Question

I have this client, the server information is not important. The output of this code is very random.

class Client {
    public static void main(String args[]) throws Exception

    {
        BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));
        Socket clientSocket = new Socket("127.0.0.1", 10004);//this will become the addr of the server you want to input.
        InetAddress host = clientSocket.getInetAddress();
        //      System.out.println(host);

        DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
        BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        boolean exit = false;

        while (!exit) {
            while (inFromServer.ready()) {
                System.out.println(inFromServer.readLine());
            }
            String sentence = inFromUser.readLine();
            outToServer.writeBytes(sentence + "\n");
        }
        clientSocket.close();
    }
}

If I run this in debug mode, it has always the correct result. E.g.

• please insert password
• the user types pass
• pass correct
• please type command
• and you type command
• etc
• etc

When it’s not in debug mode, all goes wrong. I don’t even get the initial request from server. What is going on? I think the read line might be executed too fast?

Answer 1

in.ready() does not wait for any data to be available. It the server hasn’t sent the data yet when you client reads that line, you’re going to skip the readLine() completely.

Just remove that while and do a plain readLine().

If there are phases where you need to wait for multiple lines from the server, you’ll need to implement more logic. Usually, the server will send an “end of message” marker to signify to the client that it is done. For example, when the server is done, it could send the message “END-OF-MESSAGE”. In the client code, you would do:

boolean serverDone = false;
while (!serverDone) {
  String message = in.readLine();
  if (message == null) {
    // handle this problem: the server has closed the connection
    serverDone = true; // or return, or throw
  } else if ("END-OF-MESSAGE".equals(message)) {
    serverDone = true;
  }
}