Question

I’m writing a basic Server-client program in Java and I’m trying to handle the case where the client terminates unexpectedly.

public void run() {
    while(alive) {
        try {
            // socketIn is a BufferedReader wrapped around the socket's InputStream.
            String input = socketIn.readLine();
            if(input == null)
                continue;
            String response = processInput(input);
            // socketOut is a PrintWriter wrapped around the socket's OutputStream.
            if(response != null) {
                socketOut.println(response);
                socketOut.flush();
            }
        } catch(IOException e) {
            System.out.println("TRACE 1");
            alive = false;
        }
    }
    System.out.println("TRACE 2");
}

But when I kill the client, the loop keeps going and neither TRACE is printed out. I’m assuming that when a socket is closed from the other end and I am trying to read from it, it will throw an IOException.

Was this a bad assumption? What can I do to fix this?

Answer 1

readLine() will return null at end of stream, which is what happens when the remote end closes the connection normally. You are attempting to continue on this condition, which will loop forever. IOException will be thrown if the connection is broken abnormally.