Developing a Realtime Chat System

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

public class ChatServer {
    private static final int PORT = 12345;
    private static final Set<ClientHandler> CLIENTS = Collections.synchronizedSet(new HashSet<>());

    public static void main(String[] args) {
        System.out.println("Chat server started...");

        try (ServerSocket serverSocket = new ServerSocket(PORT)) {
            while (true) {
                Socket clientSocket = serverSocket.accept();
                System.out.println("New client connected: " + clientSocket.getInetAddress());

                ClientHandler clientHandler = new ClientHandler(clientSocket);
                CLIENTS.add(clientHandler);
                new Thread(clientHandler).start();
            }
        } catch (IOException e) {
            System.out.println("Server error: " + e.getMessage());
        }
    }

    public static void boardcast(String message, ClientHandler sender) {
        synchronized (CLIENTS) {
            for (ClientHandler client : CLIENTS) {
                if (client != sender) {
                    client.sendMessage(message);
                }
            }
        }
    }

    public static void removeClient(ClientHandler clientHandler) {
        CLIENTS.remove(clientHandler);
    }
}

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

public class ChatClient {
    private static final String SERVER_ADDRESS = "127.0.0.1";
    private static final int SERVER_PORT = 12345;

    public static void main(String[] args) {
        try (Socket socket = new Socket(SERVER_ADDRESS, SERVER_PORT)) {
            BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
            BufferedReader console = new BufferedReader(new InputStreamReader(System.in));

            System.out.println("Connected to chat server.");

            new Thread(() -> {
                String message;
                try {
                    while ((message = in.readLine()) != null) {
                        System.out.println("Received: " + message);
                    }
                } catch (IOException e) {
                    System.out.println("Connection error" + e.getMessage());
                }
            }).start();

            String userInput;
            while ((userInput = console.readLine()) != null) {
                out.println(userInput);
            }
        } catch (IOException e) {
            System.out.println("Client error: " + e.getMessage());
        }
    }
}

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

public class ClientHandler implements Runnable {
    private final Socket clientSocket;
    private PrintWriter out;

    public ClientHandler(Socket clientSocket) {
        this.clientSocket = clientSocket;
    }

    @Override
    public void run() {
        try (BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()))) {
            out = new PrintWriter(clientSocket.getOutputStream(), true);
            String message;
            while ((message = in.readLine()) != null) {
                System.out.println("Received: " + message);
                ChatServer.boardcast(message, this);
            }
        } catch (IOException e) {
            System.out.println("Client Error: " + e.getMessage());
        } finally {
            ChatServer.removeClient(this);
            try {
                clientSocket.close();
            } catch (IOException e) {
                System.out.println("Failed to close socket: " + e.getMessage());
            }
        }
    }

    public void sendMessage(String message) {
        if (out != null) {
            out.println(message);
        }
    }
}