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copied!<p>Your 'n' thread has no loop, meaning its gonna run once (accept a connection), then die off.</p> <pre><code>Thread n = new Thread(new Runnable() { public void run() { while(true) { //control this with your own boolean, or it will run forever try { addClient(); }catch(IOException e) { } } } }); </code></pre> <p>Dont worry, your thread will be paused at 'ss.accept()', since it will wait until a socket is accepted to continue.</p> <pre><code>Thread thread = new Thread(new Runnable() { public void run() { while(running) { String input; while((input = inputstream.readUTF()) != null) { //handle input } } } }); </code></pre> <p>Sorry, wrote that really quick, dont have much time. Ill come back and relate it to your code in a bit if it doesnt help.</p> <p>You need some way of continuously retrieving input from the Server's input stream, in which you can then handle the input.</p> <p>That loop loops each time you retrieve something from inputstream.readUTF() (and isnt null, of course). Hopefully that example will help you</p> <hr> <p>After actually reading your code and testing it, i have noticed that your structure seems a bit off. First, your <code>Thread n</code> in your server is responsible for accepting connections (<code>addClient()</code>), but you also call it first thing in your <code>Thread input</code>? </p> <p><code>Thread n</code> is handling accepting connections, so with the loop, <code>Thread n</code> is fine. <code>Thread input</code> is handling input retrieved from clients. This is where you are getting confused.</p> <p>Each client should have their own InputStream and OutputStream server-sided. Similar to how you have a list for Sockets (since you are gonna be creating multiple Sockets server-sided), you need multiple Streams aswell. For this, I suggest making a User class, then if anything, have your ArrayList for User, not Socket.</p> <pre><code>public class User extends Thread { //create a Thread for each connection to handle data seperately DataInputStream in; DataInputStream out; Socket socket; public User(Socket socket) { //creates a stream for the socket that the user connected with this.socket = socket; initStream(); } public void initStream() { //inits streams after socket is initiated (through ss.accept()) try { out = new DataOutputStream(socket.getOutputStream()); in = new DataInputStream(socket.getInputStream()); }catch(IOException e) { e.printStackTrace(); } } public void closeStream() throws IOException { //throws exception since i have a chance to catch it in my run() method out.close(); in.close(); socket.close(); } public void sendMessage(String string) { try { out.writeUTF(string); }catch(IOException e) { e.printStackTrace(); } } public void run() { //when thread starts, accept/handle data String input; try { while((input = in.readUTF()) != null) { //handle input } closeStream(); }catch(IOException e) { e.printStackTrace(); } } } </code></pre> <p><code>in.readLine()</code> is depreciated, which means it's out-dated and shouldn't be used (to avoid bugs). Now that you have your User class set up, which handles the data, you can now create a new User each time a connection is received.</p> <pre><code>public class Server() { public static ArrayList<User> userlist; public static synchronized void stop() { //synchronized in-case another thread other than the main thread stops the server if(!running) return; running = false; } public static void main(String[] args) { /* uses the JVM thread (main thread for applications), so if you dont wanna ** dedicate your entire server to accepting connections only (since Users are in new thread) ** create a new thread for the code in this void method. */ try { ServerSocket ss = new ServerSocket(8000); userlist = new ArrayList<User>(); User user; //holds the user so we can put it in the list, then start while(running) { user = new User(ss.accept()); list.add(user); user.start(); } }catch(IOException e) { e.printStackTrace(); } } } </code></pre> <p>Hopefully, that'll give you a better idea for how your server should run.</p> <p>As for your client.. Well, there are a ton of things you should realize:</p> <p>First, big problem, you're re-initializing your DataOutputStream each loop, which is gonna cause the stream server-side to close. Gotta take it out of the loop, possibly put it before (or look at my server example for a better idea of handling stream initialization).</p> <p>Second, the names should be kept on the Server, rather than the Client. This way, its easy to iterate through the names, check if its taken, ect..</p> <p>Third, nothing with networking, but seeing how you never refer to <code>Thread n</code> or <code>Thread input</code>, other than to start it, you should remove the reference variable. (even though im pretty sure local vars are picked up by the Garbage Collector, still looks nicer). Example:</p> <pre><code>public void method() { new Thread(new Runnable() { public void run() { //code } }).start(); new Thread(new Runnable() { //run method }).start(); } </code></pre> <p>Hope this helps you understand how a multi-threaded server works! :)</p> <p>PS: This is a very basic server, and really shouldn't be used for large scale applications. Creating new threads (new User()) can cause a lot of overhead, so its best to handle connections using an ExecutorService, or some other type of threadpool service. Good luck!</p>

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