Modifying HttpServletRequest parameters with a Servlet Filter doesn't seem to work

Question

I need to remove/modify some of HttpServletRequest parameters. I'm trying to do so by using a Filter based on the question I posted a few days ago.

In the Filter, I'm trying to wrap the HttpServletRequest by inheriting the HttpServletRequestWrapper class as follows.

private final static class FilteredRequest extends HttpServletRequestWrapper {

    public FilteredRequest(ServletRequest request) {
        super((HttpServletRequest) request);
    }

    @Override
    public String getParameter(String paramName) {
        return super.getParameter(paramName);
    }

    @Override
    public String[] getParameterValues(String paramName) {
        return super.getParameterValues(paramName);
    }

    @Override
    public Map getParameterMap() {
        Map<Object, Object> parameterMap = new HashMap<Object, Object>();
        Map originalParameterMap = super.getParameterMap();

        for (Object o : originalParameterMap.entrySet()) {
            Map.Entry<Object, Object> pairs = (Entry<Object, Object>) o;
            parameterMap.put(pairs.getKey(), pairs.getValue());
        }
        return parameterMap;  //Returning a modifiable ParameterMap.
    }
}

It's an inner class within the Filter class. In the doFilter() method,

chain.doFilter(new FilteredRequest(request), (HttpServletResponse)response);

the constructor of the above class is being invoked (that wraps the request).

---

Now, I expect any of request parameters to modify/unset in my Spring MVC controller class. I'm trying to remove the parameter in the controller class as follows.

Map requestMap=request.getParameterMap();
requestMap.remove("txt_country_name");

Alternatively,

requestMap.put("txt_country_name", null);

Accordingly, the request parameter txt_country_name should be removed from the HttpServletRequest but it isn't removed (nor it throws any exception like "No modifications are allowed to a locked ParameterMap"). What am I missing here? Am I following a wrong way?

By the way, Making/using a request attribute all the time through out the entire application doesn't seem to be the best solution.

[I need to remove/modify request parameter within the Spring MVC controller class and not within the Filter itself]

Answer 1

Your remove method modifies the mutable map returned by getParameterMap(). But the next call to getParameterMap() reconstructs a new mutable map containing all the parameters of the wrapped query.

The mutable map should be constructed when the FilteredRequest is constructed, and it should be stored in an instance field.