Stage #4: Group chat with named users

src/chat/clientside/Client.java

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+package chat.clientside;
+
+import chat.common.Commands;
+import chat.common.Configs;
+
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.net.InetAddress;
+import java.net.Socket;
+import java.time.LocalDateTime;
+import java.util.Scanner;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+public class Client {
+    private static final Logger LOGGER = Logger.getLogger(Client.class.getName());
+
+    private final String name;
+
+    public Client(String name) {
+        this.name = name;
+    }
+
+    public void start() {
+        final Scanner scanner = new Scanner(System.in);
+
+        try (final Socket socket = new Socket(InetAddress.getByName(Configs.CHAT_SERVER_ADDRESS), Configs.CHAT_SERVER_PORT)) {
+            LOGGER.info(String.format("Established connection to %s", socket.getRemoteSocketAddress().toString()));
+
+            final DataOutputStream output = new DataOutputStream(socket.getOutputStream());
+            final DataInputStream input = new DataInputStream(socket.getInputStream());
+
+            final Thread receivedMessagesHandler = new Thread(() -> {
+                try {
+                    while (true) {
+                        final String msg = input.readUTF();
+                        final LocalDateTime now = LocalDateTime.now().withNano(0);
+                        System.out.println(String.format("[%s] %s", now.toString().replace('T', ' '), msg));
+                    }
+                } catch(IOException e){
+                    LOGGER.log(Level.SEVERE, "Cannot interact with the server");
+                }
+            });
+
+            receivedMessagesHandler.start();
+
+            output.writeUTF(name);
+
+            while (true) {
+                final String msgToSend = scanner.nextLine();
+                output.writeUTF(msgToSend);
+
+                if (msgToSend.trim().equalsIgnoreCase(Commands.EXIT.getCode())) {
+                    break;
+                }
+            }
+
+            socket.close();
+            input.close();
+            output.close();
+        } catch (Exception e) {
+            LOGGER.log(Level.SEVERE, "Cannot interact with the server", e);
+        }
+    }
+
+    public static void main(String[] args) {
+        if (args.length < 1) {
+            System.out.println("Please, specify your name as an argument when starting it.");
+            return;
+        }
+
+        Client client = new Client(args[0]);
+        client.start();
+    }
+}

src/chat/common/Commands.java

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+package chat.common;
+
+public enum Commands {
+
+    EXIT("/exit"), LIST("/list");
+
+    Commands(String code) {
+        this.code = code;
+    }
+
+    private final String code;
+
+    public String getCode() {
+        return code;
+    }
+}

src/chat/common/Configs.java

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+package chat.common;
+
+public final class Configs {
+
+    private Configs() { }
+
+    public static final int CHAT_SERVER_PORT = 23456;
+    public static final String CHAT_SERVER_ADDRESS = "127.0.0.1";
+    public static final int THREAD_POOL_SIZE = 1;
+}

src/chat/serverside/ClientHandler.java

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+package chat.serverside;
+
+import chat.common.Commands;
+
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.net.Socket;
+import java.util.UUID;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+public class ClientHandler extends Thread {
+    private static final Logger LOGGER = Logger.getLogger(ClientHandler.class.getName());
+
+    private final Server server;
+    private final Socket clientSocket;
+
+    private final DataInputStream input;
+    private final DataOutputStream output;
+
+    private final UUID clientId;
+    private String clientName = "Unknown";
+
+    public ClientHandler(UUID clientId, Server server, Socket client) throws IOException {
+        this.clientId = clientId;
+        this.server = server;
+        this.clientSocket = client;
+        this.input = new DataInputStream(client.getInputStream());
+        this.output = new DataOutputStream(client.getOutputStream());
+    }
+
+    public void sendMsg(String msg) throws IOException {
+        output.writeUTF(msg);
+        output.flush();
+    }
+
+    @Override
+    public void run() {
+        try {
+            this.clientName = input.readUTF();
+
+            final String helloMsg = String.format("%s is ready to start chatting\n", clientName);
+            server.broadcastMessage(helloMsg);
+
+            while (true) {
+                if (clientSocket.isClosed()) {
+                    break;
+                }
+
+                final String msg = input.readUTF();
+                if (msg.trim().equalsIgnoreCase(Commands.EXIT.getCode())) {
+                    disconnect();
+                    break;
+                }
+
+                final String msgWithClient = clientName + ": " + msg;
+                LOGGER.info(msgWithClient);
+                server.broadcastMessage(msgWithClient);
+            }
+        } catch(IOException e){
+            LOGGER.log(Level.SEVERE, String.format("Cannot interact with %s", clientName), e);
+            disconnect();
+        }
+    }
+
+    private void disconnect() {
+        try {
+            clientSocket.close();
+            input.close();
+            output.close();
+        } catch (IOException e) {
+            LOGGER.log(Level.SEVERE, String.format("Cannot disconnect %s", clientName), e);
+        }
+        server.dropClient(clientId);
+        server.broadcastMessage(String.format("%s disconnected from the server\n", clientName));
+    }
+
+    public String getClientName() {
+        return clientName;
+    }
+
+    public UUID getClientId() {
+        return clientId;
+    }
+}

src/chat/serverside/Server.java

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+package chat.serverside;
+
+import chat.common.Configs;
+
+import java.io.IOException;
+import java.net.ServerSocket;
+import java.net.Socket;
+import java.util.ArrayList;
+import java.util.Objects;
+import java.util.UUID;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+public class Server {
+    private static final Logger LOGGER = Logger.getLogger(Server.class.getName());
+
+    private static ArrayList<ClientHandler> handlers = new ArrayList<>();
+
+    private final int port;
+
+    public Server(int port) {
+        this.port = port;
+    }
+
+    public void start() {
+        try (final ServerSocket server = new ServerSocket(port)) {
+            LOGGER.info(String.format("The chat server has been started on port %d", server.getLocalPort()));
+            while (true) {
+                LOGGER.info("Waiting for a client");
+                final Socket client = server.accept();
+                regNewClient(client);
+            }
+        } catch (IOException e) {
+            LOGGER.log(Level.SEVERE, String.format("Cannot start server on %d", Configs.CHAT_SERVER_PORT), e);
+        }
+    }
+
+    public synchronized void regNewClient(Socket client) {
+        try {
+            final ClientHandler clientThread = new ClientHandler(UUID.randomUUID(), this, client);
+            clientThread.start();
+            handlers.add(clientThread);
+        } catch (IOException e) {
+            LOGGER.log(Level.SEVERE, "Cannot register a new client", e);
+        }
+    }
+
+    public synchronized void dropClient(UUID clientId) {
+        handlers.removeIf(client -> Objects.equals(client.getClientId(), clientId));
+    }
+
+    public synchronized void broadcastMessage(String msg) {
+        handlers.forEach(handler -> {
+            try {
+                handler.sendMsg(msg);
+            } catch (IOException e) {
+                LOGGER.log(Level.SEVERE, String.format("Cannot send message to %s", handler.getClientName()), e);
+            }
+        });
+    }
+
+    public static void main(String[] args) {
+        final Server chatServer = new Server(Configs.CHAT_SERVER_PORT);
+        chatServer.start();
+    }
+}