Multiple OutputStreams to a single socket

Question

Hi,
I searched the forums but could not find an answer for this.
I have a socket between a server and a client and am already using an output stream to send information via this output stream.
Now, I want to use another thread and another output stream to the same socket to send more data to the client. Is this possible? Are there synchronization problems or would the messages from both threads clutter each other in the socket? Is the multiplexing between the (text) messages from the 2 streams done in the lower layers of the TCP socket? Can I get away with using this or should I redesign my means of communication? I might also move towards object serialization in the future for my messages.
I wrote two sample programs and the result looks ok, but I want to check to see if there are no issues with this. The test client creates 3 threads that get different output streams from the same socket and then send their name to the server independently and randomly. The server receives text messages via the socket and prints them out. I do flush all me messages and only send text messages. From the output it looks like the messages are not clobbered and are received randomly. I also did the test without the randomness and saw no problems.
thanks,
Clive.
My server code:
import java.io.*;
import java.net.*;
public class EchoServer {
  public static void main(String[] args) throws IOException {
    Socket echoSocket = null;
    PrintWriter out = null;
    BufferedReader in = null;
    try {
      System.out.println("Starting server... ");
      ServerSocket serverSocket = new ServerSocket(60000);
      System.out.println("Waiting for client at 60000 ... ");
      echoSocket = serverSocket.accept();
      System.out.println("Connected to client at 60000");
      in = new BufferedReader(new InputStreamReader(
                                  echoSocket.getInputStream()));
    } catch (UnknownHostException e) {
      System.err.println("Don't know about host: " + e.getMessage());
      System.exit(1);
    } catch (IOException e) {
      System.err.println("Couldn't get I/O for "
                         + "the connection to: " + e.getMessage());
      System.exit(1);
    String userInput;
    while ((userInput = in.readLine()) != null) {
      System.out.println("echo: " + userInput);
    System.out.println("Closing the socket");
    in.close();
    echoSocket.close();
  } // main
}My client code:
import java.io.*;
import java.net.*;
import java.util.*;
public class EchoClient {
  public EchoClient() {
    Socket echoSocket = null;
    PrintWriter out1 = null;
    BufferedReader in = null;
    MyWriter thread1 = null;
    MyWriter thread2 = null;
    MyWriter thread3 = null;
    try {
      System.out.println("Connecting to localhost");
      echoSocket = new Socket("localhost", 60000);
      thread1 = new MyWriter(echoSocket, "name1");
      thread1.start();
      thread2 = new MyWriter(echoSocket, "name2");
      thread2.start();
      thread3 = new MyWriter(echoSocket, "name3");
      thread3.start();
    } catch (UnknownHostException e) {
      System.err.println("Don't know about host: " + e.getMessage());
      System.exit(1);
    } catch (IOException e) {
      System.err.println("Couldn't get I/O for "
                         + "the connection to: " + e.getMessage());
      System.exit(1);
  } // cons
  public class MyWriter extends Thread {
    PrintWriter out = null;
    String name;
    public  MyWriter(java.net.Socket socket, String name) {
      super(name);
      try {
        out = new PrintWriter(socket.getOutputStream(), true);
        this.name = name;
      } catch (IOException ioe) {
        System.err.println("Could not get output stream for " + name);
    public void run() {
      String userInput;
      Random r = new Random();
      boolean myTruth = true;
      try {
        while(myTruth) {
          out.println( this.name );
          System.out.println("sent " + this.name);
          Thread.sleep(r.nextInt(200));  // send the info randomly
      } catch(InterruptedException ie) {
        System.err.println("Could not wait for " + name);
      out.close();
  } // class MyWriter
  public static void main(String[] args) throws IOException {
    EchoClient echo = new EchoClient();
  } // main
}Server Output:
Connected to client at 60000
echo: name1
echo: name2
echo: name3
echo: name1
echo: name2
echo: name3
echo: name1
echo: name2
echo: name3
echo: name3
echo: name1
echo: name2
echo: name3
echo: name1
echo: name1

Answer 1

It is certainly doable, but you'll need to do some work here.
Probably what i would do is write a Multiplexor stream that sits on top of the raw tcp stream.
Implement this stream to implement synchronization such that only one client stream can write at a time. Further each stream should have a unique id associated with it, and registered with the base Multiplexor stream, so that when it writes into the down stream, it can prefix the data with its id. In that way the reader of the stream can see where to forward the data to.
If some other stream tries to write to the Base Multiplexor stream an exception should be thrown, since it hasn't registered itself.
There is a book by Manning that is pretty good in this area.
http://www.manning.com/Hughes/