Question

I always wondered why there exists no removeParameters() method in Servlet API.
What could be the motive behind this design?
Here is a scenario: I am posed with a challenge in a proprietary MVC framework that I am compelled to use. This framework uses a Controller Servlet that hosts an algorithm in it’s post method:

doPost() {
//create instance of action - just like struts action
action.init
action.preexecution
if(redirection state is not set)
action.process
action.postprocess
action.finish
}

The only way I can skip process of any particular action would be by setting a redirection url. The Controller Servlet is FINAL. Now, when I do a requestdispatcher.forward from say the preexecution method of an action, the controller will go ahead and execute the rest of the methods and not skip the rest. I cannot change this behavior, neither can I set the redirect, coz I need to do a forward. It works fine as long as I am not forwarding request to the same action. When a request is forwarded to the same action, the http parameters are all the same. This would take it into a never ending loop. Hence, I am compelled to add extra parameters indicating that it is a repeat request and should be treated differently.
Not sure if my problem made sense, but thought this is a good forum to post the same.

Answer 1

EDIT: McDowell reminded me of HttpServletRequestWrapper, so I’m changing the below to make it a little less work… Thanks McD!

You can decorate the request to “hide” parameters you don’t want and/or add extra parameters.

Something like (off the top of me head — no compiling so the API might be a tweak off…)

public class MyParameterHider extends HttpServletRequestWrapper {
    public MyParameterHider(HttpServletRequest request) {
        super(request);
    }
    public String getParameter(String name) {
       if ("parameterToHide".equals(name))
           return null;
       return realRequest.getParameter(name);
    }
    // similar for getParameterNames and getParameterMap - don't include the hidden parm
    // all other methods are strictly pass-through and are automatically
    //   handled by HttpServletRequestWrapper
}

In your forward, just wrap the request in a ParameterHider when calling doFilter:

dispatcher.forward(new MyParameterHider(request), response);

Patterns FTW!

Hope this helps!