Question

Basically I want to create a rock solid server.

while (keepRunning.get()) {
    try {
        Socket clientSocket = serverSocket.accept();

        ... spawn a new thread to handle the client ...
    } catch (IOException e) {
        e.printStackTrace();
        // NOW WHAT?
    }
}

In the IOException block, what to do? Is the Server socket at fault so it need to be recreated? For example wait a few seconds and then

serverSocket = ServerSocketFactory.getDefault().createServerSocket(MY_PORT);

However if the server socket is still OK, then it is a pity to close it and kill all previously accepted connections that are still communicating.

EDIT: After some answers, here my attempt to deal with the IOException. Would the implementation be guaranteeing keeping the server up and only re-create server socket when only necessary?

while (keepRunning.get()) {
    try {
        Socket clientSocket = serverSocket.accept();

        ... spawn a new thread to handle the client ...
        bindExceptionCounter = 0;
    } catch (IOException e) {
        e.printStackTrace();

        recreateServerSocket();
    }
}

private void recreateServerSocket() {
    while (keepRunning) {
        try {
            logger.info("Try to re-create Server Socket");
            ServerSocket socket = ServerSocketFactory.getDefault().createServerSocket(RateTableServer.RATE_EVENT_SERVER_PORT);

            // No exception thrown, then use the new socket.
            serverSocket = socket;
            break;
        } catch (BindException e) {
            logger.info("BindException indicates that the server socket is still good.", e);
            bindExceptionCounter++;

            if (bindExceptionCounter < 5) {
                break;
            }
        } catch (IOException e) {
            logger.warn("Problem to re-create Server Socket", e);
            e.printStackTrace();

            try {
                Thread.sleep(30000);
            } catch (InterruptedException ie) {
                logger.warn(ie);
            }
        }
    }
}    

Answer 1

If in doubt, you could try re-creating the server socket, using the same port. If the socket has been closed, then the creation will succeed and you can continue processing new connections. The old connections are gone, but that’s outside of your control since the socket was closed. If the socket was not closed, then creating a new instance will fail since the port is still in use, which you can just ignore – i.e. don’t replace the current server socket reference.

In general, clients should also assume that connections will be broken and that reconnection is necessary. In other words, it’s not just the server that has to be robust – clients should also anticipate connection errors and reconnect.