Tuesday, March 09, 2010

AJAX decoration: using jQuery Metadata for portlet AJAX

I recently examined a JSR 168 portlet which tackled the thorny area of AJAX in a Portlet ( incidentally the portlet I was looking at is the Jasig Calendar Portlet ). The technique used makes all AJAX requests into POSTs which are then passed via the portal and a redirect to a servlet to acquire the desired response. I am not new to JSR 168 portlets and have personally produced several portlets over the past few years. I have also solved the AJAX in a Portlet problem but in a completely different way. The solution I developed I am calling AJAX decoration and relies on the jQuery Metadata plugin. I think both techniques have their merits and possibly could be applicable to different scenarios. I will attempt to illustrate my solution with a simple example app (note this example is not an actual portlet and will work in your servlet container of choice).

The structure of each of my "portlet" JSPs in my example is something like this:


<html xmlns="http://www.w3.org/1999/xhtml">
<script type="text/javascript" src=""jquery-1.3.2.min.js"><!--" --></script>
<script type="text/javascript" src=""jquery.metadata.js"><!--" --></script>
<div id="content-area">


<script type="text/javascript">
var pageContext = "${pageContext.request.contextPath}";
var targetArea = "div#content-area";
<script type="text/javascript" src=""ajaxDecorated.js"><!--" --></script>


<%@ include file="header.jsp" %>
<h1>Some Page</h1>

<!-- Content goes here -->

<%@ include file="footer.jsp" %>

Notice that we will be using a consistent target area for our AJAX loaded content; in this case a div with the ID of "content-area". The jQuery Metadata plugin makes it possible to read data stored within CSS classes, doing this is a relatively clean way of storing data within our page. In this approach the content links are decorated with data and in turn this data is used to assign appropriate AJAX behaviour.

For a typical link using a GET we could use:

<a href=""page1.jsp"" class="ajaxRenderURL {link: '/page1.jsp'}">page 1</a>

For form submission we could use:

<form action="page2.jsp" class="ajaxActionURL {link: '/page2.jsp'}">
<input type="submit" />

The magic happens in the "ajaxDecorated.js" file. When the page initially loads initPage() is invoked which attaches AJAX loading behaviour to links and forms.

$(document).ready(function() {

function setupLinks(){
var data = $(this).metadata();
var loadlink;
var tsSeparator = "&";
if(data.link.indexOf("?") == -1){
tsSeparator = "?"
if(!data.link.match("^" + pageContext)){
loadlink = pageContext + data.link + tsSeparator + new Date().getTime() + " " + targetArea;
} else {
loadlink = data.link + tsSeparator + new Date().getTime() + " " + targetArea;
$(targetArea).load(loadlink, null,
function () {
return false;

function setupForms(){
var data = $(this).metadata();
var formdata = $(this).serializeArray();
var loadlink;
if(!data.link.match("^" + pageContext)){
loadlink = pageContext + data.link + " " + targetArea;
} else {
loadlink = data.link + " " + targetArea;
$(targetArea).load(loadlink, formdata,
return false;

function initPage(){

This technique adds AJAX to a web page in an unobtrusive way. In this simple example the URLs loaded by AJAX and those that would be loaded without are the same (page1.jsp, index.jsp etc). However, in an environment where the AJAX URLs and web page URLs are likely to be different or even change dynamically (such as in a portal) then this technique is equally applicable.


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