Java - Concurrent Server Using Threads

Server
Thread

import java.net.*;
import java.io.*;

public class KKMultiServer {
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = null;
boolean listening = true;

try {
serverSocket = new ServerSocket(4444);
} catch (IOException e) {
System.err.println("Could not listen on port: 4444.");
System.exit(-1);
}

while (listening)
new KKMultiServerThread(serverSocket.accept()).start();

serverSocket.close();
}
}



import java.net.*;
import java.io.*;

public class KKMultiServerThread extends Thread {
private Socket socket = null;

public KKMultiServerThread(Socket socket) {
super("KKMultiServerThread");
this.socket = socket;
}

public void run() {

try {
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(
socket.getInputStream()));

String inputLine, outputLine;
KnockKnockProtocol kkp = new KnockKnockProtocol();
outputLine = kkp.processInput(null);
out.println(outputLine);

while ((inputLine = in.readLine()) != null) {
outputLine = kkp.processInput(inputLine);
out.println(outputLine);
if (outputLine.equals("Bye"))
break;
}
out.close();
in.close();
socket.close();

} catch (IOException e) {
e.printStackTrace();
}
}
}