EchoServer

package tcplistener;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;

/**
 * Handles connections on a thread pool and invokes the handle method as
 * implemented by an instance of the ConnectionHandler interface when a
 * connection is established
 *
 * @author Dialog
 */
public class EchoServer implements Runnable
{

    /**
     * Maximum number of threads to use
     */
    private static final int MAX_THREADS = 5;

    /**
     * Port to listen on
     */
    private static final int PORT = 8080;

    /**
     * Underlaying socket which is used for remote I/O operations
     */
    private final Socket SOCKET;

    /**
     * Defines behavior for when a response from the server is expected
     */
    private final ConnectionHandler HANDLER;

    /**
     * Simply initializes a new EchoServer object which echoes everything sent
     * to us back
     *
     * @param socket Socket to read from and write to
     * @param handler Defines behavior for when a response from the server is
     * expected
     */
    public EchoServer(Socket socket, ConnectionHandler handler)
    {
        this.SOCKET = socket;
        this.HANDLER = handler;
    }

    @Override
    public void run()
    {
        try (BufferedReader in = new BufferedReader(
                new InputStreamReader(SOCKET.getInputStream())))
        {
            String line;

            while ((line = in.readLine()) != null)
            {
                HANDLER.handle(SOCKET, line);
            }
        } catch (IOException ex)
        {
            //Socket has most likely been closed
        }
    }

    /**
     * Starts a thread pool and listens for incoming connections on the
     * specified port, then handles all connections over seperate threads
     *
     * @param args the command line arguments
     * @throws IOException Thrown if an I/O exception occurs while opening the
     * socket or
     */
    public static void main(String[] args) throws IOException
    {
        ServerSocket listener = new ServerSocket(PORT);
        Executor executor = Executors.newFixedThreadPool(MAX_THREADS);

        ConnectionHandler handler = new ConnectionHandler()
        {

            @Override
            public void handle(Socket socket, String content)
            {
                try (PrintWriter out = new PrintWriter(socket.getOutputStream()))
                {
                    out.write("Server says: " + content);

                    System.out.printf("Echoed \"%s\" to %s\n", content,
                            socket.getRemoteSocketAddress().toString());
                } catch (IOException ex)
                {
                    System.err.println("IOException: " + ex.getMessage());
                }
            }
        };

        System.out.printf("Accepting connections on port %d...\n", PORT);

        while (true)
        {
            Socket socket = listener.accept();
            executor.execute(new EchoServer(socket, handler));
        }
    }
}

/**
 * Classes implementing this interface define behavior which can be called by
 * EchoServer to handle an incoming connection
 *
 * @author Dialog
 */
interface ConnectionHandler
{

    /**
     * Defines behavior for when a response from the server is expected
     *
     * @param socket Socket to read from and write to
     * @param handler Defines behavior for when a response from the server is
     * expected
     */
    public void handle(Socket socket, String content);
}