Spring MVC speaking Json or XML

In Spring MVC we can find a nice way of resolving view by type of request. This class is called ContentNegotiatingViewResolver.

It uses the requested media type to find correct View for a request. Task to pick most appropriate view is done by ViewResolvers that are either set expilicty or are taken from application context.

Here is an example of ContentNegotiatingViewResolver with JSON an Xml views provided:

<bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
    <property name="order" value="1"/>
    <property name="mediaTypes">
            <entry key="json" value="application/json"/>
            <entry key="xml" value="application/xml"/>

    <property name="defaultViews">
          <!-- JSON-->
          <bean class="org.springframework.web.servlet.view.json.MappingJacksonJsonView"/>

          <!-- XML-->
          <bean class="org.springframework.web.servlet.view.xml.MarshallingView">
                  <bean class="org.springframework.oxm.xstream.XStreamMarshaller">
                      <property name="autodetectAnnotations" value="true"/>

MappingJacksonJsonView is a View that renders JSON content by serializing the model for the current request using Jackson’s ObjectMapper.

For Xml view we can use Jaxb or XStream. Not much difference beetween them: http://blog.bdoughan.com/2010/10/how-does-jaxb-compare-to-xstream.html

Now different types of call to application will cause different return types:
http://localhost/ingredient/list.xml , XML file.
http://localhost/ingredient/list.json , JSON file.
http://localhost/ingredient/list, default view resolver.

There are also other View resolvers like for RSS, velocity or freemarker available.You can find them in: org/springframework/web/servlet/view package.


Postgresql vs MySql

In previous project we were using DRBD to achieve high avalibility on postgresql 8 database. DRBD offers file system replication – all changes to a file system are mirrored to a file system residing on another server.
After many problems with DRBD split brain we decided to find better replication solution.
As postgresql didn’t had synchronus master-slave replication at this time we decided to go for MySql as we already had experience in MySql replication.

Next step was to migrate from postgresql to MySql. During this I found two minor cons of MySql I wasn’t aware of before:

MySql’s strange unicode support

MySql stores UTF-8, using 3 bytes per character (not 4 as you’d expect). It means that it doesn’t support any Unicode characters which would require 4 bytes in UTF-8.
Someone might ask who will need to store those kind of characters anyway. Here is our example.

We were using hashing mechanism based on generated seed. Seed was string generated from numbers in rage from 0 to integer maximum value. So some of our seeds for passwords had 4 bytes characters in it. No way to store it in Mysql.

No support for miliseconds in MySql

MySQL doesn’t support millisecond / microsecond precision. There is not type to store such values. Only way is to use String to store such timestamp. But this will be less eficient that integers in timestamp and more difficult to map in ORM.

PostgreSQL has an interval data type. It is capable of storing an interval of up to 178,000,000 years. Precision is maximum 14 digits. So we can measure time precisions from year to microsecond precision.


So finally we abandoned MySql and decided to wait for new Postgresql version that came with repolication:

Finally we implemented PostgreSQL’s replication using build in features of 9.1 version with use of readable standby (pgpool)


As postgresql reached his maturity level long time ago and now is even more reach in features that MySql I would recommend it for opensource projects. Another important thing is that it’s free. No special community versions and licencing problems and all the features are always there.

Travis, Code Climate, BuildCoint – ideas for better quality

Travis http://travis-ci.org/

Travis is a younger brother of Jenkins. Its a distributed build system for the open source community.
From may 2012 ( after fixing issue 242) its also avalible for your organization repositories (if you have admin rights).
You can connect it to you github project using service hooks.

Codeclimate https://codeclimate.com/

Code Climate is service providing software metrics for Ruby apps. Since Jul 10th, 2012 it became free for Open Source project. It offers realtime metrics, activity feeds and email reports.

Since its free I added one of my first ruby project repository to see some metrics:

So metrics on current state of project for all classes was A. Code climate discovered one code smell: “Complex method” for one of methods. Beside this its showing LOC, code duplicates and some other metrics.

Code climate supports badges like travis. On project page there are snippets make it easy to add a link to Code Climate from your README.

BuildCoin http://buildcoin.com/

And last is most interesting project named: BuildCoin.
As their page says its: “The Ultimate CI Game”. Project is in beta mode still and i am waiting for invitation code. The idea is quite simple: platform offers real-time dashboard and based on it you can setup some bonus games.
I imagine it would be something like: 100 coins for team if all major bugs will be fixed till the end of month.
Or 50 coins for improving code coverage to 80%. I think that after some practise with bonus systems its possible to develop some nice motivational bonus system for developers and have a lot of fun from daily jobs.

Test Data Builder pattern

Creating test object using they default constructors is very annoying when we have complicated model and variety of different test cases to cover. We can use with help of Creation Class or Object Mother pattern.

With them we can simplify object creation by reducing number of constructors and replace them with creation methods Then we have something like this:

Person person = PersonCreator.createPerson();
Person person = PersonCreator.createPersonWithAccount(Account accont);
Person person = PersonCreator.createPersonWithNameAndAccount(String name, Account account);

But those classes can become cluttered with every variation of object creation method that we use in unit testing. Then its very hard to find right one and we are ending creating new ones for every slightly different object.

Test Data Builder pattern for the rescue.

The main point of the Test Data Builder pattern is to allow to create an object with specific part of his data – the data that are significant to the test. Those data creation should be visible in “given” part of test and avalible for assertion.
The rest of them for which test don’t care should not be visible in test because they distract from actual test case. For this part of object data the builder will provide safe defaults.

This way test using Test Data Builders beacomes more concise and readable:

Person person = new PersonBuilder().build();
Person person = new PersonBuilder().withName("Bob").withoutAccount().build();

Builder source code:

public class PersonBuilder extends Builder{
	private Person person;
	public PersonBuilder() {
		person = new Person();
	public PersonBuilder withId(String id){
		return this;

	public PersonBuilder withName(String name){
		return this;
	public PersonBuilder with(Account account) {
		return this;

	public PersonBuilder withoutAccount() {
		person.setAccounts(new ArrayList());
		return this;

	public Person build(){
		return person;

With builder we can create some basic predifined builder object to decrease duplication. They can be modified for need of test using “withXXX” and “withoutXXX” methods:

//sample person object fits most of the test cases
Person person = aPerson().build();
//can be easly modified if needed
Person person = aPerson().withoutAccount().build();

For better readability use short version of method names for example:
instead of:





For sure builder pattern can reduce duplications in your test code and improve readability. But it needs some additional coding to create builders structure.
If you have complicated model you can use on of automated tools to generate builders code:

For Idea there is refactoring named “replace-constructor-with-builder”. But it uses “set” instead of “with” prefix convention. For more fluent generator you can use
Eclipse: fluent-builder-generator
Idea: Builder Generator

Here you can find example of builder implementation github.com/michal-lipski/mongodb-spring-data/:

Page Object pattern with selenium WebDriver

End to end or acceptance testing is most dificult part of testing lifecycle. In most cases it involves some GUI testing. People tend to treat test code as some less importatnt part of system and pay more attention to quality an readability when the test code main priority is that should be easy to understand and clear.

Here i will shortly describe Page Object patter that keeps our GUI testing code clean and easy to maintain.

Source code to this article available at github:

Page Object pattern

A Page Object models UI page as object within the test code. This reduces the amount of duplicated code and centralizes web page data.It helps a lot with refactoring when UI changes which tends to happen very often.

Main concepts of Page Objects:

  • the public methods of Page Object should  represent the services that the page offers
  • hide all the internal details of the page (locators,elements ids,Urls) in Page Object
  • expose only services that page offers as a public methods
  • don’t make assertions in Page Object
  • sevice methods should return other Page Objects to reflect application flow
  • make sure that corresponding web page is fully loaded when you return Page Object
  • model different services for different results of one action

Page Object representing login page with login functionality covered:

public class GitHubLoginPage extends GitHubPage {

    public String getUrl() {
        return "/login";
    public void login(String login, String password) {

We can see that the login service method code looks complicated because of direct use of string literals to find elements on page. If we use those elements in other methods probably this would lead to introducing some constants. But there is a better way to do this with Selenium PageFactory.

Selenium WebDriver and PageFactory

PageFactory helps to remove some boiler-plate code from your Page Objects. Instead of declaring String describing element location we use WebElements.
So instead of:


we have:


To connect web page element with Page Object element we use @FindBy annotation:

WebElement loginField;

WebElement passwordField;

WebElement errorBox;

Using findBy annotation we can describe how selenium should search for our element on page. We can search by id, name, className, css, xpath expression and others.
Before we can use those elements we have to inintialize our Page Object class.

GitHubLoginPage page = PageFactory.initElements(driver, GitHubLoginPage.class);

Putting it all together

Page Object give us ability to build fluent calls reflecting user interaction with application. Its clear to read and reduces complexity of test method.

Here is final version of a Page Object representing github login page.
It extends base page which have common code for initialization of PageFactory and implementation of wait until page is loaded. Wait condition is based on getPageLoadCondition() implementation delivered by subclasses.

public class GitHubLoginPage extends GitHubPage {

	@FindBy(id = "login_field")
	WebElement loginField;

	@FindBy(name = "password")
	WebElement passwordField;

	@FindBy(name = "commit")
	WebElement commitButton;

	@FindBy(className = "error_box")
	WebElement errorBox;

	protected ExpectedCondition getPageLoadCondition() {
		//condition for full page load 
                return ExpectedConditions.visibilityOf(loginField);

	public String getUrl() {
		return "/login";

	public void login(String login, String password) {

	public boolean isLoginError() {
		return errorBox.isDisplayed();

	public String getErrorMessage() {
		return errorBox.getText();

And test method:

public void should_not_login_with_wrong_credentials() {
	GitHubLoginPage loginPage = new GitHubHomePage().open().goToLoginPage();
	loginPage.login("user", "password");