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The best way to bind list with other components in multi-threaded javafx application

I'am creating application to making screenshots via LAN. Server is
listening for clients. When client is connect, new thread is created and it shoud be added to a list. Admin on server can pick client from list, make screenshot on its computer and screenshot is sent to server. The problem is the list. How to make this list available in many places in app and it was always synchronized with all components that use it ?
I am using JavaFX. I readed about SimpleListProperty, but the problem was "how to use this instance in server thread?". I've tried with singletone variations, dependencies injection like Guice, Ignite, Spring, but it was generated many troubles and finally doesn't work :(
Server implementation
public class SocketServer extends Thread {
private ServerSocket serverSocket;
#Override
public void run() {
startServer();
}
private void startServer() {
try {
serverSocket = new ServerSocket(2345);
} catch (IOException e) {
e.printStackTrace();
}
while (true) {
try {
new EchoClientHandler(serverSocket.accept()).run();
} catch (IOException e) {
e.printStackTrace();
}
}
}
public void stopServer() {
try {
serverSocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public class EchoClientHandler extends Thread {
private Socket clientSocket;
private PrintWriter out;
private BufferedReader in;
public EchoClientHandler(Socket socket) {
this.clientSocket = socket;
}
#Override
public void run() {
try {
out = new PrintWriter(clientSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
} catch (IOException e) {
e.printStackTrace();
}
//there shoud be somethink like:
// list.add(this);
}
public void close() {
try {
in.close();
out.close();
clientSocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
//Getters and setters
MainController
public class MainController {
#FXML
private LogPaneController logPaneController;
#FXML
private ConnectionPaneController connectionPaneController;
#FXML
private ButtonsPaneController buttonsPaneController;
private Connector connectorImpl;
public void initialize() {
createConnector();
}
private void createConnector() {
ObservableList<Client> observableList = connectionPaneController.getConnectedClientsTable().getItems();
connectorImpl.setClientSimpleListProperty(observableList);
}
Connector
public class ConnectorImpl implements Connector {
private List<SocketServer.EchoClientHandler> clientsThreads;
private SimpleListProperty<Client> clientSimpleListProperty;
public ConnectorImpl() {
}
public static Client parseThreadToClient(SocketServer.EchoClientHandler clientThread) {
Socket socket = clientThread.getClientSocket();
PrintWriter out = clientThread.getOut();
BufferedReader in = clientThread.getIn();
return new Client(socket, out, in);
}
#Override
public void connectNewClient(SocketServer.EchoClientHandler clientThread) {
clientsThreads.add(clientThread);
clientSimpleListProperty.add(parseThreadToClient(clientThread));
}
//Getters and setters
}
App view

why java tcp server is accepting closed socket?

I have a class A that accepts TCP connection and send this new socket to Thread B where data from that socket is received and sent.
Class A{
Class b = new B();
public void run()
{
b.start();
while(true){
Socket socket = serverSocket.accept();
if(socket==null || socket.isClosed())continue;
b.setSocket(socket);
}
}
}
Class B extends Thread{
Socket socket;
public void setSocket(Socket p_socket) throws IOException
{
if(socket!=null && !socket.isClosed())
{
try{
socket.close();
socket = null;
Thread.sleep(5);
}
catch(Exception ex)
{}
}
socket = p_socket;
inputStream = socket.getInputStream(); // Here I am getting socket.closed() exception very much.
}
This worked fairly good in the past but now recently I am very very frequently getting the following error.
java.io.IOException: Socket Closed
at java.net.AbstractPlainSocketImpl.getInputStream(AbstractPlainSocketImpl.java:421)
at java.net.Socket$2.run(Socket.java:914)
at java.net.Socket$2.run(Socket.java:912)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.Socket.getInputStream(Socket.java:911)
I don't understand why this is happening now after years of working fine. Is this due to the network problem or Thread related something?
Updated:
Can this be the server related problem? Because the same application is running on other server but they are not having this problem.

The whole setup concept looks a bit broken. You should not "change" resources from the outside, while maybe there is still some work going on in that thread. A way better concept is to encapsulate the Socket into a new worker thread:
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
public class WrapHandler {
static public class Server {
private final ServerSocket mSocket;
private final ArrayList<Handler> mRunningHandlers = new ArrayList<>();
public Server(final int pPort) throws IOException {
mSocket = new ServerSocket(pPort);
new Thread(() -> mainLoop()).start();
}
private void mainLoop() {
while (true) {
try {
#SuppressWarnings("resource") final Socket socket = mSocket.accept(); // do not close, do not handle with resource, socket will be closed by handler!
final Handler h = new Handler(socket, this);
handlerStarted(h);
} catch (final IOException e) {
e.printStackTrace(); // do something useful
}
}
}
synchronized void handlerStarted(final Handler pHandler) {
mRunningHandlers.add(pHandler);
}
synchronized void handlerEnded(final Handler pHandler) {
mRunningHandlers.remove(pHandler);
}
void handleException(final Handler pHandler, final Throwable pException) {
/* again do something useful */
}
}
static public class Handler {
private final Socket mSocket;
private final Server mServer;
public Handler(final Socket pSocket, final Server pServer) {
mSocket = pSocket;
mServer = pServer;
new Thread(() -> handleSocket()).start();
}
private void handleSocket() {
try {
handleData();
} catch (final IOException e) {
mServer.handleException(this, e);
} finally {
mServer.handlerEnded(this);
stop();
}
}
private void handleData() throws IOException {
mSocket.getInputStream().read();
/* data handling code here */
}
void stop() {
try {
mSocket.close();
} catch (final IOException e) { /* ignore or handle as you will */ }
}
}
}

Multithreaded server running on Tomcat 9

I tried finding a question that covered my problem, but all I could find were lots of similar questions, but no answer that solved my problem.
I am creating a java webapp for Tomcat, that, between other things, must also act as a TCP server that handles multiple incoming connections: to do so, I run the TCP server code in a separate thread, which in turn uses a ExecutorService to create threads for each connection. The problem basically is that, when I stop Tomcat, the server thread never gets stopped (even if no one has connected yet) and hangs Tomcat, until I close the related process in the Task Manager.
So, this is the starting point of the program:
private TCPServer tcpServer;
Thread serverThread;
#Override
public void init() throws ServletException {
DBConn = getDBConn();
if (DBConn != null) {
//initiates loggers, reads configurations from a file, etc
//starts TCP server
tcpServer = new TCPServer(50001, 200);
serverThread = new Thread(tcpServer);
serverThread.start();
//will be doing other stuff
} else {
//handles DB connection failure
}
}
This is the TCPServer class:
public class TCPServer implements Runnable {
private final int listeningPort;
PrintWriter out;
BufferedReader in;
ServerSocket serverSocket;
private final ExecutorService pool;
public TCPServer(int port, int poolSize) {
listeningPort = port;
pool = Executors.newFixedThreadPool(poolSize);
}
#Override
public void run() {
LinkedBlockingQueue<Socket> queue = new LinkedBlockingQueue<>();
try {
serverSocket = new ServerSocket(listeningPort);
while (!Thread.currentThread().isInterrupted()) {
pool.execute(new ConnectionHandler(queue));
queue.put(serverSocket.accept());
}
} catch (IOException | InterruptedException ex) {
Logger.getLogger(TCPServer.class.getName()).log(Level.SEVERE, null, ex);
}
}
private class ConnectionHandler implements Runnable {
private LinkedBlockingQueue<Socket> socketQueue;
public ConnectionHandler(LinkedBlockingQueue<Socket> queue) {
this.socketQueue = queue;
}
#Override
public void run() {
while (!Thread.interrupted() || !Thread.currentThread().isInterrupted()) {
try (Socket clientSocket = socketQueue.take()) {
in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
String line = in.readLine();
System.out.println("Incoming: " + line);
clientSocket.close();
} catch (InterruptedException ex) {
Logger.getLogger(TCPServer.class.getName()).log(Level.SEVERE, null, ex);
} catch (IOException ex) {
Logger.getLogger(TCPServer.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
public void close(){
Thread.currentThread().interrupt();
try {
serverSocket.close();
} catch (IOException ex) {
Logger.getLogger(TCPServer.class.getName()).log(Level.SEVERE, null, ex); }
pool.shutdownNow();
}
}
I added, in the main class (the same where the init() above is), this override, that runs when Tomcat gets closed:
#Override
public void contextDestroyed(ServletContextEvent sce) {
serverThread.interrupt();
tcpServer.close();
ServletContextListener.super.contextDestroyed(sce);
}
I made so many edits trying to implement solutions that I found around on the internet, that surely some of this code is probably redundant or useless.
Can someone give me pointers on what I should do to correctly stop the TCPServer thread?

Thanks to this answer and Kayaman's comment, I revised the whole code and somehow got it working.
The init() override is the same, while the contextDestroyed override now is
#Override
public void contextDestroyed(ServletContextEvent sce) {
tcpServer.close();
serverThread.interrupt();
ServletContextListener.super.contextDestroyed(sce);
}
The TCPServer class now is:
public class TCPServer implements Runnable {
private final int listeningPort;
PrintWriter out;
BufferedReader in;
ServerSocket serverSocket;
private final ExecutorService pool;
public TCPServer(int port, int poolSize) {
listeningPort = port;
pool = Executors.newFixedThreadPool(poolSize);
}
#Override
public void run() {
try {
serverSocket = new ServerSocket(listeningPort);
while (!Thread.currentThread().isInterrupted()) {
Socket clientSocket = serverSocket.accept();
pool.submit(new ConnectionHandler(clientSocket));
}
} catch (IOException ex) {
Logger.getLogger(TCPServer.class.getName()).log(Level.SEVERE, null, ex);
} finally {
pool.shutdown();
}
}
private class ConnectionHandler implements Runnable {
private Socket sock;
public ConnectionHandler(Socket sock){
this.sock = sock;
}
#Override
public void run() {
while (!Thread.currentThread().isInterrupted()) {
try{
in = new BufferedReader(new InputStreamReader(sock.getInputStream()));
String line = in.readLine();
System.out.println("Incoming: " + line);
sock.close();
} catch (IOException ex) {
Logger.getLogger(TCPServer.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
}
public void close(){
try {
serverSocket.close();
} catch (IOException ex) {
Logger.getLogger(TCPServer.class.getName()).log(Level.SEVERE, null, ex);
}
}
}

Java Socket ] instance of DataInputStream is print continue null

I'm making Chatting-Room program using the Java Swing.
In the client side, I was saw that doesn't read message from the server side.
The writeUTF() method of the client side is very well and I'm checked readUTF and writeUTF on the server side, that was very well too.
I think the problem is code which does as "Receiver" on the client side.
In the run() method of Thread, The instance dis of the DataInputStream has continuously null value.
I'm so confusing.. Please give me some help.
The bellow is part of my client&server code.
Thanks!
Client code
RoomBackground.java
public class RoomBackground {
private static String socket_server = "127.0.0.1";
private static Socket chatSocket;
private static DataOutputStream dos;
private static DataInputStream dis;
private ChatReceiver chatReceiver;
public Socket getChatSocket() {
return chatSocket;
}
public static DataOutputStream getDos() {
return dos;
}
public RoomBackground() throws IOException {
chatSocket = new Socket(socket_server, 7777);
chatReceiver = new ChatReceiver();
chatReceiver.start();
dos = new DataOutputStream(chatSocket.getOutputStream());
dis = new DataInputStream(chatSocket.getInputStream());
dos.writeUTF(User.getUser().getUsername());
dos.flush();
}
class ChatReceiver extends Thread {
#Override
public void run(){
try {
# PROBLEM CODE..... Allways "dis is null"
System.out.println("dis is " + dis);
# This line never executed.
while(dis != null) {
# some codes.....
}
} catch (IOException e) {
e.printStackTrace();
System.out.println(e.toString());
} catch (BadLocationException e) {
e.printStackTrace();
}
}
}
}
RoomFrame.java
public class RoomFrame extends JFrame{
private RoomBackground roomBackground;
public RoomFrame(int roomId) throws IOException {
chatField.addActionListener(new ActionListener() {
roomBackground = new RoomBackground();
#Override
public void actionPerformed(ActionEvent e) {
String msg = chatField.getText() + "\n";
try {
RoomBackground.getDos().writeUTF(msg);
# It works.
System.out.println("sent msg is " + msg);
} catch (IOException e1) {
e1.printStackTrace();
}
chatField.setText("");
}
});
}
}
Now server code.
Server Background.java
public class ChatReceiver extends Thread {
private DataInputStream in;
private DataOutputStream out;
public ChatReceiver(Socket chatSocket) throws IOException {
out = new DataOutputStream(chatSocket.getOutputStream());
in = new DataInputStream(chatSocket.getInputStream());
nick = in.readUTF();
addChatClient(nick, out);
}
#Override
public void run() {
try {
while(in!=null) {
chatMsg = in.readUTF();
# It works !
System.out.println("before send" + chatMsg);
sendMsg(chatMsg);
# It works too!
System.out.println("after send" + chatMsg);
}
}catch (IOException e) {
removeChatClient(nick);
}
}
}

When you are starting the ChatReceiver thread in the RoomBackground the dis object is not initialized yet, that is why it is null. One solution could be to initialize the dis variable in the ChatReceiver constructor.

java chat system,issue in sending & recieving

My program is set & ready, the problem is within the server. When I clients send the message, where should it be stored at ? I tried using queue but didn't work, also tried to use a usual string register but it worked partially. I made a thread for the sending & a thread for storing, using "Read/write UTF". I would be more than grateful if somebody provided me with an algorithm , or at a least a better idea. Code :
class clientThread extends Thread {
DataInputStream fromClient;
int counter = 0;
public clientThread(Socket cs) throws IOException
{
fromClient = new DataInputStream(cs.getInputStream());
}
public void run()
{
while (true)
{
try {
toall=Integer.toString(counter)+fromClient.readUTF();
} catch (IOException ex) {
Logger.getLogger(ChatTerminalS.class.getName()).log(Level.SEVERE, null, ex);
}
counter++;
}
}
}
class SendingThread extends Thread
{
DataOutputStream toClient;
String s = "";int counter=0;
public SendingThread(Socket cs) throws IOException
{
toClient = new DataOutputStream(cs.getOutputStream());
}
public void run()
{
while (true)
{
if(toall.charAt(0)+""==Integer.toString(counter))
{}
else
{
try {
toClient.writeUTF(toall);
} catch (IOException ex) {
Logger.getLogger(ChatTerminalS.class.getName()).log(Level.SEVERE, null, ex);
}
counter++;
}
}
}