Object Output Stream - In Deepth

Question

Previous Problem
- Was sending java.util.Set over ObjectOutputStream, however say the set had 4 objects in it the first tym sent, 4 objects would also be in it when recived at server side, but second tym the set was sent, say 2 of those objects were removed, there would be an output of 2 objects on the client side but still 4 on the server side.
- Answered Below by a member of the forums -
The object output stream deals with objects.
When you hand your Set object to the ObjectOutputStream, it politely hands it to the server.
When you hand the same Set object to the OOS it notices that it's seen it before, and merely sends a sharp note to the server saying "oh yes, we've seen this one before".
Which is intentional - it's so that these classes...
public class Foo1 {
Foo2 foo;
public class Foo2 {
Foo1 foo;
...don't end up getting serialised for ever as it bounced between serialising Foo1's copy of Foo2 and Foo2's copy of Foo1 and Foo1's copy of - and so on.
In order to cause the new (empty) contents of the Set to be sent to the server, you'll have to either send a suitable command string (literally "CLEAR" or something), and detect that - or just create a new empty set and send that - for example:
output.writeObject(strings.clone());
Hope that's of help.
Dave.
Haha ok now i have a similar problem again, the server now recieves the correct amount of objects in the Set, however when a bullet is updated and it sends the set again, it recives the first bullets values. For example;
4 Bullets are shot, 4 Bullets are added to the Set, 4 Bullets send to server which are sent to oposition. This is great working well, now however, the bullets are update position changed, send the set again, but x and y values changed on client side, but when recieved on server side are the values of the first instance of that bullet sent.
EG:
Client send set Bullet x = 7 y = 7
Server recives Bullet x = 7 y = 7
Client send set bullet after values in Bullets changes x = 9, y = 9
Server recieves Bullet x = 7 y = 7
See the problem?
Haha very similar to the first problem, just dont know how to get around it.
Thanks in advance Nick

Answer 1

Check the reset() method on ObjectOutputStream.
if you call reset() before sending an object I think
this does what you want.I have just written a simple example to illustrate this. It resets the OOS on 'even' sends and not on 'odd' sends. As expected, it never receives updated objects on 'odd' sends.
import java.net.*;
import java.io.*;
public class Test1
    static class Item implements Serializable
        private int index = 0;
        void inc()
            index++;
        public int getIndex()
            return index;
        public String toString()
            return Integer.toString(index);
    static public void main(String[] args)
        try
            final ServerSocket serverSocket = new ServerSocket(12345, 10);
            Thread runner = new Thread()
                public void run()
                    try
                        Socket connection = serverSocket.accept();
                        ObjectInputStream ois = new ObjectInputStream(connection.getInputStream());
                        while (true)
                            while (true)
                                try
                                    Object obj = ois.readObject();
                                    System.out.println("Received : " + obj);
                                catch (Exception e)
                                    System.out.println("Exception 1 = " + e);
                                    e.printStackTrace();
                    catch (Exception e)
                        System.out.println("Exception 2 = " + e);
                        e.printStackTrace();
            runner.setDaemon(true);
            runner.start();
            Socket s = new Socket("localhost", 12345);
            ObjectOutputStream oos = new ObjectOutputStream(s.getOutputStream());
            Item item = new Item();
            for (int i = 0; i < 10; i++)
                if ((i & 1) == 0)
                    oos.reset();
                oos.writeObject(item);
                System.out.println("Sent : " + i);
                item.inc();
            serverSocket.close();
        catch (Exception e)
            e.printStackTrace();
}