Jersey Grizzly REST service not visible outside localhost

I'm trying to write a REST service in java using Jersey and Glassfish Grizzly. I have a very simple case working internally, but can't seem to call on the server from an external address. I've tried using a variety of different pairs of machines with externally visible IP's, and tried specifying the actual IP address in the server instead of localhost, but nothing works. I'm somewhat loosely following the official user guide here. My resource:

package resources;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;

@Path("/simpleREST")
public class SimpleRESTResource
{
    @GET
    @Produces("text/plain")
    public String getMessage()
    {
        return "Message from server\n";
    }
}

And the server:

import java.io.IOException;
import java.net.URI;

import javax.ws.rs.core.UriBuilder;

import org.glassfish.grizzly.http.server.HttpServer;

import com.sun.jersey.api.container.grizzly2.GrizzlyServerFactory;
import com.sun.jersey.api.core.PackagesResourceConfig;
import com.sun.jersey.api.core.ResourceConfig;


public class Main
{
    public static final URI BASE_URI = UriBuilder.fromUri("http://localhost").port(9998).build();

    public static void main(String[] args) throws IOException
    {
        System.out.println("Starting grizzly...");
        ResourceConfig rc = new PackagesResourceConfig("resources");
        HttpServer myServer = GrizzlyServerFactory.createHttpServer(BASE_URI, rc);
        System.out.println(String.format("Jersey app started with WADL available at %s/application.wadl\n" +
                "Try out %s/simpleREST\nHit enter to stop it...", BASE_URI, BASE_URI));
        System.in.read();
        myServer.stop();
    }
}

On the same machine, I can successfully in