Tuesday, 7 July 2009

Increasing/decreasing JDev 11g ADF Faces RC page font size at runtime

A feature seen on some web sites is buttons to increase and decrease the text font size. While most browsers supply this functionality by default (eg. In Firefox you can press Ctrl plus or minus), giving web page buttons to do this can assist less computer literate users who may not now about the browser's inbuilt functions.

The solution requires a javascript routine. A quick Google on "javascript increase fontsize" returns a number of useful hits including this one by White Hat Web Design.

White Hat's code is a fairly common example available on the internet for doing just this in a standard web page.

Providing this functionality in JDeveloper 11g's ADF Faces RC requires a bit of tweaking. The following describes the bits of code you'll need.


The following code takes the White Hat javascript and tweaks it:

var fontMin=10;
var fontMax=36;
function increaseFontSize(event) {
var p = document.getElementsByTagName('span'); // here
for(i=0; i < p.length; i++) {
if(p[i].style.fontSize) {
var s = parseInt(p[i].style.fontSize.replace('px',''));
} else {
var s = 14;
if(s!=fontMax) {
s += 2;
p[i].style.fontSize = s+'px';

function decreaseFontSize(event) {
var p = document.getElementsByTagName('span'); // and here
for(i=0; i < p.length;i++) {
if(p[i].style.fontSize) {
var s = parseInt(p[i].style.fontSize.replace('px',''));
} else {
var s = 12;
if(s!=fontMin) {
s -= 2;
p[i].style.fontSize = s+'px';
First tweaks to the original code, note that each method now takes an event object, and then cancels the event on executing the javascript. While I'm not entirely over the need for this, my understanding is it hooks into the ADF Faces RC javascript engine and we'll see a bit further down in this post the usage of the clientListener tags to invoke this javascript. (Some more documentation on the ADF javascript engine would be appreciated Oracle – hint hint).

Secondly note the two commented lines. The original code searched for <p> tags, while in ADF Faces RC pages we need to search for <span> tags, as this is where ADF Faces RC places raw text.

Load the javascript into JSF

In the page we wish to include the javascript we include the following code:

...assuming you stored the above javascript in the ViewController public_html/js subdirectory as fonts.js.

(Alternatively this tag could go into your JSF template so you only need to include it once)

Note that this is in fact a Apache Trinidad component, not ADF Faces RC. As such you also need to change your JSF page's <jsp:root> tag to include the Trinidad HTML tag library as follows:

xmlns:jsp="http://java.sun.com/JSP/Page" version="2.1"

Next in order to provide buttons to call the javascript we include the following command controls on our page:

Note the use of the clientListener tag to invoke the javascript functions we defined above.

Near success

At this point if you run your page you should see the fonts scale up and down when you press the relevant commandLink button.

One thing you may notice is that if you have other text based command and go components on the page (eg. <af:commandLink> <goLink>), the text fails to grow or shrink on pressing your new buttons. This occurs because the command and go components are rendered in a HTML < href> tag rather than the <span> tag we coded in our javascript. An easy solution to this is to modify your components as follows:



As the command control now uses a normal outputText component to render the text, this in turn is rendered as a HTML <span> tag in the end HTML page and will be subject to our javascript routines results.

One other thing you might notice, is in Firefox the font fails to shrink at all. Remember that Firefox has a user preference that stops this from occurring under Tools -> Options -> Content -> Fonts & Colours -> Advanced -> Minimum Font Size, a particularly useful feature on my laptop that runs at 1 sqwillion by 1 sqwillion resolution, where I can't see a d@mned thing.

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