Code:

/*

ServerThreaded.java
-------------------

Multithreaded server listens custom port and echoes requests.

Compile with
    javac ServerThreaded.java

*/


import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStreamReader;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.concurrent.Executors;


// main class accepts clients and gives them to a thread
class ServerThreaded
{
    public static void main(String args[])
    {
        java.util.concurrent.Executor threadPool = Executors.newFixedThreadPool(3);
        
        try
        {
            ServerSocket server = new ServerSocket(9000);
            if (server.isBound())
            {
                System.out.println("main():listening...");
                while (true)
                {
                    Socket client = server.accept();
                    threadPool.execute(new Run(client));
                }
            }
        }
        catch (IOException e)
        {
            System.out.println("ServerThreaded.main():e=" + e);
        }
    }
}


// talks with a single client
class Run implements Runnable
{
    public Run(Socket client)
    {
        this.client = client;
    }
    
    public void run()
    {
        try
        {
            System.out.println("this.client.getRemoteSocketAddress()=" + this.client.getRemoteSocketAddress());

            // read client request
            byte request[] = new byte[100];
            this.client.getInputStream().read(request, 0, 100);
            System.out.println("Run.run():request=" + new String(request));

            // send response same as request
            System.out.println("Run.run():this.client.isClosed()=" + this.client.isClosed() + ",this.client.isConnected()=" + this.client.isConnected());
            this.client.getOutputStream().write(request);

            this.client.close();
        }
        catch (IOException e)
        {
            System.out.println("Run.run():e=" + e);
        }
    }
    
    private Socket client;
}