Introduction to Ajax4Jsf
by Shunmuga Raja
27/06/2007
1) Introduction
Java Server Faces provided a Component Based Architecture for building User Interface Components for the Web Application. Ajax aims in providing Faster Response to the Client Applications by reloading only the needed Data. Wouldn't be nice to take the advantages of both Jsf and Ajax for developing Robust Web Applications. Ajax4Jsf provides solution for this. It is the integration of Java Server Faces with Ajax (which stands for Asynchronous JavaScript and Xml), thereby providing Ajax Support to the Jsf UI Components. This article attempts to provide an overview of the Ajax4Jsf Framework which is now an open Source Project in the JBoss Community.
2) What is Ajax4Jsf?
Before trying into Ajax4Jsf, it is wise to know about the various pieces of technologies upon which Ajax4Jsf is built. From the name of the Framework itself, one should identity that Ajax (Asynchronous JavaScript and Xml) and Jsf (Java Server Faces), the most two popular technologies, are embedded within it. Let us look into these two technologies first, before delving deep into Ajax4Jsf.
Java Server Faces provides a Component Based Framework for managing and developing User Interface Components in a Web Application. It also provides rich set of Functionalities that includes Event Handling, Configuring the Page Navigation Mechanism, Validation of Client Data, Data Conversion etc. It also provides a Pluggable Architecture wherein Developers can develop their own Custom User Interface Components and plug with ease into the Framework. One of the major features of the Jsf Framework is that it is not targeted to one type of Clients. It means that apart from Html Browser Clients for the Desktop, it is even possible to have Wml Browser Clients for the mobile phones.
Ajax which stands for Asynchronous JavaScript and Xml is not new. A smarter way of using the existing standards/technologies like JavaScript, Xml and Html gave birth to Ajax. Using Ajax, it is possible for the JavaScript Code to directly communicate with the Server End. The request and the response data between Client and Server is exchanged in Xml Format. One of the major advantages of using Ajax is that it is speed up the performance of the Web Application by loading only the portion of the Web Page in consideration, thereby establishing better results. For more information and applications of Ajax, refer
http://jsf.javabeat.net/articles/2007/06/ajax-functionality-in-custom-java-server-faces-component.
Now it's time to have a look on Ajax4Jsf. As one would have guessed, Ajax4Jsf is a Framework, which, when included in a Web Application will add Ajax support for the Jsf Components. Since Jsf is a Component Based Framework, it is easy to Construct Additional Components which provided Ajax Support to the Jsf Pages. So, all the Components in the Ajax4Jsf Library are nothing but extension to Jsf Components. The transparent use of Java Script Code along with Xml Http Request Objects will be taken care by the Framework itself which means that Developer don't have to mix Java Script Code into their Application. Let us look into the Internals of the Ajax4Jsf Framework in detail in the next section.
3) Ajax4Jsf Internals
Before looking into the Ajax4Jsf internals, let us look briefly into the Architecture of Jsf. It is worth to look into the Architecture of Jsf first before getting into the details.
In Java Server Faces, whenever a Client makes a Request comes for a Resource, it is intercepted by the Faces Servlet (as represented by the javax.faces.webapp.FacesServlet). This Servlet will make the Client Request that will go through the six different Life cycle Phases like View Restoration Phase, Applying the Request Values, Validation of User Inputs, Updating the Model Objects, Execution of Application and finally Response Rendering. Ajax4Jsf is a framework that adds support to existing Jsf Application. In fact, Ajax4Jsf Framework is implemented as a Filter thereby adding JavaScript function and XmlHttpObject dependencies to the existing Jsf Components. But when the Request is a Ajax4Jsf Request, the whole things changes. Specially, whenever a Request is made by the User, a Java Script Event is fired which is processed by the Ajax Engine that usually sits in the Client Side. Now it's the Job of the Ajax Engine to submit to original Request to the Ajax4Jsf, which means that the Request will be intercepted by the Ajax4Jsf Filter. Then the Conversion of the Data to the Xml Format will take place here through the various Xml Filters after which the Request is forwarded to the original Faces Servlet thereby making the Request to go through Several Phases.
In the Ajax4Jsf Framework, there are so-called Ajax Containers which represents a Tree of Components along with Request Values that is encoded and decoded during Ajax Request and Response. It is because of the availability of Ajax Engine in the Client updates to portion of Areas in the Web Page is possible.
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