how to use a filter to add params in servlet 2.3

[Rishi Singh]

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?

[Madhav Lakkapragada]

Form my past reading on the ranch, this seems to be a good article on Filters.
Never used Filters so far......
regds.
- madhav