是否有适当的方法来检测和处理突然断开连接的服务器

Question

I'm using this code to detect if a server isn't connect

    private boolean isServerListening() {

    try {
        s = new Socket("localhost", PORT);
        return true;
    } catch (IOException e) {
        System.out.println(e);
        return false;
    }
}

and Thread to handle suddenly disconnected server

    Thread checkServer = new Thread(() -> {
        while (true) {
            if (isServerListening()==false) {
                JOptionPane.showMessageDialog(null, "Server is disconnected!");
                System.exit(0);
            }
        }
    });

The problem is:

1. I think the method took too much time (about 4 seconds) to execute and return.So is there a proper way?
2. No matter the server is connected or not, this Thread still show the JOptionPane and terminate my program.Am I wrong at some point?

Answer 1

There is no general solution that fits all. Bsically there are different types of "lost connection":

1. Your computer disconnects, so it knows immediatley that the connection is closed.
2. The other side disconnects, it might happen that this signal does not reach your computer, so it will still think that you are connected.
3. The physical connection breaks, both sides cannot inform the other side.

The Socket has the methods isConnected() and isClosed() which you should use.

The only way to check a connection surely is by sending a message and receiving an answer. Then it might take up to 60 seconds (by default) until your computer notices the lost connection.