Hello,

In the following programs, I am trying to add multiple clients. The Client program remains unchanged. For the Server program, I am using a thread (custom class implements the Runnable interface) to open a new socket and process every client request. My questions follow the programs.

ChatServer.java:

    import java.net.*;
    import java.io.*;
    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;

    public class ChatServer  implements Runnable
    {

     private Socket socket = null;
     private ServerSocket    server   = null;
     private Thread thread;
     private int ID = 1;

     public ChatServer(int port)
     {

        try
        {
           System.out.println("Binding to port " + port + ", please wait  ...");
           server = new ServerSocket(port);

       }

       catch(IOException ioe)
        {  System.out.println(ioe);

        }


        thread = new Thread (this);
        thread.start();

     }


     public void run ()
     {
          System.out.println("Server started: " + server);
          System.out.println("Waiting for a client ...");
          boolean flag = true;

          while (flag == true)
          {
              try
               {
                  System.out.println ("I am here");
                  ServerThread st = new ServerThread (server.accept());
                  System.out.println("Client#" + ID + " accepted ");
                  st.open();
                  st.start();
                  ID++;

               }
              catch (IOException e)
              {}
         }


     }


     public static void main(String args[])
     {
         ChatServer server = new ChatServer(2000);
     }




     class ServerThread extends JFrame implements Runnable
       {
         private BufferedReader  reader =  null;
         private PrintWriter     writer = null;
         private BufferedReader  console   = null;

         private JTextField field;
         private JTextArea area;
         private JButton button;
         private JScrollPane pane;
         private Socket  socket   = null;

         public ServerThread (Socket s)
         {
            super("Server");
            socket = s;

            setLayout (new FlowLayout());

            field = new JTextField (20);
            area = new JTextArea (20, 20);
            button = new JButton ("Send to Client");
            area.setLineWrap(true);
            pane = new JScrollPane(area);

            add(area);
            add(field);
            add (button);

            addWindowListener(

               new WindowAdapter ()
               {
                   public void windowClosing (WindowEvent e)
                   {
                       System.exit(0);
                   }
               }
             );

            button.addActionListener (

               new ActionListener()
               {
                   public void actionPerformed (ActionEvent event)
                   {
                       writer.println (field.getText());
                       area.append ("SERVER :   " + field.getText());
                       field.setText("");
                   }
               }
           );

            setSize (500, 500);
            setVisible (true);

           }

           public void run()
           {

             boolean flag = true;

             while (flag == true)
             {
                 try
                    {
                        String line = reader.readLine();
                        area.append ("CLIENT :  " + line + "\n");
                    }
                 catch (Exception e)
                 {}
             }



           }

          public void open() throws IOException
          {
            reader = new BufferedReader (new InputStreamReader (socket.getInputStream()));
            console   = new BufferedReader(new InputStreamReader(System.in));
            writer  = new PrintWriter (socket.getOutputStream(), true);
          }

       }

    }

ChatClient.java

import java.net.*;
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ChatClient extends JFrame implements Runnable
{
 private Socket             socket    = null;
 private BufferedReader     console   = null;
 private BufferedReader     reader    =  null;
 private PrintWriter        writer    = null;
 private Thread thread;
 private JTextField field;
 private JTextArea area;
 private JButton button;
 private JScrollPane pane;


 public ChatClient(String serverName, int serverPort)
 {
    super("Client");

    setLayout (new FlowLayout());

    field = new JTextField (20);
    area = new JTextArea (20, 20);
    button = new JButton ("Send to Server");
    area.setLineWrap(true);
    pane = new JScrollPane(area);

    add(area);
    add(field);
    add (button);

    addWindowListener(

       new WindowAdapter ()
       {
           public void windowClosing (WindowEvent e)
           {
               System.exit(0);
           }
       }
     );

    button.addActionListener (

       new ActionListener()
       {
           public void actionPerformed (ActionEvent event)
           {
               writer.println (field.getText());
               area.append ("CLIENT :   " + field.getText() +"\n");
               field.setText("");
           }
       }
   );


    System.out.println("Establishing connection. Please wait ...");
    try
    {  socket = new Socket(serverName, serverPort);
       System.out.println("Connected: " + socket);
       start();
    }
    catch(UnknownHostException uhe)
    {  System.out.println("Host unknown: ");
    }
    catch(IOException ioe)
    {  System.out.println("Unexpected exception: ");
    }




    thread = new Thread (this);
    thread.start();

    setSize (500, 500);
    setVisible (true);

 }

 public void run ()
 {
     boolean flag = true;

     while (flag == true)
     {
         try
            {
                String line = reader.readLine();
                area.append ("SERVER :  " + line + "\n");
            }
         catch (Exception e)
         {}
     }

 }



 public void start() throws IOException
 {
   reader = new BufferedReader (new InputStreamReader (socket.getInputStream()));
    console   = new BufferedReader(new InputStreamReader(System.in));
    writer  = new PrintWriter (socket.getOutputStream(), true);
 }


 public static void main(String args[])
 {
   ChatClient client = new ChatClient("localhost", 2000);
 }
}

-----------------------------------------------------------------

Questions:

a) In ChatServer.java, I get a syntax error when I try to start the thread that is implemented by the ServerThread class using the start method (to call run()):

      while (flag == true)
      {
          try
           {
              System.out.println ("I am here");
              ServerThread st = new ServerThread (server.accept());
              System.out.println("Client#" + ID + " accepted ");
              st.open();
              st.start(); //error on this line
              ID++;

           }
          catch (IOException e)
          {}
       }

What I am doing wrong here?

b) The major issue I am having is that when I start the second client, the console of the Server goes blank and it does not show the line, "Client#2 accepted". In this state, only communication between the Server and the first Client works. The second Client is not able to communicate at all. I would be grateful for any help/advise.

Thank you!!

Edited 4 Years Ago by javaprog200

I get a syntax error

Please post the full text of the compiler's error message.

Please explain what "console" goes blank? Is that the OS's command console or what?

Edited 4 Years Ago by NormR1

I am using BlueJ.

a) The syntax error is, "cannot find symbol - method start()"

b) By console, I mean the application window of BlueJ that opens when a program uses 'System.out.println(".....") to print a line.

Where is the start() method defined? The compiler can not find it in the ServerThread class.

Sorry, I have no idea of how BlueJ works.

Try executing the class in the OS's command prompt window to see if it is different.

Edited 4 Years Ago by NormR1

public void start() throws IOException
{
reader = new BufferedReader (new InputStreamReader (socket.getInputStream()));
console = new BufferedReader(new InputStreamReader(System.in));
writer = new PrintWriter (socket.getOutputStream(), true);
}
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