Question

I would like to run a search whenever a 404 is encountered. For example, a user would like to view restaurants with Italian cuisine, they would go to http://www.mywebsite.com/italian so instead of showing a custom 404 error page, I would like add a filter which first checks if a 404 would have been thrown, if so, attempt to search against a list of search items, if a match exists, forward request to that page rather than throw 404 error.

Example:

www.mywebsite.com/italian  --> www.mywebsite.com/search.do?cuisine=italian
www.mywebsite.com/london   --> www.mywebsite.com/search.do?city=london 
www.mywebsite.com/rest     --> www.mywebsite.com/show.do?rest_id=XXX

The question I guess is how would I determine if there doesn’t exists a servlet with url-mapping "/italian" or "/italian/*" within my server config?

Using (in Filter.doFilter) request.getRequestDispatcher(request.getRequestURI()) always returns a non-null value which I cannot use to determine whether the request is valid or not. I can use a 404 error statement but the result would have a response status of 404 rather than 200.

Answer 1

You can just map the 404 error page on a servlet URL pattern.

<servlet>
    <servlet-name>errorServlet</servlet-name>
    <servlet-class>com.example.ErrorServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>errorServlet</servlet-name>
    <url-pattern>/error</url-pattern>
</servlet-mapping>

<error-page>
    <error-code>404</error-code>
    <location>/error</location>
</error-page>

This allows for doing fine grained business and HTTP request/response controlling job in the servlet before displaying the desired JSP.