Multiple clients on socket connection

Question

Hi!
I understand that it is possible that multiple clients listen to one server (on the same port) and even write to it (then it should be a multi-threaded server).
But i would like to refuse connectios, if one client is connected. How can I do that?
In my case I have a (single threaded) server. Now one clients connects. The server waits to receive data from the client and answers, without ever closing the port. that works.
Now if I connect with a second client, the openicng of the socket in the second client works fine, although the server does not seem to notice the second client. Communication is not possible between the server and the second client, and the server doesn't answer to the first client anymore, although he receives data from it.
So, since the server does not seem to notice the second client (does not accept the connection) and I don't get an exception at the second client, what can I do?
Thank you for your help!
concerned Code (if you want to take a look at it):
CLIENT:
socket = new Socket(hostname, echo_port);
SERVER:
try
ServerSocket waitingsocket = new ServerSocket(echo_port);
try
     socket= waitingsocket.accept();
     System.out.println("Client connected");
     ReaderThread reader = new ReaderThread( this, socket );
     reader.start();          
catch (Exception e)
READER:
public void run()
     while (true)
          try {
               int bytesRead = inStream.read(inputBuffer,
               0, inputBuffer.length);
               readCallback.tcpUpdate(inputBuffer,bytesRead);
          catch (Exception oops)
               readCallback.tcpUpdate(null,-1);
          

Answer 1

Just to make sure this is clear: You can NOT have multiple clients on a given socket connection. You CAN have multiple clients connected to a particular port on a given server, but each client will be communicating with the server through a different of socket.
The usual approach here is to set up a listening ServerSocket on the desired port, call accept() on it, then process the communication from the returned Socket object. This is usually done by spawning a new thread and allowing it to handle the socket communication, while the ServerSocket loops around to another accept() for the next communication.
Here's an excellent intro to the concepts (the code is really ugly and poorly implemented, but it does a good job of explaining the overall concept). I used this as a starting point, and now (after a whole lot of development) have a pretty sweet extensible web server class that handles template expansion, etc... (I use this as a quick and dirty UI for some of my apps, instead of requiring the user to install a JSP container):
http://developer.java.sun.com/developer/technicalArticles/Networking/Webserver/
- K