source: src/main/java/geniusweb/runserver/websocket/RunningListSocket.java

package geniusweb.runserver.websocket;

import java.io.IOException;
import java.util.List;
import java.util.logging.Level;
import java.util.stream.Collectors;

import javax.websocket.OnClose;
import javax.websocket.OnError;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;

import com.fasterxml.jackson.databind.ObjectMapper;

import geniusweb.protocol.NegoProtocol;
import geniusweb.runserver.RunningNego;
import geniusweb.runserver.RunningNegotiationsRepo;
import tudelft.utilities.listener.Listener;
import tudelft.utilities.logging.ReportToLogger;
import tudelft.utilities.logging.Reporter;

/**
 * Returns a websocket that communicates the list of currently running
 * {@link NegoProtocol}s. Every time something changes, a new list of
 * {@link RunningNego}s is sent.
 */
@ServerEndpoint("/websocket/running")
public class RunningListSocket {

        private Listener<String> changeListener; // final, but only initialized in
                                                                                                // startSession.
        private Session session; // a web session, not a negotiatino session
        private RunningNegotiationsRepo repo;
        private final static ObjectMapper jackson = new ObjectMapper();
        private final Reporter log;

        public RunningListSocket() {
                this(new ReportToLogger("runserver"));
        }

        public RunningListSocket(Reporter reporter) {
                this.log = reporter;
        }

        @OnOpen
        public void start(Session session) throws IOException {
                this.session = session;

                repo = getRepo();
                changeListener = new Listener<String>() {
                        @Override
                        public void notifyChange(String data) {
                                sendUpdatedSessions();
                        }
                };
                repo.addListener(changeListener);

                sendUpdatedSessions();
        }

        /**
         * Send the currently running sessions to the client.
         */
        private void sendUpdatedSessions() {
                List<String> list = repo.list().stream().map(session -> session.getID())
                                .collect(Collectors.toList());
                try {
                        System.out.println("new running negotiations:" + list);
                        session.getBasicRemote().sendText(jackson.writeValueAsString(list));
                } catch (IOException e) {
                        log.log(Level.SEVERE, "Internal problem converting json", e);
                }
        }

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

        @OnError
        public void onError(Throwable t) throws Throwable {
                log.log(Level.SEVERE, "Internal problem converting json", t);
        }

        /**
         * FactoryMethod for testing
         * 
         * @return RunningPartiesRepo
         */
        protected RunningNegotiationsRepo getRepo() {
                return RunningNegotiationsRepo.instance();
        }

}