How the Java server perceives the client disconnection

I have two questions:
how does the 1.java server perceive client chain breakage
2. Optimal implementation of a Server supporting multiple client connections
description:
for problem 1: the problem is that in the following code, when the client breaks the chain, the, while (true) always loops, causing the output to be null
for problem 2: my current implementation is that every client connection opens a thread to handle it, which does not feel reasonable, because when thousands of clients go to connect, It is impossible to create a process in this way, seeking the optimal solution.

I hope you will not hesitate to give us your advice. Thank you. The Java server code is as follows. The function is to start a server, connect with other clients, and output directly according to the messages sent by the client:

package MyTCP;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.channels.NonWritableChannelException;

public class Server
{
    public static void main(String[] args)
    {
        
        StartListen();
    }
    
    /**
     * 
     */
    public static void StartListen()
    {
        int port = 10001;
        createTCP(port);
    }
    
    /**
     * 
     * @param port
     * @param address
     */
    public static void createTCP(int port)
    {
        try
        {
            ServerSocket serverSocket = new ServerSocket(port);
            System.out.println("server list on 127.0.0.1:10001");
            
            while (true)
            {
                Socket socket = serverSocket.accept();
                new Thread(new ChildThred(socket)).start();
            }
        } 
        catch (IOException e) 
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

class ChildThred implements Runnable
{
    BufferedReader bufrea = null;
    Socket socket = null;
    public ChildThred(Socket socket)
    {
        this.socket = socket;
    }

    @Override
    public void run()
    {
        try
        {
            bufrea = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            
            while(true)
            {    
                System.out.println(" : " + bufrea.readLine());    
            }
            
        }
        catch (Exception e)
        {
            // TODO: handle exception
            e.printStackTrace();
        }
        finally 
        {
            try
            {
                bufrea.close();
                socket.close();
            }
            catch (Exception e) 
            {
                System.out.println(e.getMessage());
            }
        }
    }
}

Java

Feb.21,2022