DiscoveryHostUrlFilter

DiscoveryHostUrlFilter.java

import com.netflix.zuul.ZuulFilter;
import com.netflix.zuul.context.RequestContext;
import org.springframework.stereotype.Component;

import java.net.URL;

/**
 * <i>Spring Cloud Netflix - Zuul</i> does not support <i>load-balanced</i> routing if target service has
 * context path different than {@code /}.
 *
 * Only "solution" is to use {@code zuul.<route-name>.url = http://hostname:port/context-path}, but by choosing this way
 * you will loose <b>load-balancing</b> and <b>circuit-breaking</b> capacities. That is not really acceptable.
 *
 * Following {@link ZuulFilter} is simple by-pass to enhance {@code zuul.<route-name>.url} properties to accept
 * {@code service-id} in addition to plain old {@code hostname:port}.
 * Like {@link org.springframework.web.client.RestTemplate} with
 * {@link org.springframework.cloud.client.loadbalancer.LoadBalanced} you can use following syntax:
 * {@code http://<service-id>/} or even {@code http://<service-id>/path}.
 *
 * As you can see you have now the capacity to add {@code path} after {@code <service-id>} that can be used to manage
 * target context path.
 *
 * Please track following issue https://github.com/spring-cloud/spring-cloud-netflix/issues/1235 that talk about
 * refactoring whole <i>Spring Cloud Netflix - Zuul</i> routing configuration.
 *
 * @author Thibaud Leprêtre
 */
@Component
public class DiscoveryHostUrlFilter extends ZuulFilter {

    private static final String DISCOVERY_FRAGMENT = "discovery";

    @Override
    public String filterType() {
        return "pre";
    }

    @Override
    public int filterOrder() {
        return 10;
    }

    @Override
    public boolean shouldFilter() {
        RequestContext ctx = RequestContext.getCurrentContext();
        URL url = ctx.getRouteHost();
        return !ctx.containsKey("serviceId") && url != null && DISCOVERY_FRAGMENT.equals(url.getRef());
    }

    @Override
    public Object run() {
        RequestContext ctx = RequestContext.getCurrentContext();
        URL url = ctx.getRouteHost();
        String serviceId = url.getHost();

        ctx.set("serviceId", serviceId);
        ctx.setRouteHost(null);
        ctx.addOriginResponseHeader("X-Zuul-ServiceId", serviceId);
        String path = !ctx.containsKey("requestURI") ? "" : (String) ctx.get("requestURI");
        ctx.set("requestURI", (url.getPath() + path).replace("//", "/"));

        return null;
    }
}