How do I add custom error pages (like Page Expired)?
In your application class that extends WebApplication, set the following in the init() method getApplicationSettings().setPageExpiredErrorPage(myExpiredPage.class). There are also some other neat settings you should check out in getApplicationSettings(), getDebugSettings(), getExceptionSettings(), getMarkupSettings(), getPageSettings(), getRequestCycleSettings(), getSecuritySettings and getSessionSettings(). See the javadoc for more information.