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doFilter doubt?

Joe Harry
Ranch Hand

Joined: Sep 26, 2006
Posts: 10032


The following piece of code is from the HFSJ book,

public void doFilter(ServletRequest req, ServletResponse response, FilterChain chain) throws IOException, ServletException{
HttpServletRequest request = (HttpServletRequest) req;
HttpSession session = request.getSession();
Object user = session.getAttribute("user");
if (user!=null){
UserRequest ureq = new UserRequest(request, user);
chain.doFilter(ureq, response); //Line 28
RequestDispatcher rd = request.getRequestDispatcher("/login.jsp");
rd.forward(request, response);

The questions, Which is true,

Five options were give, and I'm not able to understand the explanation given for the following option,

Line 28 is invalid because request must be passed as the first argument...and they have given the reason for this option as "it is valid for a filter to wrap a request (note that UserRequest must implement ServletRequest)

I'm not able to understand the bold part. Can anyone please explain!

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Ali Gohar
Ranch Hand

Joined: Mar 18, 2004
Posts: 572
You can wrap the request/response object in Filter before passing it on. doFilter takes ServletRequest and ServletResponse as an argument so you will have to extend your request/response wrapper class with these interfaces in order to pass them as arguments in doFilter method.

See Servlet 2.4 Specs page 52 "Wrapping Requests and Responses"
Joe Harry
Ranch Hand

Joined: Sep 26, 2006
Posts: 10032


Can you please be a bit elaborate on this??
I agree. Here's the link:
subject: doFilter doubt?
It's not a secret anymore!