JavaFX and network

I am a novice in socket and network programming. This is my attempt to create a simple chat server. My code seems to have no errors (as far as I know). It compiles well, but when I try to run it, I seem to be in trouble and do nothing

Sorry, if such a thing has been asked, I can't find anything, but I'm not sure what the problem is, so I really don't know what to look for

The server:

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.socket;
import java.util.Date;

import javafx.scene.Scene;
import javafx.scene.control.TextArea;
import javafx.stage.Stage;

public class ChatServer extends Stage {
    TextArea informationArea = new TextArea();
    String message = null;

    public ChatServer() {
        informationArea.setEditable(false);
        setTitle("Chat Server");
        setScene(new Scene(informationArea,500,300));
        show();

        try {
            ServerSocket serverSocket = new ServerSocket(8000);
            informationArea.appendText("Server started at " + new Date() + '\n');

            int clientNumber = 1;

            while(true) {
                Socket socket = serverSocket.accept();
                InetAddress inetAddress = socket.getInetAddress();

                informationArea.appendText(
                    "Client: " + clientNumber++
                    + "\n\thost name: " + inetAddress.getHostName()
                    + "\n\tIP address " + inetAddress.getHostAddress() + "\n\n"
                );

                ClientHandler task = new ClientHandler(socket);
                new Thread(task).start();
            }
        } catch(IOException ex) {
            System.err.println(ex);
        }
    }

    class ClientHandler implements Runnable {
        private Socket socket;

        ClientHandler(Socket socket) {
            this.socket = socket;
        }

        @Override
        public void run() {
            try {
                DataInputStream inputFromClient = new DataInputStream(socket.getInputStream());
                DataOutputStream outputToClient = new DataOutputStream(socket.getOutputStream());

                while (true) {
                    if (message != null) {
                        outputToClient.writeUTF(message);
                    }
                    message = inputFromClient.readUTF();
                }
            } catch(IOException e) {
                System.err.println(e);
            }
        }
    }
}

The class that runs it:

import javafx.application.Application;
import javafx.stage.Stage;

public class RunChatServer extends Application {
    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage stage) {
        stage = new ChatServer();
    }
}

I appreciate the reasons for input errors, why, the correct way to achieve this goal, and suggestions of any style, because this is my first attempt, and I don't know the traditional way to achieve this goal

Update: I think maybe it's related to blocking UI threads. I added import JavaFX concurrent. Task and refactor my clienthandler class, as follows:

class ClientHandler extends Task {
        private Socket socket;

        ClientHandler(Socket socket) {
            this.socket = socket;
        }

        @Override
        public Void call() {
            try {
                DataInputStream inputFromClient = new DataInputStream(socket.getInputStream());
                DataOutputStream outputToClient = new DataOutputStream(socket.getOutputStream());

                while (true) {
                    if (message != null) {
                        outputToClient.writeUTF(message);
                        outputToClient.flush();
                    }
                    message = inputFromClient.readUTF();
                }
            } catch(IOException e) {
                System.err.println(e);
            }
            return null;
        }
    }

But it doesn't solve any problems

Solution

Instead of blocking the constructor, put the server's loop that accepts sockets in its own thread

try {
        ServerSocket serverSocket = new ServerSocket(8000);
        informationArea.appendText("Server started at " + new Date() + '\n');

        new Thread(() -> {
            int clientNumber = 1;
            while (true) {
                try {
                    Socket socket = serverSocket.accept();
                    InetAddress inetAddress = socket.getInetAddress();

                    Platform.runLater(() -> 
                        informationArea.appendText(
                            "Client: " + clientNumber++
                            + "\n\thost name: " + inetAddress.getHostName()
                            + "\n\tIP address " + inetAddress.getHostAddress() + "\n\n"
                        )
                    );

                    ClientHandler task = new ClientHandler(socket);
                    new Thread(task).start();
                } catch (IOException ex) {
                    Logger.getLogger(ChatServer.class.getName()).log(Level.SEVERE,null,ex);
                }
            }
        }).start();

    } catch (IOException ex) {
        System.err.println(ex);
    }