16.5. Themes

Seam applications are also very easily skinnable. The theme API is very similar to the localization API, but of course these two concerns are orthogonal, and some applications support both localization and themes.
First, configure the set of supported themes: 
<theme:theme-selector cookie-enabled="true">
  <theme:available-themes>
    <value>default</value>
    <value>accessible</value>
    <value>printable</value>
  </theme:available-themes>
</theme:theme-selector>
The first theme listed is the default theme.
Themes are defined in a properties file with the same name as the theme. For example, the default theme is defined as a set of entries in default.properties, which might define: 
css ../screen.css template /template.xhtml
The entries in a theme resource bundle are usually paths to CSS styles or images and names of Facelets templates (unlike localization resource bundles which are usually text).
Now we can use these entries in our JSP or Facelets pages. For example, to theme the stylesheet in a Facelets page: 
<link href="#{theme.css}" rel="stylesheet" type="text/css" />
Or, where the page definition resides in a subdirectory: 
<link href="#{facesContext.externalContext.requestContextPath}#{theme.css}" 
      rel="stylesheet" type="text/css" />
Most powerfully, Facelets lets us theme the template used by a <ui:composition>: 
<ui:composition xmlns="http://www.w3.org/1999/xhtml"
    xmlns:ui="http://java.sun.com/jsf/facelets"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:f="http://java.sun.com/jsf/core"
    template="#{theme.template}">
Just like the locale selector, there is a built-in theme selector to allow the user to freely switch themes: 
<h:selectOneMenu value="#{themeSelector.theme}"> 
  <f:selectItems value="#{themeSelector.themes}"/> 
</h:selectOneMenu> 
<h:commandButton action="#{themeSelector.select}" value="Select Theme"/>