创建具有多个客户端的服务器

Question

I created a Server and Client class. When I run my program it executes perfectly. I am able to communicate between both Server and Client. Now how do I make it to where multiple Clients can be connected to the Server at once? I want to be able to run the Client class and have it program connect to the Server and same port.

This is my Server Class.

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


    public class Server extends JFrame {

     private JTextField enterField;
     private JTextArea displayArea;
     private ObjectOutputStream output;
     private ObjectInputStream input;
     private ServerSocket server;
     private Socket connection;
     private int counter = 1;

       public Server() {
          super("Host Server");

          enterField = new JTextField();
          enterField.setEditable(false);
          enterField.addActionListener(
               new ActionListener() {
                   public void actionPerformed(ActionEvent event) {
                    sendData(event.getActionCommand());
                    enterField.setText("");
                }
            }
        );

    add(enterField, BorderLayout.NORTH);

    displayArea = new JTextArea();
    add(new JScrollPane(displayArea));

     setSize(800,800);
     setVisible(true);
    }

    public void runServer() {
      try {
     server = new ServerSocket(12345, 100);

        while(true) {
            try {
                waitForConnection();
                getStreams();
                processConnection();
            }
            catch (EOFException eofException) {
                displayMessage("\nChat room has close down. Connection Terminated.");
            }
            finally {
                closeConnection();
                ++counter;
            }
        }
    }
    catch (IOException ioException) {
        ioException.printStackTrace();
        }
    }

    private void waitForConnection() throws IOException {
        displayMessage("Waiting for Connection");
        connection = server.accept();
        displayMessage("Connection " + counter + "recieved from: " + 
        connection.getInetAddress().getHostName());
    }

        private void getStreams() throws IOException {
            output = new ObjectOutputStream(connection.getOutputStream());
            output.flush();

            input = new ObjectInputStream(connection.getInputStream());

            displayMessage("\nGot I/O streams\n");
     }

    private void processConnection() throws IOException{
        String message = "Welcome. Chat room has started. \nConnection Successful\n";
        sendData(message);

        setTextFieldEditable(true);

        do {
            try {
                message = (String) input.readObject();
                displayMessage("\n" + message);
            }
            catch (ClassNotFoundException classNotFoundException) {
                displayMessage("\nUnknown object type recieved");
            }
        }while(!message.equals("Client>>>EEEE"));
    }

    private void closeConnection() {
        displayMessage("\nTerminating connection");
        setTextFieldEditable(false);

        try {
            output.close();
            input.close();
            connection.close();
        }
        catch (IOException ioException) {
            ioException.printStackTrace();
        }
    }

    private void sendData(String message) {
        try {
            output.writeObject("Server>>>" + message);
            output.flush();
            displayMessage("\nServer>>> " + message);
        }
        catch (IOException ioException) {
            displayArea.append("\nError writing object");
        }
    }

    private void displayMessage(final String messageToDisplay) {
        SwingUtilities.invokeLater(
                new Runnable() {
                    public void run() {
                        displayArea.append(messageToDisplay);
                    }
                }
        );
    }

    private void setTextFieldEditable(final boolean editable) {
        SwingUtilities.invokeLater(
                new Runnable() {
                    public void run() {
                        enterField.setEditable(editable);
                    }
                }
        );
     }
    public static void main(String[] args) {
        Server application = new Server();
        application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        application.runServer();
    }


}

...

This is my Client Class.

   import java.io.*;
   import javax.swing.*;
   import java.awt.event.*;
   import java.net.*;
   import java.awt.*;
      public class Client extends JFrame{
         private JTextField enterField;
         private JTextArea displayArea;
         private ObjectOutputStream output;
         private ObjectInputStream input;
         private String message = "";
         private String chatServer;
         private Socket client;

     public Client(String host) {
        super("Client");

        chatServer = host;

        enterField = new JTextField();
        enterField.setEditable(false);
        enterField.addActionListener(
                new ActionListener() {
                    public void actionPerformed(ActionEvent event) {
                        sendData(event.getActionCommand());
                        enterField.setText("");
                     }
                }
            );
        add(enterField, BorderLayout.NORTH);

        displayArea = new JTextArea();
        add(new JScrollPane(displayArea), BorderLayout.CENTER);

        setSize(800,800);
        setVisible(true);
    }

    public void runClient() {

        try {
            connectToServer();
            getStreams();
            processConnection();
        }
        catch (EOFException iofException) {
            displayMessage("\nClient terminated connection");
        }
        catch (IOException ioException) {
            ioException.printStackTrace();
        }
        finally {
            closeConnection();
        }
    }

    private void connectToServer() throws IOException {

        displayMessage("Attempting connection\n");

        client = new Socket(InetAddress.getByName(chatServer), 12345);

        displayMessage("Connected to: " + client.getInetAddress().getHostName());
    }

    private void getStreams() throws IOException {

        output = new ObjectOutputStream(client.getOutputStream());
        output.flush();

        input = new ObjectInputStream(client.getInputStream());


    }

    private void processConnection() throws IOException {

        setTextFieldEditable(true);

        do {
            try {
                message = (String) input.readObject();
                displayMessage("\n" + message);
            }
            catch (ClassNotFoundException classNotFoundException) {
                displayMessage("\nErro with recieving chat message");
            }
        } while (!message.equals("SERVER>>>TERMINATE"));
    }

    private void closeConnection() {
         displayMessage("\nClosing connection");
         displayMessage("\nAll users have left the chat");

         setTextFieldEditable(false);

        try {
            output.close();
            input.close();
            client.close();
        }
        catch (IOException ioException) {
            ioException.printStackTrace();
        }
    }

    private void sendData(String message) {
        try {
            output.writeObject("CLIENT>>> " + message);
            output.flush();
            displayMessage("\nCLIENT>>> " + message);
        }
        catch (IOException ioException) {
            displayArea.append("\nError writing object");
       }
    } 

   `private void displayMessage(final String messageToDisplay) {
        SwingUtilities.invokeLater(
               new Runnable() {
                    public void run() {
                        displayArea.append(messageToDisplay);
                    }
                }
            );
    }

    private void setTextFieldEditable(final boolean editable) {
        SwingUtilities.invokeLater(
                new Runnable() {
                    public void run() {
                        enterField.setEditable(editable);
                    }
                }
            );
    }

    public static void main(String[] args) {
        Client application;

        if(args.length == 0)
            application = new Client("127.0.0.1");
        else
            application = new Client(args[0]);

        application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        application.runClient();
    }
}

...

Answer 1

Your current implementation of Server handles only one connection from client.

To handle multiple connections, you need to implement some ClientHandler class responsible for reading from and writing to the client's socket which should run in its own thread:

class ConnectionHandler implements Runnable {
    private final Socket socket;
    private final Server server;

    public ConnectionHandler(Socket socket, Server server) {
        this.socket = socket;
        this.server = server;
    }

    @Override
    public void run() {
        // implement I/O with client, if client logs out or connection lost, you notify server
    }
}

Then you need to modify your Server code to support multiple clients, for example:

    List<ConnectionHandler> clients = new ArrayList<>();

    private void waitForConnection() throws IOException {
        displayMessage("Waiting for Connection");
        Socket socket = server.accept();
        ConnectionHandler clientHandler = new ConnectionHandler(socket, this);
        clients.add(clientHandler);
        Thread handlerThread = new Thread(clientHandler);
        handlerThread.start();

        displayMessage("Connection #" + clients.size() + "received from: " + 
        socket.getInetAddress().getHostName());
    }