The Java avatar for AJAX

Anadi Misra

It used to be JSP and JSF for the web pages and embedded java codes and java objects and servlets behind the scenes. That was all java could do-give you dynamic pages and you could provide interactivity, page flow and navigation with more robustness. Then came technologies like AJAX, MXML (if you still have no clue what the latter is, remember Adobe Flex!) and frameworks such as Ruby on Rails and what followed, as they say, is history. We won't go deep into what AJAX is all about and what difference or advantages it brings over pure java only pages. We will rather zero in on this Open Source project called ZK that gives AJAX without java script. Smells like GWT (Google Web Toolkit) already? Well, just read on to find out what it actually is.

The basics

You can download the latest build from the URL mentioned in the box. The installation is pretty simple, requiring you to simply unzip the package and get started by adding the 'jars' to your 'Class-path'. The framework has a library of inbuilt components and a mark-up language known as ZUML (ZK User Interface Markup Language). This mark up language is based on XUL (XML UI Language). For more details on XUL and the RICHIE alliance, visit http://xul.sourceforge.net/mozilla.html. An AJAX-based engine handles the events, where as, the components' content synchronization is handled by the ZK engine. One thing worth mentioning here is that unlike JavaScript, the events are not handled on the client side unless the developer specially provides that functionality through a component. This is interesting as local handling of certain events certainly reduces bandwidth considerations; perhaps for the reason that the creators of the framework believe that while using JavaScript, you still have to take care of other new issues such as but not limited to replicating application data across client browser and manipulating DOM on the browser end.

ZUML

This is a rich markup language that allows you to do a lot and if the tags are not enough you can embed EL (Expression Language) and even use the 'zscript', a proprietary script provided by the framework. Full marks for page region updating as it took us just three lines of code to add a label which displays the value selected in an adjoining drop down list. Other than this, there is a rich set of attributes that can be used to compact the code further. And if that's not enough, you can even use the mark-up language to create custom components. For the religious java programmer who doesn't like playing with mark-ups, you can create ZK applications using the class libraries provided in the framework. Using these objects in the libraries available is not that cumbersome as it is simply writing the code.

The Java Way

If scripts and mark-ups are not your favorite, you can go for a java only way for creating pages. Let's look into some crucial classes and their methods, which make up the implicit objects.

The WebApp class represents the application and is the source for the implicit object 'applicationScope', which executes the 'getAttributes()' method of this class. Similarly, there are implicit objects such as event based on the class Event for handling events and their attributes.

Another important interface is Richlet. If you are creating pages without markup, your java class will be inheriting from classes that implement this interface-generally the 'GenericRichlet' class. A Richlet creates all components in response to a user's request. A detailed description of all the classes, tags, ZUML and sample code is available in the Developer Guides provided with the project.

In conclusion

Full marks for the excellent framework that provides full liberty to use either mark-ups or script or even Java code.

Source: PCQuest