Sockets work on localhost but not remotely?

Question

hi there,
I have created a simple multithreaded client / server program.
The Server listens on port 2222 for clients. When a client connects - the client sends its ip address to the server and then disconects. More than 1 client can connect at the same time to the server and the server also listens continuasly. I have 2 problems with the program...
a) the programs work on localhost but not on remote machines? (Well not over my LAN anyway).
b) I am getting 2 lots of 'datain' when the server recieves an ip address from the client when the client should only send it once.
The code is below - any help would be greatly appreciated.
//TCPServer.java
import java.io.*;
import java.net.*;
class TCPServer {
     public static void main (String args[]) throws IOException {
          ServerSocket serverSocket = null;
          boolean listening = true;
          try {
               serverSocket = new ServerSocket(2222);
          } catch (IOException e) {
               System.err.println("Could not listen on port: 2222");
               System.exit(-1);
          System.out.println("Server Started...\n");
          while (listening)
          new TCPServerThread(serverSocket.accept()).start();
          serverSocket.close();
//TCPServerThread.java
import java.net.*;
import java.io.*;
public class TCPServerThread extends Thread {
    public Socket socket;
    public TCPServerThread(Socket socket) {
     super("TCPServerThread");
     this.socket = socket;
    public void run() {
               try {
               BufferedReader datain = new BufferedReader (new InputStreamReader
                    (socket.getInputStream()));
                    System.out.println("ip address recieved");
                    System.out.println (datain.readLine () + "\n");
               } catch (IOException e) {
                    System.err.println("Cannot read in ip address\n");
                    e.printStackTrace(); // show the error
                    System.exit(-1);
     } //TCPClient.java
import java.io.*;
import java.net.*;
class TCPClient {
     public static void main (String args[]) throws Exception
          String hostname;
          int portNumber;
          String portString;
          BufferedReader inFromUser =
               new BufferedReader (new InputStreamReader(System.in));
               System.out.println("What host would you like to connect to?");
               hostname = inFromUser.readLine();
               System.out.println("What port would you like to connect to?");
               portString = inFromUser.readLine();
               portNumber = Integer.parseInt(portString);
               System.out.println("Connecting to port " + portNumber + " of " + hostname + "....\n");
                    Socket clientSocket = new Socket(hostname, portNumber);
                    Socket sock = new Socket (InetAddress.getLocalHost(), portNumber);
                    BufferedWriter dataout;
                    java.net.InetAddress i = java.net.InetAddress.getLocalHost();
                    System.out.println("Sending ip address...\n" + i.getHostAddress());
                         dataout = new BufferedWriter (new OutputStreamWriter (sock.getOutputStream()));
                              dataout.write (i.getHostAddress());
                              dataout.flush();
                              sock.close();
                                   clientSocket.close();
                         }Oh, yeah - check out my site below, I am trying to write an audio streaming client / server in Java if anyone is interested in getting involved or just being nosey....
http://www.projectg.dsl.pipex.com

Answer 1

In your client you are creating two sockets (why?). One connected to localhost, the other connected to the host specified using readLine.
If your client runs on the same machine you have started your server, you have two connects to your server instead of one.
The ip adresse is sent using the socket connected to localhost. That is why it does not work on remote machines.
Hope this helps.
Jörg