Java while（true）循环运行一次

Question

I am writing a Server-Multiclient communication application, and I need to make a Thread that loops and accepts clients. My current code is:

Thread acceptor = new Thread() {
    public void run() {
        while(true){
            System.out.println("looking for clients");
            try{
                Socket s = serverSocket.accept();
                    clientList.add(new ConnectionToClient(s));
                }
                catch(IOException e){ e.printStackTrace(); }
            }
        }
    }
};
acceptor.setDaemon(true);
acceptor.start();

However, when I run my application, the text looking for clients only appears one time, and no clients can connect.

I don't understand why my while(true) loop isn't actually looping, and only running once.

EDIT:

The ConnectionToClient constructor is:

ConnectionToClient(Socket socket) throws IOException {
    this.socket = socket;
    in = new ObjectInputStream(socket.getInputStream());
    out = new ObjectOutputStream(socket.getOutputStream());

    Thread read = new Thread(){
        public void run(){
            while(true){
                try {
                    Object obj = in.readObject();
                    messages.put(obj);
                } catch(IOException | ClassNotFoundException | InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    };
    read.start();
 }

Answer 1

You're calling acceptor.setDaemon(true); .

Its Javadoc explains:

Marks this thread as either a daemon thread or a user thread. The Java Virtual Machine exits when the only threads running are all daemon threads.

So you're marking your only running thread as a daemon thread (since your main thread ends when the main method ends). You're lucky that you got one iteration of the loop, since your VM almost immediately exits as there are no more non-daemon threads.

Solution: remove the line that reads acceptor.setDaemon(true);

---

Your updated post shows the other problem, the constructor ConnectionToClient(Socket socket) inadvertently tries to read from the Socket , which blocks the acceptor thread until the client sends data.

The problem is the constructor of ObjectInputStream tries to read the header of the object stream.

Therefor, you should move the construction of the ObjectInputStream and ObjectOutputStream into the read Thread, so that this doesn't block the acceptor Thread.

Answer 2

Ok, thanks to @ErwinBolwidt.

The problems were:

1) The .setDaemon(true) was causing problems.

2) Creating the ObjectInputStream before the client was connected was reading the header that needed to be sent to the server, and blocking the client from sending it to the server. Moving that to the read thread allowed the client to actually connect to the server.

Thanks again @ErwinBolwidt.