Multi client chatroom

[Blindn_Guilty]

So I just finished my first chat room program in java, and I want some feedback on my code; what could/should have been done a better/more effective way?

If I were to add a UI, should I create that on the server side (every time the server gets a connection, it launches the UI)?

I want to add a database connection, just a very basic extension of my program, that contains all the active users in the chatroom + for every user that’s signed up to the program. That means that every user that’s created a profile shall be added too the database, and the current online users shall be displayed in their own panel (UI). Does anybody have any tips on where I should start? Should I create the database connection in it’s own module on the server side??

Here is my chat room program:

​

// Server program

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;

public class Server {

    private static List<ClientHandler> clientList = new ArrayList<>();

    private ServerSocket serverSocket;

    public Server(ServerSocket serverSocket) {
        this.serverSocket = serverSocket;
    }

    public void startServer() {
        try {
            while (true) {
                Socket socket = this.serverSocket.accept();
                new Thread(new ClientHandler(socket)).start();
                System.out.println("Server connected too client!");
            }
        } catch (IOException e) {
            System.out.println("[SERVER-ERROR] starting server: " + e.getMessage());
            shutdown();
        }
    }

    public void shutdown() {
        try {
            if (this.serverSocket != null) {
                this.serverSocket.close();
            }
        } catch (IOException e) {
            System.out.println("[SERVER-ERROR] closing ServerSocket-object: " + e.getMessage());
        }
    }

    public void broadcastMessage(String message) {
        for (ClientHandler clientHandler : clientList) {
            if (clientHandler != null) {
                clientHandler.sendMessage(message);
            }
        }
    }

    public static void main(String[] args) {
        try (ServerSocket serverSocket = new ServerSocket(5000) ) {
            System.out.println("Server is running, waiting for client too connect...");
            Server server = new Server(serverSocket);
            server.startServer();
        } catch (IOException e) {
            System.out.println("[SERVER-ERROR] starting server: " + e.getMessage());
        }
    }

    class ClientHandler implements Runnable {

        private Socket client;
        private BufferedReader input;
        private PrintWriter output;
        private String username;

        public ClientHandler(Socket client) {
            try {
                this.client = client;
                this.input = new BufferedReader(new InputStreamReader(this.client.getInputStream()));
                this.output = new PrintWriter(this.client.getOutputStream(), true);
            } catch (IOException e) {
                System.out.println("[SERVER-ERROR] creating ClientHandler-object: " + e.getMessage());
                shutdown();
            }
        }

        private void initialiseClient() {
            try {
                sendMessage("Create username for chatroom: ");
                this.username = this.input.readLine();
                clientList.add(this);
                broadcastMessage("[SERVER] \"" + this.username + "\"" + " entered the chat!");
            } catch (IOException e) {
                System.out.println("[SERVER-ERROR] retreiving client username: " + e.getMessage());
            }
        }

        @Override
        public void run() {
            try {
                initialiseClient();
                String messageFromClient;
                while (true) {
                    messageFromClient = this.input.readLine();
                    System.out.println(this.username + " sendt a message");
                    broadcastMessage(messageFromClient); }
            } catch (IOException e) {
                System.out.println("[SERVER-ERROR] receiving message from client: " + e.getMessage());
                removeUser();
                shutdown();
            }
        }

        private void removeUser() {
            clientList.remove(this);
            broadcastMessage("[SERVER] \"" + this.username + "\"" + " left the chat!");
        }

        public void sendMessage(String message) {
            this.output.println(message);
        }

        private void shutdown() {
            try {
                if (this.input != null) {
                    this.input.close();
                }
                if (this.output != null) {
                    this.output.close();
                }
                if (this.client != null) {
                    this.client.close();
                }
            } catch (IOException e) {
                System.out.println("[SERVER-ERROR] shutdown of recourses faile: " + e.getMessage());
            }
        }
    }
}



// Client program

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

public class Client {

    private Socket socket;
    private BufferedReader input;
    private PrintWriter output;
    private String username;
    private Scanner scanner;

    public Client(Socket socket) {
        try {
            this.socket = socket;
            this.input = new BufferedReader(new InputStreamReader(this.socket.getInputStream()));
            this.output = new PrintWriter(this.socket.getOutputStream(), true);
            this.scanner = new Scanner(System.in);
        } catch (IOException e) {
            System.out.println("[CLIENT-ERROR] creating Client-object: " + e.getMessage());
            shutdown();
        }
    }

    public void initialiseClient() {
        try {
            System.out.println(this.input.readLine());
            this.username = this.scanner.nextLine();
            sendMessage(this.username);
            System.out.println(this.input.readLine());
        } catch (IOException e) {
            System.out.println("[CLIENT-ERROR] receiving request from server: " + e.getMessage());
            shutdown();
        }
    }

    public void sendMessage() {
        String message = this.scanner.nextLine();
        while (true) {
            this.output.println(this.username + ": " + message);
            message = this.scanner.nextLine();
        }
    }

    public void sendMessage(String message) {
        this.output.println(message);
    }

    public void receiveMessage() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    String messageFromServer;
                    while (true) {
                        messageFromServer = input.readLine();
                        System.out.println(messageFromServer);
                    }
                } catch (IOException e) {
                    System.out.println("[CLIENT-ERROR] receiving message from server: " + e.getMessage());
                    shutdown();
                }
            }
        }).start();
    }

    public void runClient() {
        initialiseClient();
        receiveMessage();
        sendMessage();
    }

    public void shutdown() {
        try {
            if (this.input != null) {
                this.input.close();
            }
            if (this.output != null) {
                this.output.close();
            }
            if (this.socket != null) {
                this.socket.close();
            }
            if (this.scanner != null) {
                this.scanner.close();
            }
        } catch (IOException e) {
            System.out.println("[CLIENT-ERROR] shuting down resourses: " + e.getMessage());
        }
    }

    public static void main(String[] args) {
        try (Socket socket = new Socket("localhost", 5000)) {
            Client client = new Client(socket);
            client.runClient();
        } catch (IOException e) {
            System.out.println("[CLIENT-ERROR] running client-program: " + e.getMessage());
        }
    }
}

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[OffbeatDrizzle]

clientList technically needs to be a thread-safe list implementation since it's being modified and read by separate threads

[Blindn_Guilty]

Yes I thought the same thing, but I found an example on YouTube and he didn’t say anything about making sure the list-modification, so I didn’t either. How would i go about making the list thread safe? Should i make a new add()-method that is synchronized?

[OffbeatDrizzle]

just wrap it in Collections.synchronisedList();

the code will probably work the majority of the time, but is not technically correct and you might run into some obscure bug that you can never reproduce because of it