You can find the full source code for this website in the Seam package in the directory /examples/wiki. It is licensed under the LGPL.
The JBoss extension to the expression language allows you to call arbitrary methods, e.g.:
<h:outputText value="#{aStringVariable.concat(anotherString).concat(oneMoreString)}"/>
For more advanced String operations (not available on the java.lang.String class), see How can I operate on Strings in my templates?