Go to the sourcedirectory org.olat.test and create a new class that extends from BasicController. We did this for you and named the class HelloWorldController.java. See the comments inside the class that give you helpful hints about the code. You have now a Controller class that listens to a template page. The HTML page (container) it listens to is specified as class var in the top of the class.

myContent = createVelocityContainer("helloworld");
       

The "helloworld.html file" you have to create in YOURPACKAGE/_content folder. And will be resolved as helloworld.html This file contains HTML and Velocity template code (For a reference of the Velocity template language see: VTL reference ). Inside the velocity template you can reference variables from your java class and also complete other components from other controllers. See for example:

myContent.contextPut("myContentVariable", myString );
       

The variable "myContentVariable" is accessible it the "helloworld.html" by typing "$myContentVariable" (without the capitals!)

Now we cover the PackageTranslator (translator) object which got automatically created for our controller. It is responsible for translating the content to the language the logged in user choosed. The translator looks for an other file that you have to create in YOURPACKAGE/_i18n. You can access it everywhere in your controller by calling getTranslator().translate("yourKey") LocalStrings_en.properties . This are java properties files where you can specify "key = value" pairs for the string you like to have translated.

You should now have all needed stuff: A controller class where you listen to your action. A velocity page that produces HTML output and a LocaleStrings_**.properties file for each language.

As there is no direct URL that you could enter in the browser to access you newly created content we have to "enable" it somewhere else. Excursus: OLAT URL's explained. Each link in OLAT is unique and gets dynamically generated for every page. The URL's contain the dynamically added component id and also an timestamp that gets incrementet with each click. So every OLAT URL is only valid once. This makes development of applications much easier as you do not have to worry about actions sended twice.

For testing purposes we add our content in the testing tab of the main navigation. To turn on this tab enable it in by uncommenting it in the "olat-extension.xml" file and restart OLAT. Make sure you also enabled the OLAT debug mode in the build.properties file. You find the olat-extensions.xml file under /webapp/WEB-INF/olat-extensions.xml. You should now see the tab "testing" and a menu (left) with several links to teststuff. You also see a link named "Hello World". Clicking this link will create our controller and show our content in the content area of OLAT. But how do I add a link to this menu?

Sure, we have to find the appropriate controller and add a link there and listen to the event the link produces and create our own controller. More or less the same we did in the HelloWorldController. But first we need to find the right controller out of many. There is a handy feature in the debug mode of OLAT that helps in this case. In the OLAT footer you will find a link called "Debug rendering: maxi, mini, off". Switch on render debug in the mini mode and you can hover over the content to get usefull information about each component. Hover over the leftside menu top title and a layer will appear. Look for listener and you will find org.olat.test.TestingMainController. This controller listens to the links in the left side menu. This mean that this is the right place to add our "Hello World" link.

If you open TestingMainController you will see that it consists off the same structure as our own controller. It has an constructor where translator object gets created and also an velocity container. You will find also an event method that listens for events to this controller. See inside the source and you will find the place where the link is added to the menu tree and where the event is handeld.

Create file structure

xy.test.demoextension
 controller
 _content
 _i18n
 _static
 HelloWorldExtension.java
      

Copy files to folders. The HelloWorldController to the controller folder and the properties files to the _i18n folder. Make sure you rename the "LocalStrings.properties" files to "LocalStrings_xy.properties" where "xy" stands for the country code like "en" for english as they are now all in the same folder. The images and optional css (Stylesheet) files belong to the _static folder.

Let's now create the Extension class. The extension class is responsible for creating an instance of our HelloWorldController and also to provide a visible link in the layout. Every Extenstion has therefor to implement the Extension interface. The only interface method "getExtensionFor()" is looking in a Hashmap for our extension that is is registered in the olat_extension.xml file. See below for an example. To add our extension to the ExtensionElements we have to add it first. We create a ExtensionElements object, that holds only objects of type ExtensionElement (see the table Section 3.3.2.1, “Extension points” at the beginning of the chapter for a list of the know ExtensionElement's). The HelloWorldExtension uses the ExtensionPoint ActionExtension which adds a link to the menu in the user "Home". The ActionExtension in our example is done with an inner class for brevity.

The only thing left is to export the extension as a jar file put it in the olat lib directory and enable your extension in the global olat_extension.xml file (see below) and restart olat and your done! If you consider sharing your extension with the OLAT community send your jar to the developer mailinglist and we will include it in OLAT or provide a download link on www.olat.org. Your help is very welcome and do not hesitate sending us your extension or ask questions on how to create one!