Client/Server in one program (using multiple threads)?

Question

Is there some examples out there of how to use a client and server in a single program using separate threads? Also, is it possible to start a third thread to control the packets, such as drop a random or specified number of packets (or match on specific data in a packet)?

Answer 1

Just trying to have a client send udp packets to a server (all on the same machine running from the same program) and want to be able to drop packets coming from the client side to the server side.
E.g.,
Here's an example that I found here: http://compnet.epfl.ch/tps/tp5.html
import java.io.<strong>;
import java.net.</strong>;
import java.util.<strong>;
/</strong>
* Server to process ping requests over UDP.
public class PingServer {
     private static double lossRate = 0.3;
     private static int averageDelay = 100; // milliseconds
     private static int port;
     private static DatagramSocket socket;
     public static void main(String[] args) {
          // Get command line arguments.
          try {
               if (args.length == 0) {
                    throw new Exception("Mandatory parameter missing");
               port = Integer.parseInt(args[0]);
               if (args.length > 1) {
                    lossRate = Double.parseDouble(args[1]);
               if (args.length > 2) {
                    averageDelay = Integer.parseInt(args[2]);
          } catch (Exception e) {
               System.out.println("UDP Ping Server");
               System.out.println("Usage: java PingServer port [loss rate] [average delay in miliseconds]");
               return;
          // Create random number generator for use in simulating
          // packet loss and network delay.
          Random random = new Random();
          // Create a datagram socket for receiving and sending UDP packets
          // through the port specified on the command line.
          try {
               socket = new DatagramSocket(port);
               System.out.println("UDP PingSever awaiting echo requests");
          } catch (SocketException e) {
               System.out.println("Failed to create a socket");
               System.out.println(e);
               return;
          // Processing loop.
          while (true) {
               // Create a datagram packet to hold incoming UDP packet.
               DatagramPacket request = new DatagramPacket(new byte[1024], 1024);
               // Block until the host receives a UDP packet.
               try {
                    socket.receive(request);
               } catch (IOException e) {
                    System.out.println("Error receiving from socket");
                    System.out.println(e);
                    break;
               // Print the received data.
               printData(request);
               // Decide whether to reply, or simulate packet loss.
               if (random.nextDouble() < lossRate) {
                    System.out.println("   Reply not sent.");
                    continue;
               // Simulate network delay.
               try {
                    Thread.sleep((int) (random.nextDouble() * 2 * averageDelay));
               } catch (InterruptedException e) {}; // Ignore early awakenings.
               // Send reply.
               InetAddress clientHost = request.getAddress();
               int clientPort = request.getPort();
               byte[] buf = request.getData();
               DatagramPacket reply = new DatagramPacket(buf, buf.length,
                         clientHost, clientPort);
               try {
                    socket.send(reply);
               } catch (IOException e) {
                    System.out.println("Error sending to a socket");
                    System.out.println(e);
                    break;
               System.out.println("   Reply sent.");
      * Print ping data to the standard output stream.
     private static void printData(DatagramPacket request) {
          // Obtain references to the packet's array of bytes.
          byte[] buf = request.getData();
          // Wrap the bytes in a byte array input stream,
          // so that you can read the data as a stream of bytes.
          ByteArrayInputStream bais = new ByteArrayInputStream(buf);
          // Wrap the byte array output stream in an input stream reader,
          // so you can read the data as a stream of characters.
          InputStreamReader isr = new InputStreamReader(bais);
          // Wrap the input stream reader in a buffered reader,
          // so you can read the character data a line at a time.
          // (A line is a sequence of chars terminated by any combination of \r
          // and \n.)
          BufferedReader br = new BufferedReader(isr);
          // We will display the first line of the data.
          String line = "";
          try {
               line = br.readLine();
          } catch (IOException e) {
          // Print host address and data received from it.
          System.out.println("Received echo request from "
                    + request.getAddress().getHostAddress() + ": " + line);
}I'm looking to do the "processing loop" in a separate thread, but I'd also like to do the client in a separate thread
So you're saying, just put the client code in a separate class and start the thread and that's it? As far as the packet rate loss thread, is this possible to do in another thread?