How to connect n clients to a server?

[chyrl]

Greetings,

I have encoded the program of client/server chat using ObjectStream - [Output/Input].
Running both client and server went well, both can communicate.
But when I open another client, the another client cannot connect to the server.

What pseudocode I am to follow to enable that another client to communicate to the server without closing the connection between the first client?

Thanks

Note: Thread cross-posted on Oracle Forums

[Norm]

In the server, have a loop that waits for a connection.
When it gets a connection, create a thread to process that connection and loop back to wait for the next connection. There will be one thread for each connection.
At some point you may need to set a limit on the number of threads running.

[chyrl]

In the server, have a loop that waits for a connection.

The server has a loop open for new connections.

When it gets a connection, create a thread to process that connection and loop back to wait for the next connection. There will be one thread for each connection.

Am I to use the Thread class? (Are there other like SwingWorker?)

At some point you may need to set a limit on the number of threads running.

Isn't that the jobs of the backLog of the ServerSocket class?

[Norm]

I used the Thread class in my server.
I never had more than 3 clients so I don't know what happens with more.

[chyrl]

Ok I'll try that logic.
Anyways, what the pseudocode inside the thread? May I know?

[chyrl]

@Norm:
Did you take a notice to what computers was connected to the servers?
Like the os.name property?

[Norm]

what computers was connected to the servers

The clients were all local (on same computer as server)

[chyrl]

The clients were all local (on same computer as server)

Strange, I can't understand well the concept of Threading the Sockets.
I have tried yet I get a NullPointerException from this

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

import java.net.ServerSocket;
import java.net.Socket;

import javax.swing.JTextArea;
import javax.swing.JComboBox;
import javax.swing.DefaultComboBoxModel;

public class Model {

    private int port;
    private int backLog;
    private JTextArea chatArea;
    private JComboBox computers;
    private ServerSocket server;
    private Computer[] connection;

    public Model(int port, int backLog, JTextArea chatArea, JComboBox computers) {
        this.port = port;
        this.backLog = backLog;
        this.chatArea = chatArea;
        this.computers = computers;
        display("Awaiting connections...\n");
    }

    public void runServer() {
        try {
            server = new ServerSocket(port, backLog);

            for(int i=0; i<connection.length; i++) {
                connection[i] = new Computer(server.accept());
                connection[i].run();
            }

        } catch(IOException e) {
            e.printStackTrace();
        }
    }

    public void closeServer() {
        try {
            server.close();
            for(int i=0; i<connection.length; i++) {
                connection[i].close();
            }
        } catch(IOException e) {
            e.printStackTrace();
        }
    }

    private void display(String message) {
            chatArea.append(message);
    }

    private class Computer implements Runnable {

        private Socket socket;
        private ObjectInputStream input;
        private ObjectOutputStream output;
        private String computerName = "";

        public Computer(Socket socket) {
            this.socket = socket;
        }

        public void close() throws IOException {
            socket.close();
            input.close();
            output.close();
        }

        public void run() {
            try {
                getStreams();
            } catch(IOException e) {
                e.printStackTrace();
            }
        }

        private void getStreams() throws IOException {
            output = new ObjectOutputStream(socket.getOutputStream());
            output.flush();
            input = new ObjectInputStream(socket.getInputStream());
            display("Got I/O from " + socket.getInetAddress().getHostName());
        }

        
    }
}

[Norm]

I get a NullPointerException from this

Please copy full text of error message and paste it here.

[chyrl]

Please copy full text of error message and paste it here.

Here's the full message:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at SampleServer.Model.runServer(Model.java:45)
        at SampleServer.Controller.actionPerformed(Controller.java:53)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
        at java.awt.Component.processMouseEvent(Component.java:6099)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
        at java.awt.Component.processEvent(Component.java:5864)
        at java.awt.Container.processEvent(Container.java:2058)
        at java.awt.Component.dispatchEventImpl(Component.java:4466)
        at java.awt.Container.dispatchEventImpl(Container.java:2116)
        at java.awt.Component.dispatchEvent(Component.java:4296)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3986)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)
        at java.awt.Container.dispatchEventImpl(Container.java:2102)
        at java.awt.Window.dispatchEventImpl(Window.java:2454)
        at java.awt.Component.dispatchEvent(Component.java:4296)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:284)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

And Controller: 53 has this line:

model.runServer();

[Norm]

SampleServer.Model.runServer(Model.java:45)

What code is at line 45 in Model? What object at that is null?

Where is private Computer[] connection;
assigned a value? Something like:
connection = new Computer[10]; // create slots for 10 connections

[chyrl]

Ok...
I have included this code in the constructor.

connection = new Computer[backLog];

Now this is strange.
I have configured the problem. Yet my UI freezes when the runServer() is initiated.

[Norm]

Yet my UI freezes when the runServer() is initiated.

Sounds like you are using Swing's EDT (event dispatch thread) to run the code.
You should start your own thread from Swing's thread to allow the EDT to continue servicing the GUI stuff.

To see where the code is "freezing" add some println() statements to show where the code is executing and where it hasn't gotten to yet.

[chyrl]

Strange.
Now I can't solve this problem.
Though the server accepts now new connections.

The GUI still freezes at runServer().
How could I fix it? Can you give me hints?

[Norm]

Is Swing's EDT thread free to run? Is your blocking code on its own thread or on Swing's thread?

[chyrl]

Is Swing's EDT thread free to run? Is your blocking code on its own thread or on Swing's thread?

I can't understand what that EDT means.
But here's my codes on this link.

[JosAH]

I can't understand what that EDT means.
But here's my codes on this link.

Your 'connection' array isn't initialized so it is null.

kind regards,

Jos

[chyrl]

Your 'connection' array isn't initialized so it is null.

kind regards,

Jos

Yes, but when the constructor is called.
It can't be null anymore.

[JosAH]

Yes, but when the constructor is called.
It can't be null anymore.

Why not? Your constructor doesn't initialize that array:

public Model(int port, int backLog, JTextArea chatArea, JComboBox computers) {
        this.port = port;
        this.backLog = backLog;
        this.chatArea = chatArea;
        this.computers = computers;
        display("Awaiting connections...\n");
}

kind regards,

Jos

[chyrl]

Why not? Your constructor doesn't initialize that array:

public Model(int port, int backLog, JTextArea chatArea, JComboBox computers) {
        this.port = port;
        this.backLog = backLog;
        this.chatArea = chatArea;
        this.computers = computers;
        display("Awaiting connections...\n");
}

kind regards,

Jos

Kindly refer now to the update Model.java
Here's the link.