Webapps using Jahia Api

Hello,

I was just wondering what is the best way to import jahia packages from my webapp classes, for instance to get the Jahia user names :
 <% 
      JahiaUserManagerService jums = ServicesRegistry.getInstance().getJahiaUserManagerService();
      Vector v = jums.getUserList();
      Iterator it = v.iterator();
      while(it.hasNext()){
         out.println(jums.lookupUser((String)i.next()).getName());
      }
  %>

Do I have to create a new template just for that, so that it is in Jahia context and get the Jahia Api ?
Also do I put in the jar (the one containing agenda.class in template  guide chap 7)
only the classes of my webapp or all the directory (WEB-INF, web.xml,  jsp...) ? 
 I read quickly the template guide (I don't need to create new templates) but  I'm not very  sure about  it...

Thank you. 

Baptiste