服务器不能与多个连接一起使用

Question

I've got a working simple client-server app. The problem is it works fine just with one started client, but not with two or more. It establish connection, but when you try to enter text in first or second, the server breakes. I think that problem may be at the function broadcast() in Server.java .

Server.java

public class Server {
    final int PORT = 5000;
    private ArrayList<NewClient> al = new ArrayList<NewClient>();
    private Scanner in;
    private PrintWriter out;
    private SimpleDateFormat sdf;
    private int uniqueID = 0;

    private void go(){

        try{
            ServerSocket serverSocket = new ServerSocket(PORT);
            System.out.println("Waiting for clients...");

            while(true) {
                Socket s = serverSocket.accept();
                NewClient chat = new NewClient(s);
                System.out.println("Client number " + chat.getId() + " connected from: " + s.getLocalAddress().getHostName());
                al.add(chat);
                Thread t = new Thread(chat);
                t.start();

            }
        }catch (Exception e) {
            System.out.println("Problem with establishing network connection: ");
            e.printStackTrace();
        }

    }

    public static void main(String[] args) {
        Server server = new Server();
        server.go();
    }

    class NewClient implements Runnable{
        private Socket socket;
        private int id;

        public NewClient(Socket s) {
            this.socket = s;
            this.id = ++uniqueID;
        }
        public int getId() {
            return this.id;
        }

        @Override
        public void run() {
            try{
                in = new Scanner(socket.getInputStream());
                out = new PrintWriter(socket.getOutputStream());
                sdf = new SimpleDateFormat("HH:mm:ss");

                while(true) {
                    String input = in.nextLine();
                    System.out.println("Client said: " + input);
                    broadcast(input);
                }
            }catch (Exception e) {
                e.printStackTrace();
            }

        }
        private void writeMsg(String input) {
            String msg = input + " on " + sdf.format(new Date());
            out.println("You said: " + msg);
            out.flush();
        }

        private void broadcast(String input) {
            for (int i = 0; i < al.size(); i++) {
                NewClient t = al.get(i);
                t.writeMsg(input);
            }

        }
    }

}

Client.java:

public class Client {
    final int PORT = 5000;
    final String HOST = "127.0.0.1";
    private Scanner stdIn;
    private Scanner in;
    private PrintWriter out;


    private void go() {
        setUpNetwork();
    }

    private void setUpNetwork(){
        try{

            Socket s = new Socket(HOST, PORT);
            System.out.println("You are connected to " + HOST);
            NewClient client = new NewClient(s);
            Thread t = new Thread(client);
            t.start();
        } catch (Exception e) {
            System.out.println("Problem with connection to server: " + e);
        }
    }
    public static void main(String[] args) {
        Client client = new Client();
        client.go();
    }

    class NewClient implements Runnable {

        private Socket socket;
        public NewClient(Socket s) {
            this.socket = s;
        }

        @Override
        public void run() {
            try {
                stdIn = new Scanner(System.in);
                in = new Scanner(socket.getInputStream());
                out = new PrintWriter(socket.getOutputStream());

                while(true) {
                    System.out.print("> ");
                    String input = stdIn.nextLine();
                    out.println(input);
                    out.flush();

                    if(in.hasNext()) {
                        System.out.println(in.nextLine());
                    }
                }
            }catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

}

When opens two Client.java and connect it to the server.java everything is ok. But when i try to send some message from this two opened clients server returns these errors:

java.lang.IndexOutOfBoundsException: end
     at java.util.regex.Matcher.region(Matcher.java:1038)
     at java.util.Scanner.findPatternInBuffer(Scanner.java:1010)
Client said: sds
    at java.util.Scanner.findWithinHorizon(Scanner.java:1679)
    at java.util.Scanner.nextLine(Scanner.java:1538)
    at Server$NewClient.run(Server.java:66)
    at java.lang.Thread.run(Thread.java:745)

Answer 1

What's happening is that your code scans the first line from the client ("sds", which is printed to stdout), and then it loops back and immediately tries to scan the next line from the client. Since the client hasn't sent anything more yet, the input stream scanner throws an exception.

Answer 2

The NewClient class is an inner class. All instances of this class are created with the same instance of the outer class. Changing the code will sove the problem:

public NewClient(Socket s) {
            this.socket = s;
            this.id = ++uniqueID;
            try{
                in = new Scanner(socket.getInputStream());
                out = new PrintWriter(socket.getOutputStream());
                sdf = new SimpleDateFormat("HH:mm:ss");
            }catch(Exception e) {
                System.out.println("Exception while creating input/output streams: " + e);
            }
        }