March - 2008 - issue > Technology
Kishore Kumar
Friday, February 29, 2008
There are many tools and technologies out there that will help you develop new generation applications. In this article we will discuss about developing Rich Internet applications using Java and OpenLaszlo.

About OpenLaszlo

OpenLaszlo is an open source platform for developing rich Internet applications. As this is being written the latest stable release is 4.0.10 and all listings in this article have been tested on this version. With OpenLaszlo you write XML files containing special OpenLaszlo tags and event handling code, also called the LZX language, to define your user interface. The event handling code is very similar to JavaScript, and so it is easy to learn and get used to. These XML files are then converted and rendered as flash movies (sw7 or sw8 files) or as DHTML code. As you already know, the flash movies will be played on a Flash Player and the DHTML code will be rendered directly by the browser.

Getting started

Installation: OpenLaszlo comes in two download options: a full server installation or just the core web application. The full server installation has a bundled Tomcat Server with it.

To install the server version simply download the OpenLaszlo server and run the installer executable. There is a separate download for windows, Unix/Linux and Mac OS X. You need to have JDK (and not just the JRE) 1.4 or above installed and available before you start the installation process.

To install just the core web application into an existing application server (or a Servlet container like Tomcat), download and pack the contents of the directory lps-4.0.10 as a WAR (Web Archive) package and deploy the WAR file into the web container. (Note that LPS stands for its former name, Laszlo Presentation Server.)

Run your first OpenLaszlo Application: For the sake of this article, I assume that you have installed the full server version of OpenLaszlo in Windows.

To begin, you need to start the server by selecting the ‘Start OpenLaszlo Server’ menu under ‘OpenLaszlo Server’ from the Start or Programs Menu. Otherwise, you may also start by navigating to the tomcat directory of Laszlo and starting Tomcat Server by running the startup.bat from the command prompt.

Once you have the Tomcat server started, open your web browser and type the url: http://localost:8080/lps-4.0.10/examples/hello.lzx. You should see ‘Hello Laszlo!’ displayed.
Debug: OpenLaszlo displays a debug frame towards the end of an LZX page. You should see this if you scroll down to the end of the ‘Hello.Laszlo!’ page. This debug frame gives you options to change compile-formats between flash video and DHTML. Just select DHTML instead of sw7/sw8 and hit compile button and you will see the same page reloaded as a DHTML page. You may also select the debug checkbox and hit compile, you should see an additional debug window where your debug messages can be printed and viewed.

OpenLaszlo features

In this section, I will introduce you to writing Laszlo programs with commonly used user interface components along with how to respond to user interface events by writing event

The window and the view component: The window and view components are containers for other components. The following code snippet shows how easy it is to create a window with OpenLaszlo.

resizable=”true” closeable=”true”>

Canvas is the container for all views and represents the viewable area of the application. You may provide values for various attributes of the canvas objects (as well as other objects) like the ‘bgcolor’ and ‘width’ attributes.
Copy paste the above code snippet into a file and name it ‘sample.lzx’. Copy this file to the my-apps folder in Server/lps-4.0.10 directory and point your browser to http://localhost:8080/lps-4.0.10/my-apps/sample.lzx. You should see the following:
A View is the most basic viewable element and every component that can be displayed on the Canvas inherits from the View component. Note that OpenLaszlo is Object Oriented and supports Object Oriented concepts like Inheritance and method overriding. The following code snippet shows a View containing a text component and a button component along with a layout manager to render the components inside the View.

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