation. It is a wrapper to
    a JavaScriptObject, that gives access to the result.items object array. (Remember from the jQuery test?)

This is how ServerResult looks like:

public class ServerResult extends JavaScriptObject {

   protected ServerResult() {

   public final native JsArray<ServerImageItem> getItems() /*-{
     return this.items ;

The native getItems method, is a convention of GWT to write JavaScript code to the underlying JavaScriptObject that the Java object wraps. So when you invoke getItems, behind the scenes the
JavaScript code "return this.items" is executed, returning the JavaScript items Array.

I also mapped the objects in this array to a Java object in the same way I did with ServerResult.
Following the same idea, ServerImageItem looks like this:

public class ServerImageItem extends JavaScriptObject {

protected ServerImageItem() {

public final native String getImageURL() /*-{
    return ;

Here we use getImageURL method to return the (JavaScript) object's media.m property.
(This is exactly the same structure that was referred to when testing with jQuery above).

So after this long explanation, all we do in the "handle" method, is basically gathering all of our
images URLs, creating a Photo list, like expected in the callback passed to us in the getImages method
invocation and invoking the callback, passing it an expected PhotoSearchResult object containing
our Photos.

5. Now we must add our ServerDS to the DataSource enum, so it will be included as a data source
    when we run a search.
    We do that simply by adding the (bolded) line below:

public enum DataSource {

// add here your data sources
FLICKR(false, new FlickrDS()),
QUICKPIK_SERVER(true, new ServerDS())

Notice how I intentionally turned off FLICKR Data Source, setting its isEnabled flag to false.

6. Last thing that needs to be done, is to enable our Chrome extension to make calls to our server by
    editing the manifest.json file, adding the following line to it:

   // A relaxed policy definition which allows script resources to be loaded from localhost:8080 over HTTP
  "content_security_policy": "script-src 'self' http://localhost:8080; object-src 'self'"

That's all folks, all you need to do now, is build the Server (I did it with Gradle in this project), compile
your GWT client, deploy it on Chrome and watch it work.

You can access all the code on GitHub, and download it.

Code on GitHub
All of the project's code can be found on GitHub at: