服务器不适用于多个连接

Question

我有一个可以正常工作的简单客户端-服务器应用程序。问题是它只适用于一个启动的客户端，但不适用于两个或更多。它建立连接，但是当您尝试在第一或第二输入文本时，服务器会中断。我认为问题可能出在 Server.java.

中的函数 broadcast()

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();
            }
        }
    }

}

当打开两个Client.java并连接到server.java时一切正常。但是当我尝试从这两个打开的客户端服务器 returns 发送一些消息时，这些错误：

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

发生的事情是您的代码从客户端扫描第一行（"sds"，打印到标准输出），然后循环返回并立即尝试从客户端扫描下一行。由于客户端还没有发送任何东西，输入流扫描器抛出异常。

Answer 2

NewClient class 是一个内部 class。此 class 的所有实例都是使用外部 class 的相同实例创建的。更改代码将解决问题：

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);
            }
        }

服务器不适用于多个连接

Server doesn't work with more than one connection

java

multithreading

client-server