source: src/main/java/geniusweb/profilesserver/websocket/ProfilesListSocket.java

package geniusweb.profilesserver.websocket;

import java.io.IOException;
import java.lang.management.ManagementFactory;
import java.net.InetAddress;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.UnknownHostException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.logging.Level;
import java.util.stream.Collectors;

import javax.management.MBeanServer;
import javax.management.MalformedObjectNameException;
import javax.management.ObjectName;
import javax.management.Query;
import javax.websocket.OnClose;
import javax.websocket.OnError;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;

import geniusweb.profilesserver.Constants;
import geniusweb.profilesserver.ProfilesRepository;
import geniusweb.profilesserver.events.ChangeEvent;
import tudelft.utilities.listener.Listener;
import tudelft.utilities.logging.ReportToLogger;
import tudelft.utilities.logging.Reporter;

/**
 * Returns a websocket that communicates the list of currently available domains
 * and profiles. Every time something changes, a new list of domains and
 * profiles is sent. For each new websocket the server will create one of this
 * but they all share one {@link ProfilesRepository}.
 */
@ServerEndpoint("/websocket/liststream")
public class ProfilesListSocket {

        private final Reporter log;
        /** following both final but set in {@link #start(Session)} */
        private Session session;
        private Listener<ChangeEvent> changeListener;
        private static transient String hostport = ""; // cache

        public ProfilesListSocket() {
                this(new ReportToLogger("profilesserver"));
        }

        public ProfilesListSocket(ReportToLogger reportToLogger) {
                this.log = reportToLogger;
        }

        @OnOpen
        public void start(Session session) throws IOException {
                this.session = session;
                log.log(Level.INFO, "New connection " + session.getRequestURI());

                sendupdatedProfiles();
                changeListener = new Listener<ChangeEvent>() {

                        @Override
                        public void notifyChange(ChangeEvent data) {
                                try {
                                        sendupdatedProfiles();
                                } catch (IOException e) {
                                        e.printStackTrace();
                                }
                        }
                };
                Profiles.repository.addListener(changeListener);
        }

        /**
         * Send the latest profiles to the client.
         * 
         * @throws IOException
         */
        private void sendupdatedProfiles() throws IOException {
                log.log(Level.FINER, "sending updated profiles");
                session.getBasicRemote().sendText(
                                Constants.getJackson().writeValueAsString(getDomainsProfiles()));
        }

        /**
         * @return list of domain and profile URIs, as a hashmap.
         */
        private Map<URI, List<URI>> getDomainsProfiles() {
                Map<URI, List<URI>> allprofiles = new HashMap<>();
                for (String domain : Profiles.repository.getDomains()) {
                        List<URI> profiles = Profiles.repository.getProfiles(domain).stream()
                                        .map(profile -> makeURI(domain, profile.getName()))
                                        .collect(Collectors.toList());
                        allprofiles.put(makeURI(domain, null), profiles);
                }
                return allprofiles;
        }

        /**
         * @param domain  the domain name.
         * @param profile the profile name. If null, a ref to the the domain (no
         *                profile) is needed
         * @return a URI where to get the given profile/domain.
         */
        private URI makeURI(String domain, String profile) {
                try {
                        return new URI("ws://" + getIpAddressAndPort() + "/"
                                        + getServerName() + "/websocket/get/" + domain
                                        + (profile != null ? "/" + profile : ""));
                } catch (MalformedObjectNameException | UnknownHostException
                                | URISyntaxException e) {
                        log.log(Level.SEVERE, "Failed to create profile URI", e);
                        return null;
                }
        }

        /**
         * 
         * @return name of our service, eg "profilesserver"
         */
        private String getServerName() {
                // typically something like /profilesserver/websocket/liststream
                // profilesserver is the name we're looking for
                return session.getRequestURI().getPath().split("/")[1]; // drop leading
                                                                                                                                // '/'
        }

        private String getIpAddressAndPort()
                        throws UnknownHostException, MalformedObjectNameException {
                synchronized (hostport) {
                        if (hostport.isEmpty()) {
                                MBeanServer beanServer = ManagementFactory
                                                .getPlatformMBeanServer();

                                Set<ObjectName> objectNames = beanServer.queryNames(
                                                new ObjectName("*:type=Connector,*"),
                                                Query.match(Query.attr("protocol"),
                                                                Query.value("HTTP/1.1")));

                                String host = InetAddress.getLocalHost().getHostAddress();
                                String port = objectNames.iterator().next()
                                                .getKeyProperty("port");

                                hostport = host + ":" + port;
                        }
                        return hostport;
                }

        }

        @OnClose
        public void end() throws IOException {
                Profiles.repository.removeListener(changeListener);
        }

        @OnError
        public void onError(Throwable t) throws Throwable {
                t.printStackTrace();
        }

}