public class Server implements Runnable {
    public static final int PORTNUMBER = 8540;
    public static final int MAX_CLIENTS = 3;
    public static boolean shutdownFlag = false;

    public static void main(String[] args) {
        Server s = new Server();
        s.run();

    }

@Override
public void run() {
    ExecutorService executor = null;
    try (ServerSocket serverSocket = new ServerSocket(PORTNUMBER);) {
        executor = Executors.newFixedThreadPool(MAX_CLIENTS);
        System.out.println("Waiting for clients");
        while (true) {
            Socket clientSocket = serverSocket.accept();
            //clientSocket.setSoTimeout(10000);
            Runnable worker = new RequestHandler(clientSocket);
            executor.execute(worker);
            System.out.println("Only printed if new Client arrives");
            if (shutdownFlag) {
                System.out.println("Executing shutdown");
                executor.shutdown();
                serverSocket.close();
            }
        }
    } catch (IOException e) {
        System.out
                .println("Exception caught when trying to listen on port "
                        + PORTNUMBER + " or listening for a connection");
        System.out.println(e.getMessage());
    } finally {
        if (executor != null) {
            executor.shutdown();
        }
    }

}

public class Client {

    public static final String HOSTNAME = "localhost";
    public static final int PORTNUMBER = 8540;
  public static void main(String[] args) throws IOException {



    try (Socket echoSocket = new Socket(HOSTNAME, PORTNUMBER);
      PrintWriter out = new PrintWriter(echoSocket.getOutputStream(), true);
//     InputStream test = echoSocket.getInputStream();
      BufferedReader in = new BufferedReader(new InputStreamReader(echoSocket.getInputStream()));
      BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in))) {
      String userInput;
      while ((userInput = stdIn.readLine()) != null) {
        out.println(userInput);
    System.out.println("echo: " + in.readLine());
    if(userInput.equals("BYE")){
        break;
    }

      }
    }catch (UnknownHostException e) {
       System.err.println("Don't know about host " + HOSTNAME);
       System.exit(1);
    }catch (IOException e) {
       System.err.println("Couldn't get I/O for the connection to " + HOSTNAME);
       System.exit(1);
    }

  }
}

public class RequestHandler implements Runnable {
    //private final String password = "passwort";
    private final Socket client;
    ServerSocket serverSocket = null;

    public RequestHandler(Socket client) {
        this.client = client;
    }

    @Override
    public void run() {
        try (BufferedReader in = new BufferedReader(new InputStreamReader(
                client.getInputStream()));
                BufferedWriter writer = new BufferedWriter(
                        new OutputStreamWriter(client.getOutputStream()));) {
            System.out.println("Thread started with name:"
                    + Thread.currentThread().getName());
            String userInput;
            String serverResponse;

            while ((userInput = in.readLine()) != null) {
                serverResponse = processInput(userInput);
                System.out.println("Received message from "
                        + Thread.currentThread().getName() + " : " + userInput);
                writer.write("Sever Response : " + serverResponse);
                writer.newLine();
                writer.flush();
            }
        } catch (IOException e) {
            System.out.println("I/O exception: " + e);
        } catch (Exception ex) {
            System.out.println("Exception in Thread Run. Exception : " + ex);
        }
    }

    public String processInput(String input) {
        boolean commandFound = false;
        String output = "";
        try {
            if (input.getBytes("UTF-8").length > 255)
                output = "Max string length exceeded";
        } catch (UnsupportedEncodingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        Pattern allPattern = Pattern
                .compile("(?<lower>^LOWERCASE\s.+)|(?<upper>^UPPERCASE\s.+)|(?<reverse>^REVERSE\s.+)|(?<bye>^BYE)|(?<shutdown>^SHUTDOWN passwort)");

        Matcher allMatcher = allPattern.matcher(input);
        if (allMatcher.find()) {
            String lower = allMatcher.group("lower");
            String upper = allMatcher.group("upper");
            String reverse = allMatcher.group("reverse");
            String bye = allMatcher.group("bye");
            String shutdown = allMatcher.group("shutdown");
            commandFound = true;
            if (lower != null) {
                output = lower.substring(10).toLowerCase();
            }
            if (upper != null) {
                output = upper.substring(10).toUpperCase();
            }
            if (reverse != null) {
                output = new StringBuilder(reverse.substring(8)).reverse()
                        .toString();
            }
            if (bye != null) {
                output = "BYE";
            }
            if (shutdown != null) {
                output = "SHUTDOWN";
                Server.shutdownFlag = true;
            }
        } else {
            commandFound = false;
            output = "UNKNOWN COMMAND";
        }


        if (commandFound) {
            output = "OK ".concat(output);
        } else {
            output = "ERROR ".concat(output);

        }
        return output;

    }
}

class Server {
     private boolean shutdownFlag = false; // This can't be static anymore.
     public static final Server SERVER = new Server();
     public static void main(String[] args) {
         SERVER.run();
     }
     private void run() {
         // Here goes everything that used to be inside main...
         // Now you have the Server.SERVER instance to use outside the class
         // to shut things down or whatever ...
     }
}