public class QueryParamPreFilter extends ZuulFilter {

    @Override

    public int filterOrder() {

        return PRE_DECORATION_FILTER_ORDER - 1; // run before PreDecoration

    }

​

    @Override

    public String filterType() {

        return PRE_TYPE;

    }

​

    @Override

    public boolean shouldFilter() {

        RequestContext ctx = RequestContext.getCurrentContext();

        return !ctx.containsKey(FORWARD_TO_KEY) // a filter has already forwarded

                && !ctx.containsKey(SERVICE_ID_KEY); // a filter has already determined serviceId

    }

    @Override

    public Object run() {

        RequestContext ctx = RequestContext.getCurrentContext();

        HttpServletRequest request = ctx.getRequest();

        if (request.getParameter("sample") != null) {

            // put the serviceId in `RequestContext`

            ctx.put(SERVICE_ID_KEY, request.getParameter("foo"));

        }

        return null;

    }

}