Java sending object with ArrayList via sockets

Question

I'm a beginner in Java.

I have task to do multiplayer game. My main problem now is updating position of players. I write server and client application. I write class Players when I store ArrayList (PlayerData) and this arraylist is what I want to send via ObjectOutputStream.

In console I see that all variables are ok but when server sends and client receives packets, all var like int ID or String are updated but arraylist not.

I can't find solution, which I hope is very easy, but my bad - I can't find it. Please, Gods of Java, help me because I have been trying to fix it about 3 days.

public class Players {

private ArrayList<PlayerData> players = new ArrayList<PlayerData>();

public Players() {
    // TODO Auto-generated constructor stub
}

public Players(ArrayList<PlayerData> listData) {
    this.players = new ArrayList<PlayerData>();
    players.addAll(listData);
    System.err.println(players.get(0).getPosition().x + " " +  players.get(0).getPosition().y);
}

public void add(int port,String username,Vector2 pos)
{
    players.add(new PlayerData(port,username, pos));
}
public void update(int port, Vector2 move)
{
    for (int i = 0 ; i < players.size() ; i++)
    {
        if ( players.get(i).getID() == port)
        {
            System.err.println("Poruszam sie " + " " + move.x +  " " + move.y);

            players.get(i).move(move);
        }
    }
}
public ArrayList<PlayerData> getPlayers()
{
        return players;
}
public PlayerData getPlayer(int ID)
{
    return players.get(ID);
}
public int size()
{
    return players.size();
}
public void remove(int ID) {
    // TODO Auto-generated method stub
    if(ID <players.size())
        players.remove(ID);
}

//server function handlemove

public void handleMove(Object obj,int port) {
    // TODO Auto-generated method stub
    PacketMove packet = (PacketMove)obj;
    pos.x += packet.getPosition().x;
    pos.y += packet.getPosition().y;

    playersConnected.update(port, packet.getPosition());

    System.err.println("Move " + playersConnected.getPlayer(0).getPosition().x + " " + playersConnected.getPlayer(0).getPosition().y);
    //clients[getID(port)].send(new PacketMove(2, new Vector2(playersConnected.getPlayer(0).getPosition())));
//  broadcast(new PacketMove(getID(port), new Vector2(playersConnected.getPlayer(port).getPosition())));
    licznik +=1;
    clients[0].send(new PacketUpdate(licznik, new Players(playersConnected.getPlayers())));
}


public class PlayerData implements Serializable{
/**
 * 
 */
private static final long serialVersionUID = 4168716596929732412L;
private Vector2 position;
private String username;
private int ID = -1;

public PlayerData(int port,String username,Vector2 position) {
    // TODO Auto-generated constructor stub
    this.position = position;
    this.username = username;
    this.ID = port;
}
public String getUsername()
{
    return username;
}
public void setUsername(String username)
{
    this.username = username;
}
public Vector2 getPosition()
{
    return position;
}
public void setPosition(Vector2 pos)
{
    this.position = pos;
}
public int getID()
{
    return ID;
}

public void move(Vector2 move) {

    this.position.x += move.x;
    this.position.y += move.y;
    System.out.println(position.x + " " + position.y + " w playerdata");
}

}

Can you let us know class definition for PacketUpdate -- as looks like that is what you are sending — Sendi_t
– Sendi_t, Commented May 4, 2015 at 22:21
@user2204627 You must post it here. Otherwise the question is incomplete and liable to be deleted. And please punctuate, capitalize, and paragraph your incomprehensible mess of a question. — user207421
– user207421, Commented May 4, 2015 at 23:10

Sendi_t · Accepted Answer · 2015-05-05 16:03:35Z

You need to also list the what is the content of your send clients[0].send(new PacketUpdate(licznik, new Players(playersConnected.getPlayers())));

Also how you are sending and receiving on client and server.. only than we can exactly pin-point the issue.. Here I have listed a basic test that asserts array list of your PlayerData object is serialized. I have used junit4 -- so to run this you will need to add junit-4 jars in your classpath

based on your specific code, you can make modifications to this test to adjust..

import static org.junit.Assert.assertEquals;

import java.io.*;
import java.util.ArrayList;
import java.util.List;

import org.junit.Before;
import org.junit.Test;


public class PlayersTest  {
    private List<PlayerData> list_of_object = new ArrayList<PlayerData>();

    @Before
    public void setUp() throws Exception {
        for(int i=0; i< 10; i++){
            PlayerData p = new PlayerData(i,"", new PlayersPosition(i, i*22));
            list_of_object.add(p);
        }
    }

    @Test
    public void test() throws Exception {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(baos);
        oos.writeObject(list_of_object);

        byte[] dataToSend = baos.toByteArray();
        ByteArrayInputStream bais = new ByteArrayInputStream(dataToSend);
        ObjectInputStream ois = new ObjectInputStream(bais);
        List<PlayerData> deserialized = (List<PlayerData>) ois.readObject();
        assertEquals(list_of_object.size(), deserialized.size());

        for (int i=0; i < 10; i++){
           assertEquals(list_of_object.get(i), deserialized.get(i));
        }
    }

    public static class PlayersPosition implements Serializable {
        private double x;
        private double y;

        public PlayersPosition(double x, double y) {
            this.x = x;
            this.y = y;
        }

        public double getX() {
            return x;
        }

        public double getY() {
            return y;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;

            PlayersPosition that = (PlayersPosition) o;

            if (Double.compare(that.x, x) != 0) return false;
            return Double.compare(that.y, y) == 0;

        }

   }

    public static class PlayerData implements Serializable {
        /**
         *
         */
        private static final long serialVersionUID = 1L;
        private PlayersPosition playersPosition;
        private String username;
        private int ID = -1;

        public PlayerData(int port, String username, PlayersPosition playersPosition) {
            // TODO Auto-generated constructor stub
            this.playersPosition = playersPosition;
            this.username = username;
            this.ID = port;
        }

        public String getUsername() {
            return username;
        }

        public void setUsername(String username) {
            this.username = username;
        }

        public PlayersPosition getPlayersPosition() {
            return playersPosition;
        }

        public void setPlayersPosition(PlayersPosition pos) {
            this.playersPosition = pos;
        }

        public int getID() {
            return ID;
        }

        public void move(PlayersPosition moveTo) {

            this.playersPosition.x += moveTo.getX();
            this.playersPosition.y += moveTo.getX();
            System.out.println(playersPosition.getX() + " " + playersPosition.getX() + " w playerdata");
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;

            PlayerData that = (PlayerData) o;

            if (ID != that.ID) return false;
            if (!playersPosition.equals(that.playersPosition)) return false;
            return username.equals(that.username);

        }


    }

}

I find solution i add one line of code in function send in server. It was streamOut.reset(); Now everything works great

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