Service first using JAX-WS

There are two ways for developing services using JAX-WS, service first, and contract first. Service first means you would typically write the implementation first and generate the WSDL afterwards, whereas contract first you would define the WSDL first, then write the implementation afterwards. There are pros and cons for each approach, but I won’t dwell on those now.

There are 2 parts to a JAX-WS service, the Service Endpoint Interface (SEI) and the Service Implementation Bean (SIB). The SEI is an interface where you abstractly declare the methods (or operations) that your service will provide, along with the inputs and outputs. The SIB is a concrete implementation of the SEI, where you actually implement the code for the SEI. Let me show you a basic example


import javax.jws.WebMethod;
import javax.jws.WebService;
import javax.jws.soap.SOAPBinding;

@SOAPBinding(style = SOAPBinding.Style.RPC)
public interface TeamService {

    public String getTeam();


import javax.jws.WebService;

@WebService(endpointInterface = "com.jameselsey.webservices.basicimplementationfirst.service.TeamService")
public class TeamServiceImpl implements TeamService{

    public String getTeam(){
        return "Geelong Cats";

That is pretty much it, now we just need to deploy the service. Lets avoid using a servlet container for now, as it complicates this example somewhat, we can run the service by implementing the following and taking advantage of the publish method on Endpoint.

import com.jameselsey.webservices.service.sib.TeamServiceImpl;

public class Runner {

    public static void main(String[] args) {
        String address = "http://localhost:9876/footy";
        Endpoint.publish(address, new TeamServiceImpl());

        System.out.println("Server up and running on " + address);

If you then open http://localhost:9876/footy on your browser you’ll see a page listing the services and their WSDLs. The generated WSDL should look something like this.

<?xml version="1.0" encoding="UTF-8"?>
<definitions xmlns="" xmlns:soap="" xmlns:tns="" xmlns:wsam="" xmlns:wsp="" xmlns:wsp1_2="" xmlns:wsu="" xmlns:xsd="" targetNamespace="" name="TeamServiceImplService">
   <types />
   <message name="getTeam" />
   <message name="getTeamResponse">
      <part name="return" type="xsd:string" />
   <portType name="TeamService">
      <operation name="getTeam">
         <input wsam:Action="" message="tns:getTeam" />
         <output wsam:Action="" message="tns:getTeamResponse" />
   <binding name="TeamServiceImplPortBinding" type="tns:TeamService">
      <soap:binding transport="" style="rpc" />
      <operation name="getTeam">
         <soap:operation soapAction="" />
            <soap:body use="literal" namespace="" />
            <soap:body use="literal" namespace="" />
   <service name="TeamServiceImplService">
      <port name="TeamServiceImplPort" binding="tns:TeamServiceImplPortBinding">
         <soap:address location="http://localhost:9876/footy" />

The important parts in the WSDL that I should mention are:

The port section describes the operations that the service exposes, you can think of this a little bit like a Java interface, where it declares the inputs and outputs abstractly, but mentions nothing about the actual implementation. You will notice that the operations match onto the methods marked as @WebMethod. Notice that the name on the port matches the interface and not the implementation.
The binding section is where you mention implementation details for an implementation of the interface (port), such as transport, style, and usages. Transport is typically http (although smtp can be used), style matches onto the SOAPBinding annotation that we set. The default style is document however I’ve overridden this to be rpc as it makes the examples easier to follow as its less complex.
The service section maps interfaces onto implementations, or in WSDL terms, it lists the ports and their bindings. In the above example it mentions that there is an implementation of TeamServiceImplPort as described in TeamServiceImplPortBinding, available on http://localhost:9876/footy.

You can actually see this working, by creating a project from the WSDL using SOAPUI, it will generate the following request for you

<soapenv:Envelope xmlns:soapenv="" xmlns:sei="" xmlns:sib="">

As you can see the body contains a tag which is requesting the getTeam port, ultimately bound onto the getTeam Java interface method, implemented to return a pre defined string. If you execute the request, you’ll get the following response

<S:Envelope xmlns:S="">
      <ns2:getTeamResponse xmlns:ns2="">
         <return>Geelong Cats</return>

This was a quick brain dump of a simple JAX-WS service (I’m currently studying for the Oracle web services certification, trying to write my notes up). I’ve covered how to implement a SEI/SIB, how to publish a service, covered in brief the elements of the WSDL we’re interested in, and showed how the service can be invoked. Please check back soon as I’ll continue this example and post more of my study notes.

Grails based survey system, the android app

Some time back I wrote an article describing the roosearch system I developed using grails. This is the second part, the android client, please checkout the previous article otherwise this might not make much sense!

After completing the grails component, I had a RESTful API available to me, and I just needed to build an app that could consume those services.

Customer lookup and QR codes

The app needs to be simple and quick to use, one of the things I remember from a UX discussion at DroidCon UK is “Don’t annoy your users, they control your app ratings and your income!”. In order to lookup the surveys quickly, I’ve added the ability to scan QR codes. Actually I didn’t have to do a great deal as there is already an app called ZXing by Google that scans QR codes, so I just needed to make Roosearch delegate to ZXing and handle the result.

Of course, we don’t want to exclude users that don’t have ZXing, or even a camera on their device, so I’ve also provided a text field where they can enter the customer Id manually if required.

When the user clicks on the “scan barcode” button, I first check if ZXing is installed using the following

    public void scanBarCode(View v) {
        final boolean scanAvailable = isIntentAvailable(this,
        if (!scanAvailable){
            Toast.makeText(this, "You need to install the ZXing barcode app to use this feature", Toast.LENGTH_SHORT).show();

        Intent intent = new Intent("");
        intent.putExtra("SCAN_MODE", "QR_CODE_MODE");
        startActivityForResult(intent, 0);

If the user does have ZXing installed on their device, and choose to use it, we can get the result back from the bar code scan using:

public void onActivityResult(int requestCode, int resultCode, Intent intent) {
        if (requestCode == 0) {
            if (resultCode == RESULT_OK) {
                String contents = intent.getStringExtra("SCAN_RESULT");
            } else if (resultCode == RESULT_CANCELED) {
                // Handle cancel

    private void performRooLookup(String rooId) {
        if (StringUtils.isBlank(rooId)) {
            Toast.makeText(this, "Please enter a valid customer id", Toast.LENGTH_SHORT).show();

        Integer customerId;
        try {
            customerId = Integer.parseInt(rooId);
        } catch (NumberFormatException e) {
            Toast.makeText(this, "Customer id needs to be numeric", Toast.LENGTH_SHORT).show();
        new FindRooTask(this, new FindRooTaskCompleteListener()).execute(customerId);

I then have the following buried in a service call, invoked by an AsyncTask, which handles finding Customer details:

    public Customer getCustomerDetails(int customerId) {

        try {
            final String url = "{query}";

            HttpHeaders requestHeaders = new HttpHeaders();

            // Create a new RestTemplate instance
            RestTemplate restTemplate = new RestTemplate();
            restTemplate.getMessageConverters().add(new MappingJacksonHttpMessageConverter());

            // Perform the HTTP GET request
            ResponseEntity<Customer> response =, HttpMethod.GET,
                    new HttpEntity<Object>(requestHeaders), Customer.class, customerId);

            return response.getBody();
        } catch (Exception e) {
            System.out.println("Oops, got an error retrieving from server.. + e");
         return null;

A Customer looks like this:

public class Customer implements Parcelable {

    private String companyName;
    private String twitter;
    private String facebook;
    private List<SurveySummary> surveys = new ArrayList<SurveySummary>();
    //Accessors omitted

The SurveySummary just has a title and Id. The reason for just returning summaries is because a customer may have many surveys, and there is no need to obtain them all, we just obtain the title to display to the user, if selected, we’ll retrieve the survey by its id.

To recap, here are 2 screenshots that show the above; the landing screen, and then the customer display screen

Landing screen for Roosearch, where the user can enter a customer Id or scan a QR code
Landing screen for Roosearch, where the user can enter a customer Id or scan a QR code
Customer screen, display social media links, name, photo, and list of surveys that the customer has
Customer screen, display social media links, name, photo, and list of surveys that the customer has


The survey engine

This is where the magic happens. I have a single activity and single view that handles presenting the survey to the user. As the surveys can change number of questions, and number of responses, I needed a way of dynamically traversing the survey object and allowing user to move between the questions whilst retaining state of what they have selected so far.

I’ve created the following method that will redraw the layout for a given question id:

    public void drawQuestionOnScreen(int id) {
        TextView question = (TextView) findViewById(;
        question.setText(s.getQuestion(id - 1).getText());   // subtract 1 as lists are indexed from 0

        LinearLayout linLay = (LinearLayout) findViewById(;
        RadioGroup rg = new RadioGroup(this);
        for (int aIndex = 0; aIndex < s.getQuestion(id - 1).getResponses().size(); aIndex++) {
            Answer a = s.getQuestion(id - 1).getAvailableOption(aIndex);
            RadioButton button = new RadioButton(this);

        TextView status = (TextView) findViewById(;
        status.setText(format("%d of %d", id, s.getQuestionCount()));

As you can see, it will retrieve the question by Id, then iterate over the responses and generate RadioButtons. Moving to the next question is reasonably easy, firstly I work out if an option has been selected, and prevent moving on if not. After that, I mark the selected response in the survey object, and then work out if there is another question in the sequence to display, if not we can progress to the finish.

One of the questions in the given survey
One of the questions in the given survey
    public void next(View v) {
        RadioGroup rg = (RadioGroup) findViewById(1);

        int selectedRadioId = rg.getCheckedRadioButtonId();
        if(selectedRadioId == -1){
            Toast.makeText(this, "Please select a response", Toast.LENGTH_SHORT).show();

        s.getQuestion(questionIndex - 1).getResponses().get(selectedRadioId).setSelected(true);
        // work out if there is another question, then move to it
        if (s.getQuestionCount() > 1 && questionIndex < s.getQuestionCount()) {
        } else {
            // if there are no other questions, show dialog saying submit or not
            Toast.makeText(this, "Reached the end of the survey", Toast.LENGTH_SHORT).show();
            // HERE we should process the entire survey, crunch data and post off (maybe async)

            Intent i = new Intent(this, SurveyComplete.class);
            i.putExtra("com.roosearch.domain.Survey", s);

A similar approach is needed for moving back to previous questions, determine if there is a previous question to move to then redraw the screen, like so:

    public void previous(View v) {
        // work out if there is a previous question, and if so move to it
        if (s.getQuestionCount() > 1 && questionIndex > 1) {
        } else {
            //if there are no other questions, move back to home screen, finish() this and scrap any progress

Once the user completes all questions, the SurveyComplete activity is invoked.

Completing a survey

When the user has completed all questions, the survey object is passed into the SurveyComplete activity, which handles sending the responses back to the grails web application.

    protected void onResume()
        TextView tv = (TextView) findViewById(;
        tv.setText("Thank you for taking the time to complete the survey");

        Survey s = getIntent().getExtras().getParcelable("com.roosearch.domain.Survey");

        if (s != null)
            StringBuffer sb = new StringBuffer();
            sb.append("\n" + s.getTitle() + "\n");
            for (Question q : s.getQuestions())
                sb.append("\nQ: " + q.getText());
                sb.append("\nA: " + q.getSelectedAnswer() + "\n");
            tv.append("\n\n" + sb.toString());

        new SurveyUploadTask(this, new SurveyUploadTaskCompleteListener()).execute(s);

    public class SurveyUploadTaskCompleteListener implements AsyncTaskCompleteListener<Void> {
        public void onTaskComplete(Void voidz) {
            Toast.makeText(SurveyComplete.this, "Survey uploaded", Toast.LENGTH_SHORT).show();

The activity uses an AsyncTask to post the data back to the grails API controller, and displays a toast when successful.

Survey completed, results uploaded, and summary presented to user
Survey completed, results uploaded, and summary presented to user


Wrapping it up

Overall quite a simple app, I spent probably around 2 or 3 weekends putting together, most of that time was spent getting to grips with some automated testing for android. The code is admittedly a little rough around the edges, but I was aiming for an MVP (most viable product) to get working, feel free to contribute or suggest improvements!

I chose to use maven, but would use gradle if I were to pick this up again. Be sure to check out the code on github and try running it against Roosearch web, it does work!

Click here for the source code on Github

Changing the hostname on your raspberry pi

By default, the hostname on a raspberry pi installation will be “raspberrypi”, which is great if you just have the one pi.

Two raspberry pis, one with a BrickPi attached for controlling lego mindstorms
Two raspberry pis, one with a BrickPi attached for controlling lego mindstorms

If you’ve got more than one, then you’re going to get hostname conflicts when you attach both to your network. Fortunately its easy to correct this.

Plug the pi that you want to change hostname onto the network (leave the other unattached). That way when you ssh onto raspberrypi, you know which one it is.

Next, edit the hosts file.

sudo nano /etc/hosts

You’ll need to change the last line to whatever you want to name the pi, in my case I called it robopi       localhost
::1             localhost ip6-localhost ip6-loopback
fe00::0         ip6-localnet
ff00::0         ip6-mcastprefix
ff02::1         ip6-allnodes
ff02::2         ip6-allrouters       robopi

Exit that file and then change the hostname file

sudo nano /etc/hostname

Change it to the same name you put in the hosts file


Thats the configuration changes done, next we need to restart the hostname service, but executing:

sudo /etc/init.d/

Then restart the pi

sudo reboot

After that, you should be able to ping and connect to robopi:

Jamess-MacBook-Pro:pi Elsey$ ping robopi
PING robopi.home ( 56 data bytes
64 bytes from icmp_seq=0 ttl=64 time=1.802 ms
64 bytes from icmp_seq=1 ttl=64 time=4.141 ms
--- robopi.home ping statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 1.802/2.971/4.141/1.170 ms
Jamess-MacBook-Pro:pi Elsey$ ssh pi@robopi
pi@robopi's password: 
Linux robopi 3.6.11+ #456 PREEMPT Mon May 20 17:42:15 BST 2013 armv6l

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Sun Dec 29 15:59:40 2013 from unknown
-bash: /etc/profile: is a directory
pi@robopi ~ $ hostname

Thats it, you can connect the original “raspberrypi” to the network, or change the hostname of that too

Getting to grips with Grails, building a survey management system

Sometime in late 2012 I was discussing dissertation project ideas with my girlfriend, as she was coming up to her final year of a computing bachelors. The usual option chosen by many graduates would be to just build a website or an app, or do some form of market research. We decided to encompass all 3 to produce something that works, but ultimately something that could be of value. If I had the time, energy, and funds I’d pursue this as it has potential for a startup, but I don’t, so the important thing that I’ve taken away is the experience working with groovy, grails, and android.

The Idea…

There are 2 main business drivers behind this project. Firstly we wanted to provide a service whereby restaurant owners can register, create surveys, and make them accessible to staff such as printing QR codes onto the back of their menus. Secondly, we wanted to approach this from the end users point of view, whereby customers sitting in the restaurant could download an app for free off the public market places, scan the said QR code, and be presented with the survey the restaurant owner had created. They would fill it in via the app and submit, the restaurant owner then has immediate access to the results in the form of statistics and graphs.

Landing page for Roosearch
Landing page for Roosearch

The outcomes that we’re after:

  • Better visibility to restaurant owners on how their customers feel
  • Easy and seamless access to surveys for the customers
  • A scalable application which can handle increasing users as demand grows
  • A platform for advertising new products and features

There are 3 components to this solution:

  1. Grails web application
  2. Rest API (built into the grails application)
  3. Android app

Why Grails?

  • Develop in groovy, so very accessible to java developers.
  • Quick to prototype with “convention over configuration”
  • Views auto generated if using scaffolding.
  • Easily deployable into the cloud, package as a war and deploy to cloudbees

The Prototype…

If you’re starting out with grails, I’d highly recommend that you get a copy of IntelliJ ultimate edition (and a copy of Grails in action), the support for grails is fantastic and I found it far easier than using eclipse. Whilst there are some excellent tutorials on grails out there (the official documentation is also very good) I’ll hold off and just jump right into how the application works.

One of the awesome features of grails is that it follows the “convention over configuration”, which simply means that if you follow the convention implied by the framework, you don’t have to be concerned about configuration. You can’t escape configuration entirely, but boilerplate plumbing can be inferred by convention. An example of that is if you name your controllers like “SurveyController”, grails automatically knows its a controller for the survey class, based on naming conventions. A similar convention applies for views.

Domain model

Roosearch entity relationship diagram
Roosearch entity relationship diagram

Our data model is quite simple. We have a user, the user has some surveys, each survey has a number of questions, and each questions has a number of predefined responses. The domain classes are self explanatory, but it’s probably worth mentioning a few tweaks I made.

class User {
    String firstName
    String lastName
    String emailAddress
    String companyName
    String facebookPageLink
    String twitterHandle

    static hasMany = [surveys: Survey]
    static constraints = {
        facebookPageLink nullable: true
        twitterHandle nullable: true

By default, all fields are mandatory, however in the above example of the User class we can override these constraints to set them as nullable. There are various other constraints that you can set, have a look at the documentation.

class Survey {

    Integer id
    String title

    static hasMany = [questions: Question]

    static mapping = {
        questions lazy: false

    static constraints = {

    String toString(){
        return title

The relationships between the classes are defined by the “static hasMany”. This basically says that one Survey has relationships to many Questions, and this relationship is identified by “questions”.

The mapping block instructs the questions to be eagerly loaded, so once a survey is loaded into memory, so are all of its questions, opposed to just the Ids which would then be loaded lazily.

It’s also useful to override the toString method on your domain objects, particularly if you have relationships as the scaffolding will create drop down lists in your views. If you don’t override toString with something sensible, you’ll just see the object hash codes instead, which isn’t very useful to the user.


It’s the responsibility of the controllers to manipulate the underlying data model (via services for example), and respond with views to the user. You can read more about the MVC pattern here.

To get started, you could simply enable scaffolding like so.

class LoginController {

    static scaffold = true

    def index = {
        render(view: "login.gsp")

Scaffolding is an excellent feature of grails to get you started. Grails knows the structure of your domain object, therefore it is able to dynamically create controller CRUD operations, and views to manipulate your objects. That one small line of code and you can create, updated, delete, and view your objects! Fantastic eh?!

The bad news…

Whilst scaffolding is great to get you started, the moment you want to do something out of the ordinary, or customisation on views, scaffolding becomes a bit useless, and you’ll have to implement your own controllers (and possibly views). Fortunately, grails is quite flexible so you can leave scaffolding on and just override the methods that you want to customise. As with views, you’re best off getting grails to generate them for you and then customise them, to save you having to write the entire controller/view from scratch.

The methods you can override, and there general uses are:

  • index – default action, usually just redirects to list
  • list – list all of the objects, handle pagination, filtering etc
  • create – render view to create new object
  • save – handle creation of new object, validation etc.
  • edit – render view to edit an object
  • update – handle update of object
  • delete – delete an object

You can read more about the controller actions on the grails documentation.

You can see in the show() method on the SurveyController that I’ve customised it to to add some charts into the response model. You can see how I generate the chart data by looking at the source code in github. The view can then render these as javascript charts (which I’ll come onto in a moment)

    def show(Long id) {
        def surveyInstance = Survey.get(id)
        if (!surveyInstance) {
            flash.message = message(code: 'default.not.found.message', args: [message(code: 'survey.label', default: 'Survey'), id])
            redirect(action: "list")

        def charts = getCharts(surveyInstance)

        [surveyInstance: surveyInstance, charts: charts]


Being quite fond of the default views that grails generates, and not wanting to invest a great deal of time with customisation for this prototype, I chose to generate the views and then just tweak as I needed. In reality, the only customisation I needed to do was to place a “generate QR code” link, and to insert some javacript charts for displaying survey statistics.

Having assessed HighCharts, D3, and the Google visualisation API, I opted for the latter as I felt it was far simpler to use and I didn’t have any need for the advanced features that HighCharts and D3 come with, and there was a plugin for gvisualisation.

Displaying charts was straightforward, after installing the visualisation plugin, add this snippet of code to iterate over the charts that were added to the model and display a barCoreChart.

<g:each in="${charts.values()}" var="item">
                    width="${400}" height="${240}"

            <div id="chart-${item.question_id}" align="center"></div>

This would then display something like the following, you can change various elements of the charts such as the chart type, axis labels, sizes and titles, please refer to the documentation.

Charts using Google Visualisation
Charts using Google Visualisation

QR codes

QR codes make it incredibly easy to share data to android devices, my intention was to embed a user ID in a QR code, when scanned the app can request all surveys pertinent to the user ID.

Generating QR codes is easy with the qrcode plugin. I have provided a link on the users view to generate a QR code:

<span class="property-value" aria-labelledby="qr-label">
                <g:link controller="user" action="generateQrCode" id="${}">Generate QR Code</g:link>

This is bound to the generateQrCode action on the user controller, which will create a QR code from a user id and display it

    def generateQrCode(Long id){
        println "Generate QR code here..."
        String data = "$id"
        int qrSize = 500

        QRCodeRenderer qrcodeRenderer = new QRCodeRenderer()
        qrcodeRenderer.renderPng(data, qrSize, response.outputStream)

As you can see, it is as simple as providing the data to be encoded, the size (x==y), and the output stream, in this case the response. When you click the link, you should see the following:

QR code generated by the qrcode plugin
QR code generated by the qrcode plugin


The website element is designed for the restaurant owners, the end users will be using an android app to complete surveys. Whilst I could have developed a mobile responsive page, I felt that an android app would bring a better overall experience to the user.

I have created a controller, ApiController that enables users to request surveys, and post responses.

Firstly, I created the URL mappings for this new controller

	static mappings = {
        "/api/customer/$customerid"(controller: "api", action: 'getCustomer')
        "/api/survey/$surveyid"(controller: "api", action: [GET: 'getSurvey'])
        "/api/survey"(controller: "api", action: [POST: 'surveyComplete'])

            constraints {
                // apply constraints here

		"/"(controller: "home")

Requests on /api/customer/$customerid, such as /api/customer/123 are routed to the getCustomer method on the api controller. The same is true for the second mapping, however the action is a GET on getSurvey (in hindsight, the first mapping should be restricted to the GET method too). The third mapping is a POST on /api/survey which will be invoked when the user has completed a survey on their device.

    def getCustomer(){
        User u = User.get(params.customerid)

        def surveysToPresent = [:]

        u.surveys.each {
            surveysToPresent << [title: it.title, id:]
        render(contentType: 'text/json') {[
                'company_name': u.companyName,
                'twitter' : u.twitterHandle,
                'facebook' : u.facebookPageLink,
                'surveys' : [surveysToPresent]
        ]} as JSON

The getCustomer method finds the user from the customerid on the request path, retrieves the surveys and transforms them to a map containing the title and id (we don’t need the entire survey object when the user is presented with a list of surveys to select). The render statement enables us to return a json response very easily, we just return a map and grails (jackson) takes care of the json marshalling.

    def getSurvey(){
        Survey s = Survey.get(params.surveyid)

        def questionsToPresent = [:]

        questionsToPresent = s.questions.collect {
                    text: it.text,
                    responses : it.responses.collect{ resp ->
                        [id:, text: resp.text]

        render(contentType: 'text/json') {[
                'id' :,
                'title': s.title,
                'questions' : questionsToPresent
        ]} as JSON

The getSurvey method behaves in a similar manner to getCustomer, it builds a map and renders as json.

    def surveyComplete(){
        def jsonObject = request.JSON

        Survey theSurvey = Survey.findById(

        jsonObject.responses.each{ response ->
            theSurvey.questions.find { == response.question_id}.responses.find { == response.response_id}.numberOfPeopleSelected++
        } true, failOnError: true)

        render(status: 204)

The surveyComplete will retrieve a survey by id, find the responses the user has provided, and increment a count. The survey is then saved and a “204 No Content” is returned.

I’ll cover how the android app consumes these services in my next post.


As this project is just a prototype, I decided to host it on a free Cloudbees instance. The application doesn’t have any persistence layer, and all data is held in memory (which is fine for its current purpose), so when Cloudbees hibernates the instance after a period of inactivity, all user data will be lost. Deploying is simple, build the war using

grails war

Then upload the war file from the target directory to your cloud bees account, or use the command line cloud bees SDK.

View source code on Github

View live demo

(if the live demo link doesn’t work, try again in 10 minutes as the instance will be waking from hibernation)


Project Euler, problem 4, palindromes

Problem 4:

A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.

Find the largest palindrome made from the product of two 3-digit numbers.

Firstly I decided to try and solve the problem using two 2-digit numbers so I can understand how the creator of this problem got to 9009.

In about 15 minutes I was able to come up with this brute force hack:

public class Problem4 {

    public static void main(String[] args) {

    private static void solve() {
        int highestPalindrome = 0;

        for (int left = 99; left &gt; 2; left--) {
            for (int right = 99; right &gt; 2; right--) {
                int candidate = left * right;
                if (isPalindrome(candidate)) {
                    System.out.println(format(&quot;Palindrome found! Using %d * %d = %d &quot;, left, right, candidate));
                    if (candidate &gt; highestPalindrome) {
                        highestPalindrome = candidate;
        System.out.println(&quot;Highest palindrome is &quot; + highestPalindrome);

    private static boolean isPalindrome(int palindrome) {
        String palindromeString = &quot;&quot; + palindrome;
        String reversed = new StringBuilder(palindromeString).reverse().toString();
        return palindromeString.equals(reversed);

Which gives the output of

Highest palindrome is 9009

Excellent, so we’re on the right track. The next thing I did was alter the loop statements to start at 999, which then prints the following

Highest palindrome is 906609

Which is the correct answer!

Any suggestions on improvements? Please comment!

Project Euler, problem 3, largest prime factor

Problem 3 :

The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 600851475143 ?

To solve this, I needed to understand the process of prime factorisation (surprisingly, it is something which I was never taught at school/uni).

What we need to do, is to take the number 13195, then try and divide it by the smallest prime number; 2.

If it doesn’t divide equally, we try it with the next prime number; 3, and so on, until it divides evenly with no remainder.

So 13195 divides into 5 evenly, and we get a result of 2639.

We can retain that number 5, but since we’re only interested in the largest prime factor, we reset our divisor count to 2 and start the process again, trying to divide 2639 until we find a number that it divides evenly by, which happens to be 7.

  • 13195 / 5 = 2639
  • 2639 / 7 = 377
  • 377 / 13 = 29

On the last stage of prime factorisation, we’re trying to find a number that fits into 29 evenly, but there isn’t one, so we’re left with the prime number of 29.

We’re left with the prime factors of 5, 7, 13 and 29.

I found that the had a good article on prime factorisation, with several examples and explanations.

Here is my solution using Java

 * The prime factors of 13195 are 5, 7, 13 and 29.
 * <p/>
 * What is the largest prime factor of the number 600851475143 ?
public class Problem3 {

    public static void main(String[] args) {

    public static int solve(long number) {
        int i;

        // start dividing by 2, as that is the smallest prime number, keep going until we're trying to divide the number by itself,
        // this indicates we've finished.
        for (i = 2; i <= number; i++) {
            //We're only interested in "i" if it divides evenly by the number
            if (number % i == 0) {
                // divide number by i and re-assign, so we can start counting up from 2 again
                number /= i;
                // the for loop will increment i, however if number is divisible by i with no remainder, we want to try again.
                // for example, if we divide number 2000 by 2, we want to decrement i so we can try to divide the resulting 1000 by 2 again

        return i;

Don’t forget the “L” on the end of the number, we need to use a long as its too large to fit in an int.

The answer is 6857

BrickPi Lego robot takes its first steps!

A little while back I wrote a post about creating a python script to control a brickpi robot, now that I actually have the brickpi components, motors and cables and have actually tried it out, I’ve made a few improvements to that script to make it work.

Installing Raspbian

Firstly, I had to revisit the raspbian installation. With the brickpi bundle I bought from Dexter Industries, it came with a pre-installed raspbian SD card. I’m not sure what was wrong, but I wasn’t able to boot into it, there were startup errors regarding /etc/init.d. A quick Google didn’t help, so I decided to flash a new SD card with a more recent version of raspbian.

It’s important to note that the stock raspbian image won’t automatically work with the brickpi, as some modifications are required in order to control I/O for the motors. You can make these modifications yourself as there are instructions on the brickpi website, but it’s far easier to just download the pre-modified raspbian from dexter industries.

This was quite simple, on a mac you can erase and format an SD card using Disk Utility, after that, use these commands to create the SD card image:

diskutil list
diskutil unmountdisk /dev/disk1
dd if=2013.07.27_BrickPi.img of=/dev/disk1 bs=2m

diskutil list will show you the drives attached, in my case the SD card was disk1 but it may vary for you. It takes around 10 minutes to flash the SD card so go make a brew.

Configuring WiFi

Setting up wifi on the pi is pretty easy, I have a USB wifi adapter, so it was just a case of configuring a wireless interface, which can be done by adding the following to /etc/network/interfaces

sudo nano /etc/network/interfaces
iface wlan0 inet dhcp
wpa-ssid "NETWORK_ID_HERE"

Then do a sudo reboot

Expanding the SD card

In order to expand the root partition and make use of the entire SD card, run the following command and follow the menus to expand SD card

sudo raspi-config

Then do a sudo reboot

Setting up the brickpi dependencies

SSH onto the pi and run the following

mkdir brickpi
cd brickpi/
git clone
cd BrickPi_Python
sudo apt-get install python-setuptools
sudo python install

This will clone the BrickPi python repository (which contains a load of examples), install python-setuptools and install the brickpi module, so you can import Brickpi globally in your python scripts.

Controlling the robot

After testing out the brickpi examples, it was quite clear that I’d need to modify my original python script. I needed 2 threads.

  • Thread 1 would continually update the motors every 200ms, otherwise the motors would turn briefly and then remain still.
  • Thread 2 would process incoming commands and set the motor speeds.

Other than the threading code, the script is quite easy to follow

from BrickPi import *   #import file to use BrickPi operations
import threading
import socket
import select
import Queue
from threading import Thread
import sys

BrickPiSetup()  # setup the serial port for communication
BrickPi.MotorEnable[PORT_A] = 1 #Enable the Motor A
BrickPi.MotorEnable[PORT_D] = 1 #Enable the Motor D
BrickPiSetupSensors()   #Send the properties of sensors to BrickPi

running = True

#This thread is used for keeping the motor running while the main thread waits for user input
class BrickPiThread (threading.Thread):
    def __init__(self, threadID, name, counter):
        self.threadID = threadID = name
        self.counter = counter
    def run(self):
        while running:
            BrickPiUpdateValues()       # Ask BrickPi to update values for sensors/motors
            time.sleep(.2)              # sleep for 200 ms

brickPiThread = BrickPiThread(1, "BrickPiThread", 1)                #Setup and start the thread

class ProcessCommandThread(Thread):
    def __init__(self):
        super(ProcessCommandThread, self).__init__()
        self.running = True
        self.q = Queue.Queue()

    def add(self, data):

    def stop(self):
        self.running = False

    def run(self):
        q = self.q
        while self.running:
                # block for 1 second only:
                value = q.get(block=True, timeout=1)
            except Queue.Empty:
        if not q.empty():
            print "Elements left in the queue:"
            while not q.empty():
                print q.get()

commandThread = ProcessCommandThread()

def process(value):
    print "Processing [{v}]".format(v=value)

    # Left side
    if value == 'L-FORWARD-Start':
        print "L-FORWARD-Start"
        BrickPi.MotorSpeed[PORT_A] = 200
    elif value == 'L-FORWARD-Stop':
        print "L-FORWARD-Stop"
        BrickPi.MotorSpeed[PORT_A] = 0
    elif value == 'L-BACK-Start':
        print "L-BACK-Start"
        BrickPi.MotorSpeed[PORT_A] = -200
    elif value == 'L-BACK-Stop':
        print "L-BACK-Stop"
        BrickPi.MotorSpeed[PORT_A] = 0
    # Right side
    if value == 'R-FORWARD-Start':
        print "R-FORWARD-Start"
        BrickPi.MotorSpeed[PORT_D] = 200
    elif value == 'R-FORWARD-Stop':
        print "R-FORWARD-Stop"
        BrickPi.MotorSpeed[PORT_D] = 0
    elif value == 'R-BACK-Start':
        print "R-BACK-Start"
        BrickPi.MotorSpeed[PORT_D] = -200
    elif value == 'R-BACK-Stop':
        print "R-BACK-Stop"
        BrickPi.MotorSpeed[PORT_D] = 0

def main():
    s = socket.socket()
    #host = socket.gethostname()
    host = ""
    port = 3033
    s.bind((host, port))

    print "Server listening on port {p}...".format(p=port)

    s.listen(5)                 # Now wait for client connection.

    while True:
            client, addr = s.accept()
            ready =[client, ], [], [], 2)
            if ready[0]:
                data = client.recv(4096)
        except KeyboardInterrupt:
            print "Stopping server."
        except socket.error, msg:
            print "Socket error %s" % msg


def cleanup():

if __name__ == "__main__":

Paste that into then run the following:

sudo python

You should see some output in the terminal as it’ll print out any incoming commands. Then its up to you to connect onto that socket with a client of your choice. I’m using an android app (which I’ve detailed here), but you could use something as simple as the following Java client


public class Runner {

    public static void main(String[] args) throws IOException {

        Socket socket = new Socket("raspberrypi", 3033);

        BufferedOutputStream bos = new BufferedOutputStream(socket.getOutputStream());

        OutputStreamWriter osw = new OutputStreamWriter(bos, "US-ASCII");



Any thoughts / suggestions? Please comment below!

Installing a new Java JDK on a Mac

Updating Java on a Mac is easy, it’s just a case of installing a new JDK and recreating the symbolic link that is used to point to the current JDK.

Download the Java .dmg for mac from the Oracle website, then run through the installer.

That will install Java for you, but your default Java installation won’t be updated to point to the new version, but fortunately its easy to correct that

Open up a terminal and type

 cd /System/Library/Frameworks/JavaVM.framework/Versions/

You will probably see something like this

 lrwxr-xr-x  1 root  wheel   60 10 Dec 17:23 CurrentJDK -> /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/

As you can see, CurrentJDK is pointing to 1.6

Delete the symbolic link

 sudo rm CurrentJDK

Then recreate it and point to the version of Java you want to use as the default

 sudo ln -s /Library/Java/JavaVirtualMachines/jdk1.7.0_45.jdk/Contents/ CurrentJDK

Then if you run java -version you should now see 1.7

 java version "1.7.0_45"
 Java(TM) SE Runtime Environment (build 1.7.0_45-b18)
 Java HotSpot(TM) 64-Bit Server VM (build 24.45-b08, mixed mode)

Project Euler, problem 2, fibonacci sequence

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, …

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

Attacking this problem in using brute force, I create a left and right ints, to hold 1 and 2 respectively, I use these to walk along the fibonacci sequence.

To count along the fibonacci sequence I add the left and right together, and shift them leftwards, until I reach the desired upper limit. On each sequence number, I check if it is even and add to a total if it is.

Here is my solution using Java

public class Problem2
    public static void main(String[] args)

    public static int execute(int upperLimit)
        // since we start with 1 & 2, we can assume result always starts from 2, as it's even
        int result = 2;
        int left = 1;
        int right = 2;

        while (left + right < upperLimit)
            int temp = left + right;
            left = right;
            right = temp;
            if (right % 2 == 0)
                result += right;

        return result;

The answer is 4613732

Why all Java devs should at least consider Groovy and Spock for testing

As a developer, testing is very important. Some developers have the mindset of “Meh, I write code, testing is a QAs job”, which is pretty poor. It’s much better for the developer to be test driving their code, generally if adopted well it produces better quality code, and of course the sooner issues are caught the cheaper they are to address.

Most Java developers who are following TDD probably use mockito or powermock alongside JUnit. I’ve never been much of a fan of those combinations as I believe they involve far too much boilerplate code, and test code often becomes more verbose and harder to maintain than the actual production code itself.

After being introduced to Spock, and testing using Groovy last year, I’m absolutely sold on it and have subsequently used it on several other projects.

For the purpose of this post, I’ll base it around a service class that does some things with a domain object, via a data access layer, which is something most enterprise developers can relate to.

Heres the domain class:

public class User {

    private int id;
    private String name;
    private int age;

    // Accessors omitted

Heres the DAO interface:

public interface UserDao {

    public User get(int id);


And finally the service:

public class UserService {

    private UserDao userDao;

    public UserService(UserDao userDao) {
        this.userDao = userDao;

    public User findUser(int id){
        return null;

Nothing too complex to mention here. The class that we’re going to put under test is the service. You can see that the service is dependant on a UserDao, which is passed into the constructor. This is a good design practice because you’re stating that in order to have a UserService, it must be constructed with a UserDao. This also becomes useful later when using dependency injection frameworks like Spring so you can mark them both as Components and Autowire the constructor arguments in, but alas.

Lets go ahead and create a test class for the service (command+shift+t if using IntelliJ on a mac).

class UserServiceTest extends Specification {

    UserService service
    UserDao dao = Mock(UserDao)

    def setup(){
        service = new UserService(dao)

    def "it gets a user by id"(){
        def id = 1

        def result = service.findUser(id)

        1 * dao.get(id) >> new User(id:id, name:"James", age:27) == 1 == "James"
        result.age == 27

Here we go, right in at the deep end, let me explain what is going on here. Firstly, we’re using groovy, so although it looks like Java (I suppose it is in some respects as it compiles down to Java bytecode anyway) the syntax is a bit lighter, such as no semi-colons to terminate statements, no need for public accessor as everything is public by default, Strings for method names. If you want to learn more about groovy, check out their documentation here.

As you can see, the test class extends from spock.lang.Specification, this is a Spock base class and allows us to use the given, when and then blocks in our test.

You’ll see the subject of the test then, the service. I prefer to define this as a field and assign it in the setup, but others prefer to instantiate it in the given block of each test, I suppose this is really just a personal preference.

Creating mocks with Spock is easy, just use Mock(Class). I then pass the mocked DAO dependency into the userService in the setup method. Setup runs before each test is executed( likewise, cleanup() is run after each test completes). This is an excellent pattern for testing as you can mock out all dependencies and define their behaviour, so you’re literally just testing the service class.

A great feature of groovy is that you can use String literals to name your methods, this makes tests much easier to read and work out what it is actually testing rather than naming them as “public void testItGetsAUserById()”

Given, when, then

Spock is a behaviour driven development (BDD) testing framework, which is where it gets the given, when and then patterns from (amongst others). The easiest way I can explain it as follows:

Given some parts, when you do something, then you expect certain things to happen.

It’s probably easier to explain my test. We’re given an id of 1, you can think of this as a variable for the test. The when block is where the test starts, this is the invocation, we’re saying that when we call findUser() on the service passing in an id, we’ll get something back and assign it to the result.

The then block are your assertions, this is where you check the outcomes. The first line in the then block looks a little scary, but actually it’s very simple, lets dissect it.

1 * dao.get(id) >> new User(id:id, name:"James", age:27)

This line is setting an expectation on the mocked dao. We’re saying that we expect 1 (and only 1) invocation on the dao.get() method, that invocation must be passed id (which we defined as 1 earlier). Still with me? Good, we’re half way.

The double chevron “>>” is a spock feature, it means “then return”. So really this line reads as “we expect 1 hit on the mocked dao get(), and when we do, return a new User object”

You can also see that I’m using named parameters in the constructor of the User object, this is another neat little feature of groovy.

The rest of the then block are just assertions on the result object, not really required here as we’re doing a straight passthrough on the dao, but gives an insight as to what you’d normally want to do in more complex examples.

The implementation.

If you run the test, it’ll fail, as we haven’t implemented the service class, so lets go ahead and do that right now, its quite simple, just update the service class to the following:

public class UserService {

    private UserDao userDao;

    public UserService(UserDao userDao) {
        this.userDao = userDao;

    public User findUser(int id){
        return userDao.get(id);

Run the test again, it should pass this time.

Stepping it up

That was a reasonably simple example, lets look at creating some users. Add the following into the UserService:

public void createUser(User user){
        // check name

        // if exists, throw exception

        // if !exists, create user

Then add these methods into the UserDao

public User findByName(String name);
    public void createUser(User user);

Then start with this test

def "it saves a new user"(){
        def user = new User(id: 1, name: 'James', age:27)


        1 * dao.findByName( >> null

        1 * dao.createUser(user)

This time, we’re testing the createUser() method on the service, you’ll notice that there is nothing returned this time.

You may be asking “why are there 2 then blocks?”, if you group everything into a single then block, Spock just asserts that they all happen, it doesn’t care about ordering. If you want ordering on assertions then you need to split into separate then blocks, spock then asserts them in order. In our case, we want to firstly find by user name to see if it exists, THEN we want to create it.

Run the test, it should fail. Implement with the following and it’ll pass

    public void createUser(User user){
        User existing = userDao.findByName(user.getName());

        if(existing == null){

Thats great for scenarios where the user doesn’t already exist, but what if it does? Lets write so co…NO! Test first!

    def "it fails to create a user because one already exists with that name"(){
        def user = new User(id: 1, name: 'James', age:27)


        1 * dao.findByName( >> user

        0 * dao.createUser(user)

        def exception = thrown(RuntimeException)
        exception.message == "User with name ${} already exists!"

This time, when we call findByName, we want to return an existing user. Then we want 0 interactions with the createUser() mocked method.

The third then block grabs hold of the thrown exception by calling thrown() and asserts the message. Note that groovy has a neat feature called GStrings that allow you to put arguments inside quoted strings.

Run the test, it will fail. Implement with the following at it’ll pass.

public void createUser(User user){
        User existing = userDao.findByName(user.getName());

        if(existing == null){
        } else{
            throw new RuntimeException(String.format("User with name %s already exists!", user.getName()));

I’ll leave it there, that should give you a brief intro to Spock, there is far more that you can do with it, this is just a basic example.

Snippets of wisdom

  • Read the spock documentation!
  • You can name spock blocks such as given:”Some variables”, this is useful if its not entirely clear what your test is doing.
  • You can use _ * mock.method() when you don’t care how many times a mock is invoked.
  • You can use underscores to wildcard methods and classes in the then block, such as 0 * mock._ to indicate you expect no other calls on the mock, or 0 * _._ to indicate no calls on anything.
  • I often write the given, when and then blocks, but then I start from the when block and work outwards, sounds like an odd approach but I find it easier to work from the invocation then work out what I need (given) and then what happens(then).
  • The expect block is useful for testing simpler methods that don’t require asserting on mocks.
  • You can wildcard arguments in the then block if you don’t care what gets passed into mocks.
  • Embrace groovy closures! They can be you’re best friend in assertions!
  • You can override setupSpec and cleanupSpec if you want things to run only once for the entire spec.


Having used Spock (and groovy for testing) on various work and hobby projects I must admit I’ve become quite a fan. Test code is there to be an aid to the developer, not a hinderance. I find that groovy has many shortcuts (collections API to name but a few!) that make writing test code much nicer.

Check out the Github Gist here