What's causing java.net.SocketException: Connection reset after closing client?

Question

I'm writing a server/client application for school.

Every time I close the client, the server throws 'java.net.SocketException: Connection reset'. I think, I have to close the socket in the client before closing the JavaFX-window, but where? Or what do you think?

I've seen a similar question, but I don't know how to implement it correctly in my programm.

Exception:

20:05:27.132 [Thread-2] ERROR OnlineBank - java.net.BindException: Address already in use: JVM_Bind
19:51:06.580 [Thread-1] ERROR ServerHandler - java.net.SocketException: Connection reset
19:51:06.580 [Thread-2] ERROR ServerHandler - java.net.SocketException: Connection reset

MyProgramm:

private MyProgramm() {      
    server = new MyServer(Constants.REMOTE_PORT);
    try 
        server.start();
    } catch (ClassNotFoundException | IOException e) {
        logger.error(e);    
    }
}

MyServer:

public void start() throws ClassNotFoundException, IOException {
        try {
            serverSocket = new ServerSocket(this.port);

            while (true) {
                Socket client = serverSocket.accept();
                logger.debug(getClass().getName() + " accepts");

                Thread threadHandler = new Thread(new ServerHandler(client));
                threadHandler.start();
            }

        } finally {
            if (serverSocket != null) {
                serverSocket.close();
            }
        }

    }

ServerHandler:

@Override
    public void run() {

        try (InputStream in = clientSocket.getInputStream();
                OutputStream out = clientSocket.getOutputStream();
                ObjectInputStream oin = new ObjectInputStream(in);
                ObjectOutputStream oos = new ObjectOutputStream(out)) {

            while (true) {
                try {
                    Object receivedObject = oin.readObject();
                    handleReceivedObject(oos, receivedObject);

                } catch (ClassNotFoundException e) {
                    logger.error(e);
                    break;
                }
            }
        } catch (IOException e) {
            logger.error(e);
        }
    }

MainClient:

public class MainClient extends Application {
    private static Client client;

    public static void main(String[] args) {
        launch(args);
        try {
            client = new Client();
        } catch (IOException e) {
            logger.error(e);
        }
    }

    @Override
    public void start(Stage primaryStage) throws Exception {
        Parent root = FXMLLoader.load(getClass().getResource("/welcome.fxml"));
        Scene scene = new Scene(root);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    @Override
    public void stop() throws Exception {
        super.stop();

        // to avoid NullPointerException
        if (Client != null && Client.getSocket() != null) {
            Client.getSocket().close();
        }
    }
}

Client:

public class Client {

    private Socket socket;
    public Client(String remoteHost, int port) throws UnknownHostException, IOException {
        if (getSocket() == null) {
            socket = new Socket(remoteHost, port);
        }
    }

    public Client() throws UnknownHostException, IOException {
        this(Constants.REMOTE_HOST, Constants.REMOTE_PORT);
    }

    public Socket getSocket() {
        return socket;
    }
}

Answer 1

You are correct. You have to close the client socket properly before exiting the client. Otherwise the operating system may reset the connection instead of closing it. Not being an Android guy I cannot advise you where this closure should be placed.

Your server has a problem too. It needs to catch EOFException in the read loop and silently break. At present you aren't handling end of stream correctly: you will catch it via catch (EOFException ) and log it as an error, which it isn't really.