[xwiki-users] Give a new image with a link

Hi, I should want a special link, in a xwiki page, so that when man clics on it, he get a new image (for instance, a clock with the hour of the clic). I suppose I need groovy. I know how to do an image with java, and I presume with groovy, but I don't understand how to embedded that in xwiki. I suppose I need to create a special servlet, but how this servlet is created and inserted in xwiki by the groovy mecanism ? Thank you for your help.