How to find the desktop id for current request from a servlet filter

answered 2011-03-02 09:27:24 +0800

gekkio
899 ● 1
http://gekkio.fi/blog

As far as I know, that's impossible because ZK hasn't even started processing the request yet when your filter is invoked (ZK uses a Servlet, so it starts processing the request only after all filters have finished).
You didn't mention the use case for your filter, but you might want to consider using ZK listeners instead.
If you implement ExecutionInit and/or ExecutionCleanup you might be able to do what you want.

Note that Execution is the ZK equivalent of a HTTP request.

answered 2011-03-02 10:10:33 +0800

gekkio
899 ● 1
http://gekkio.fi/blog

Ok, I assumed you wanted to actually modify the desktop.

You are correct, dtid is the desktop id parameter. However, just because it exists doesn't mean that a valid desktop exists.
If you want to ensure there is a valid desktop available for the request, here's how to do it:

HttpSession httpSession = ... // get it from somewhere
ServletContext servletContext = ... // get if from somewhere
String desktopId = ... // read it from dtid parameter

WebApp webApp = WebManager.getWebApp(servletContext); // You don't have to do this in every request, you can read webApp in Filter.init
Session zkSession = SessionsCtrl.getSession(webApp, httpSession);
if (zkSession != null) {
  if (zkSession instanceof SessionCtrl) {
    SessionCtrl sessionCtrl = (SessionCtrl) zkSession;
    Desktop desktop = sessionCtrl.getDesktopCache().getDesktop(desktopId);
    if (desktop != null) {
      // Now you know you have a valid desktop and session for this request
      // Remember that modifying the desktop is NOT safe
    }
  }
}

Note that you cannot modify the desktop safely, so by using this method you can only check that you have a valid desktop.

If you actually want to change something or interact with the desktop, you'll have to use UiEngine updates. But that is very error prone and I really think it's a bad idea unless you know exactly what you are doing. Especially because you would be effectively doing two ZK updates in one HTTP request (one in Filter, one in Servlet). I've implemented a Servlet 3.0 API asynchronous server push using manual UiEngine updates (without the regular ZK server push), so I know from experience that it can be very difficult to get things like that work without problems.