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    <p>The problem is that the declaration of <code>Socket fromClient = server.accept();</code> on the server is inside the scope of the <code>for</code> loop. So at the end of the <code>for</code> loop (after <code>serverOutput.flush();</code>) the <code>fromClient</code> variable is destroyed and a new one is created the next time the loop begins. You will need to restructure it like this if you want the same connection to be able to send/receive multiple messages:</p> <pre><code>import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.net.Socket; import java.net.UnknownHostException; import java.util.HashMap public class User extends Runnable { public String username; public Socket socket; public TestServer testServerReference; ObjectInputStream clientInput; ObjectOutputStream serverOutput; public User(Socket s, TestServer tS) { socket = s; testServerReference = tS; } /** * Creates the in/out Streams, returns the username */ public String init() { serverOutput = new ObjectOutputStream (fromClient.getOutputStream()); clientInput = new ObjectInputStream (fromClient.getInputStream()); this.username = (String)clientInput.readObject(); //the first thing the client should send is a username } public void run() { try { //add send/receive logic here for connected client } catch (Exception ex) { } finally { testServerReference.removeUser(username); } } } public class TestServer { public static HashMap&lt;String,User&gt; userList = new HashMap&lt;String,User&gt;(); public static void main(String[] args) { try { ServerSocket server = new ServerSocket(5555, 100); while (true) //start accepting new connections { System.out.println ("Listening for connections"); Socket fromClient = server.accept(); User newUser = new User(fromClient,this); String newUsername = newUser.init(); userList.add(newUsername,newUser); (new Thread(newUser)).start(); } } catch (ClassNotFoundException ex) { Logger.getLogger(TestServer.class.getName()).log(Level.SEVERE, null, ex); } catch (IOException ex) { Logger.getLogger(TestServer.class.getName()).log(Level.SEVERE, null, ex); } } public static void removeUser(String username) { userList.remove(username); } } </code></pre> <p>I just threw this code together really quickly and have not yet test compiled it, so it may still contain a couple errors, but the general idea is there.</p>
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    1. PORe-use a java socket client once again
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    1. COHi aioi222, Thanks for the answer but that is not what I am looking for. The server.accept must be in the loop to pile them up when many client requests are sent to the same server at the same time. The problem here is that means that "new ObjectInputStream" must be done within the loop, which means the client at the other side does not know that its Outputstream is now lose, sending the message to no-one.
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    2. COhmm just realized the problems comes from the fact that the socket is re-written hence from the client perspective, the other end is not responding any more. Shall find out the solution and post it back here
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    3. COThere are a number of solutions to this. Each time that a new user connects you will need to save off that socket and the associated streams to a List. You could then spawn a new listener thread for each connection that handles sending/receiving messages for the associated socket. Another option is to have a single thread that listens for new connections and a single thread that iterates through all the connections and checks them for new input and sends new output to them. A third option would be to set timeouts on the sockets and socket acceptor and do it all from a single thread.
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