ClientHandler.java

import java.io.*;
import java.net.Socket;
import java.util.ArrayList;

public class ClientHandler implements Runnable {

    // List of all handlers
    public static ArrayList<ClientHandler> clientHandlers = new ArrayList<>();

    private Socket socket;
    private BufferedReader bufferedReader;
    private BufferedWriter bufferedWriter;
    private String clientUsername;

    public ClientHandler(Socket socket) {
        try {
            this.socket = socket;
            this.bufferedWriter = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
            this.bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));

            this.clientUsername = bufferedReader.readLine();

            clientHandlers.add(this);

            // 1. Announce the new user
            broadcastMessage("SERVER: " + clientUsername + " has entered the chat!");

            // 2. SEND THE UPDATED USER LIST TO EVERYONE
            broadcastUserList();

        } catch (IOException e) {
            closeEverything(socket, bufferedReader, bufferedWriter);
        }
    }

    @Override
    public void run() {
        String messageFromClient;
        while (socket.isConnected()) {
            try {
                messageFromClient = bufferedReader.readLine();
                broadcastMessage(messageFromClient);
            } catch (IOException e) {
                closeEverything(socket, bufferedReader, bufferedWriter);
                break;
            }
        }
    }

    public void broadcastMessage(String messageToSend) {
        for (ClientHandler clientHandler : clientHandlers) {
            try {
                if (!clientHandler.clientUsername.equals(clientUsername)) {
                    clientHandler.bufferedWriter.write(messageToSend);
                    clientHandler.bufferedWriter.newLine();
                    clientHandler.bufferedWriter.flush();
                }
            } catch (IOException e) {
                closeEverything(socket, bufferedReader, bufferedWriter);
            }
        }
    }

    // --- NEW METHOD: Broadcasts the list of names ---
    public void broadcastUserList() {
        // Build a string like "USERS:Alice,Bob,Charlie"
        StringBuilder names = new StringBuilder("USERS:");
        for (ClientHandler handler : clientHandlers) {
            names.append(handler.clientUsername).append(",");
        }

        // Send this special string to EVERYONE (including myself)
        for (ClientHandler handler : clientHandlers) {
            try {
                handler.bufferedWriter.write(names.toString());
                handler.bufferedWriter.newLine();
                handler.bufferedWriter.flush();
            } catch (IOException e) {
                closeEverything(socket, bufferedReader, bufferedWriter);
            }
        }
    }

    public void removeClientHandler() {
        clientHandlers.remove(this);
        broadcastMessage("SERVER: " + clientUsername + " has left the chat.");
        broadcastUserList(); // Update the list when someone leaves!
    }

    public void closeEverything(Socket socket, BufferedReader bufferedReader, BufferedWriter bufferedWriter) {
        removeClientHandler();
        try {
            if (bufferedReader != null) bufferedReader.close();
            if (bufferedWriter != null) bufferedWriter.close();
            if (socket != null) socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}