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TCPConnectionListener.java
package ru.example.network;

import java.io.IOException;

public interface TCPConnectionListener {

    void onConnectionReady(TCPConnection tcpConnection);

    void onReceiveString(TCPConnection tcpConnection, String s);

    void onDisconnect(TCPConnection tcpConnection);

    void onException(TCPConnection tcpConnection, IOException e);

}
¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬TCPConnection.java
package ru.example.network;

import java.io.*;
import java.net.Socket;
import java.nio.charset.Charset;

/**
 * Класс представляет TCP-соединение
 */
public class TCPConnection {
    private final Socket socket;
    private final Thread thread;
    private final TCPConnectionListener eventListener;
    private final BufferedReader in;
    private final BufferedWriter out;

    public TCPConnection(TCPConnectionListener eventListener, String ipAddress, int port) throws IOException {
        this(eventListener, new Socket(ipAddress, port));
    }

    public TCPConnection(TCPConnectionListener eventListener, Socket socket) throws IOException {
        this.eventListener = eventListener;
        this.socket = socket;
        in = new BufferedReader(new InputStreamReader(socket.getInputStream(), Charset.forName("UTF-8")));
        out = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream(), Charset.forName("UTF-8")));
        thread = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    eventListener.onConnectionReady(TCPConnection.this);
                    while (!thread.isInterrupted()) {
                        eventListener.onReceiveString(TCPConnection.this, in.readLine());
                    }
                } catch (IOException e) {
                    eventListener.onException(TCPConnection.this, e);
                } finally {
                    eventListener.onDisconnect(TCPConnection.this);
                }
            }
        });
        thread.start();
    }

    public synchronized void sendString(String value) {
        try {
            out.write(value + "\r\n");
            out.flush();
        } catch (IOException e) {
            eventListener.onException(this, e);
            disconnect();
        }
    }

    private synchronized void disconnect() {
        thread.interrupt();
        try {
            socket.close();
        } catch (IOException e) {
            eventListener.onException(this, e);
        }
    }

    @Override
    public String toString() {
        return "TCPConnection: " + socket.getInetAddress() + ": " + socket.getPort();
    }
}
ChatServer.java
package ru.example.chat.server;

import ru.example.network.TCPConnection;
import ru.example.network.TCPConnectionListener;

import java.io.IOException;
import java.net.ServerSocket;
import java.util.ArrayList;

@SuppressWarnings("InfiniteLoopStatement")
public class ChatServer implements TCPConnectionListener {
    public static void main(String[] args) {
        new ChatServer();
    }

    private final ArrayList<TCPConnection> connections = new ArrayList<>();

    private ChatServer() {
        System.out.println("Server running...");
        try(ServerSocket serverSocket = new ServerSocket(8189)) {
            while(true) {
                try {
                    new TCPConnection(this, serverSocket.accept());
                } catch (IOException e) {
                    System.out.println("TCPConnection exception: " + e);
                }
            }
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }


    @Override
    public synchronized void onConnectionReady(TCPConnection tcpConnection) {
        connections.add(tcpConnection);
        sendToAllConnections("Client connected: " + tcpConnection);
    }

    @Override
    public synchronized void onReceiveString(TCPConnection tcpConnection, String value) {
        sendToAllConnections(value);
    }

    @Override
    public synchronized void onDisconnect(TCPConnection tcpConnection) {
        connections.remove(tcpConnection);
        sendToAllConnections("Client disconnected: " + tcpConnection);
    }

    @Override
    public void onException(TCPConnection tcpConnection, IOException e) {
        System.out.println("TCPConnection exception: " + e);
    }

    private void sendToAllConnections(String value){
        System.out.println(value);
        for (TCPConnection connection : connections) {
            connection.sendString(value);
        }
    }
}
ClientWindow.java
package ru.example.chat.client;

import ru.example.network.TCPConnection;
import ru.example.network.TCPConnectionListener;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;

public class ClientWindow extends JFrame implements ActionListener, TCPConnectionListener {

    private static final String IP_ADDR = "10.254.10.145";
    private static final int PORT = 8189;
    private static final int WIDTH = 600;
    private static final int HEIGHT = 400;

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new ClientWindow();
            }
        });
    }

    private final JTextArea log = new JTextArea();
    private final JTextField fieldNickname = new JTextField("Гость");
    private final JTextField fieldInput = new JTextField();

    private TCPConnection connection;

    private ClientWindow() {
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setSize(WIDTH, HEIGHT);
        setLocationRelativeTo(null);
        setAlwaysOnTop(true);

        add(fieldNickname, BorderLayout.NORTH);

        log.setEditable(false);
        log.setLineWrap(true);
        add(new JScrollPane(log), BorderLayout.CENTER);

        fieldInput.addActionListener(this);
        add(fieldInput, BorderLayout.SOUTH);

        setVisible(true);
        try {
            connection = new TCPConnection(this, IP_ADDR, PORT);
        } catch (IOException e) {
            printMessage("Connection exception: " + e);
        }
    }


    @Override
    public void actionPerformed(ActionEvent e) {
        String msg = fieldInput.getText();
        if (msg.equals("")) return;
        fieldInput.setText(null);
        connection.sendString(fieldNickname.getText() + ": " + msg);
    }


    @Override
    public void onConnectionReady(TCPConnection tcpConnection) {
        printMessage("Connection ready...");
    }

    @Override
    public void onReceiveString(TCPConnection tcpConnection, String value) {
        printMessage(value);
    }

    @Override
    public void onDisconnect(TCPConnection tcpConnection) {
        printMessage("Connection close");
    }

    @Override
    public void onException(TCPConnection tcpConnection, IOException e) {
        printMessage("Connection exception: " + e);
    }

    private synchronized void printMessage(String message) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                log.append(message + "\n");
            }
        });
    }
}