Thanks a lot!

So i have a new version of the interceptor-method:

    public String intercept (ActionInvocation invocation) throws Exception {
        //get the session
        Map attributes = invocation.getInvocationContext().getSession();

        // Is there a "user" object stored in the user's HttpSession?
        Object user = attributes.get(USER_HANDLE);
        if (user == null) {
            // The user has not logged in yet.

            // Is the user attempting to log in right now?
            Map parameters = invocation.getInvocationContext().getParameters()
            
            String loginAttempt = parameters.get( LOGIN_ATTEMPT);
            if (! StringUtils.isBlank (loginAttempt) ) { // The user is attempting to log in.

                // Process the user's login attempt.
                if (processLoginAttempt (request, session) ) {
                    // The login succeeded send them the login-success page.                    
                    return "login-success";
                } else {
                    // The login failed. Set an error if we can on the action.
                    Object action = invocation.getAction ();
                    if (action instanceof ValidationAware) {
                        ((ValidationAware) action).addActionError ("Username or password incorrect.");
                    }
                }
            }

            //put the address of the action called originally into the session
            String urlGoingTo = invocation.getProxy().getNamespace()+"/"+
            invocation.getProxy().getActionName()+".action";
        
            attributes.put( "GOING_TO", urlGoingTo);
            // Either the login attempt failed or the user hasn't tried to login yet, 
            // and we need to send the login form.
            
            
            return "login";
        } else {
            return invocation.invoke ();
        }
    }

It's a little nicer looking because it gets maps of the parameters and session-attributes instead of using the more clumpsy HttpSession/HttpServletRequest-classes.

The url is saved into the session (GOING_TO) and can be used in the login.jsp to redirect to where the user wanted to go originally.