Spring boot HandlerInterceptor loadbalancing

Question

I'm implementing a (sort of) load balancing HandlerInterceptor using Spring Boot.

public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
    String uri = request.getRequestURI();
    if (shouldUseServer1(uri)) {
        response.sendRedirect(server1Uri);
    } else {
        response.sendRedirect(server2Uri);
    }
}

The idea is, that based on the url, we either redirect to one service or another. The application doesn't have any explicit RequestMappings (yet).

Now the problem is, when the interceptor is called, the request is redirected to the default Spring error handler. As a result the URI stored in the HttpServletRequest is replaced by /error (effectively denying the access to the original URI).

Is there any way to intercept a request before it is rerouted to the error handler (or to get the original uri)?

Community · Accepted Answer · 2017-05-23 11:51:45Z

1

EDIT:

Because of the way Spring MVC handles requests with no mapping, you'll either need a filter:

@Component
public class CustomFilter implements Filter {

    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {

        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;

        request.getSession().setAttribute("ORIGINAL_REQUEST_URI", request.getRequestURI());
        chain.doFilter(request, response);

        // alternatively, ignore the last 2 lines
        // and just do your redirects from here 
        // and don't continue the filter chain
    }

  @Override
  public void destroy() {}

  @Override
  public void init(FilterConfig arg0) throws ServletException {}

}

Otherwise, if you'd rather not rely on the session, you'll need to make the DispatcherServlet throw an exception in case no handler mapping is found, and then send the redirect from a @ControllerAdvice error handler:

@ControllerAdvice
class NoHandlerFoundExceptionExceptionHandler {

  @ExceptionHandler(value = NoHandlerFoundException.class)
  public ModelAndView
  defaultErrorHandler(HttpServletRequest req, NoHandlerFoundException e) throws Exception {
    String uri = // resolve the URI
    return new ModelAndView("redirect:" + uri);
  }
}

To avoid duplication, you may want to have a common class that you'll call from both the interceptor and the error handler.

edited May 23, 2017 at 11:51

CommunityBot

11 silver badge

answered Sep 2, 2016 at 14:52

Miloš Milivojević

5,3993 gold badges29 silver badges41 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

irundaia Over a year ago

The redirect works fine. The problem is that I need the original URI from the request. In case there is no RequestMapping for the original URI, Spring will automatically redirect(?) to the default error controller. This redirection also changes the URI in the HttpServletRequest to /error (or some such). As a result, I can no longer access the original URI (to determine where I need to redirect to). My current workaround is to have a simple controller with a RequestMapping(path = "**"), but that seems like a dirty hack.

Miloš Milivojević Over a year ago

Ah, sorry, from your description I understood that the redirection to /error is happening in spite of the interceptor's redirect. I'll update my answer then, I think you should be okay with having a Filter that just saves the original request URI as a request attribute.

Miloš Milivojević Over a year ago

There, hope that helps. Your way of using a controller definitely requires less work and if I may be frank, probably is less of a hack :) Also, if you're just doing redirection, you're probably better off with a Filter implementation instead of using an interceptor/controller approach.

irundaia Over a year ago

It did help. Thanks a bunch for the effort :)

Miloš Milivojević Over a year ago

Don't mention it, I learned a few things along the way, too :)

Collectives™ on Stack Overflow

Spring boot HandlerInterceptor loadbalancing

1 Answer 1

5 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related