Tim Panton wrote:
>
> I am trying to use the 'new' filter api to add a parameter to a
> request before a servlet is invoked. My first try involved
> calling getParameterMap()and doing a put() into it. It seems
> that map is locked readonly. So now I'm looking at
> HttpRequestWrapper but to use that I think I will have to
> emulate the whole parameter behaviour just to add a value. has
> anyone done this before, or can point me at an example?
You might be able to do something container-specific - cast the
ServletRequest to some container implementation class which gives
you access to a setter. I haven't investigated that.
The only way I could see, using the API, was to extend
HttpServletRequestWrapper and override the parameter methods. If
you know that your added parameter name won't ever conflict with
any of the original request parameters (or any added during an
include or forward), I think it can be fairly straightfoward. If
you want to merge values, you have to do a little more work.
Here's a version of one of the methods; the others are even more
straightforward.
public Map getParameterMap()
{
Map parentMap = super.getParameterMap();
if (parentMap.size() == 0 && mParameters.size() == 0)
return Collections.EMPTY_MAP;
if (parentMap.size() == 0)
return Collections.unmodifiableMap(mParameters);
if (mParameters.size() == 0)
return parentMap;
Map paramMap = new HashMap(parentMap);
paramMap.putAll(mParameters);
return Collections.unmodifiableMap(paramMap);
}
Gennis
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