package com.test.whiteboardapp;

import java.io.IOException;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
import javax.websocket.EncodeException;
import javax.websocket.OnClose;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;

@ServerEndpoint(value="/whiteboardendpoint", encoders = {FigureEncoder.class}, decoders = {FigureDecoder.class})
public class WSEndpoint {    
    private static Set<Session> peers = Collections.synchronizedSet(new HashSet<Session>());
    
    @OnMessage
    public void broadcastFigure(Figure figure, Session session) throws IOException, EncodeException {
        System.out.println("broadcastFigure: " + figure);
        for (Session peer : peers) {
            if (!peer.equals(session)) {
                peer.getBasicRemote().sendObject(figure);
            }
        }
    }

    @OnClose
    public void onClose (Session peer) {
        peers.remove(peer);
    }
    
    @OnOpen
    public void onOpen (Session peer) {
        peers.add(peer);
    }
}

package com.test.whiteboardapp;

import java.io.StringWriter;
import javax.json.Json;
import javax.json.JsonObject;

public class Figure {
    private JsonObject json;

    public Figure(JsonObject json) {
        this.json = json;
    }

    public JsonObject getJson() {
        return json;
    }

    public void setJson(JsonObject json) {
        this.json = json;
    }

    @Override
    public String toString() {
        StringWriter writer = new StringWriter();
        Json.createWriter(writer).write(json);
        return writer.toString();
    }
}

package com.test.whiteboardapp;

import javax.websocket.EncodeException;
import javax.websocket.Encoder;
import javax.websocket.EndpointConfig;

public class FigureEncoder implements Encoder.Text<Figure>{
    @Override
    public String encode(Figure figure) throws EncodeException {
        return figure.getJson().toString();
    }

    @Override
    public void init(EndpointConfig ec) {
        System.out.println("init");
    }

    @Override
    public void destroy() {
        System.out.println("destroy");
    }
}

package com.test.whiteboardapp;

import java.io.StringReader;
import javax.json.Json;
import javax.json.JsonException;
import javax.json.JsonObject;
import javax.websocket.DecodeException;
import javax.websocket.Decoder;
import javax.websocket.EndpointConfig;

public class FigureDecoder implements Decoder.Text<Figure> {
    @Override
    public Figure decode(String string) throws DecodeException {
        JsonObject jsonObject = Json.createReader(new StringReader(string)).readObject();
        return  new Figure(jsonObject);
    }

    @Override
    public boolean willDecode(String string) {
        try {
            Json.createReader(new StringReader(string)).readObject();
            return true;
        } catch (JsonException ex) {
            ex.printStackTrace();
            return false;
        }
    
    }

    @Override
    public void init(EndpointConfig ec) {
        System.out.println("init");
    }

    @Override
    public void destroy() {
        System.out.println("destroy");
    }
}