Java keyboard input parsing in a console app

Question

I've just started messing around with JLine to parse character input in console mode. It seems to work well, but I'm wondering:

Is there a nonblocking way in JLine to find out if characters are available? (i.e. like kbhit() in Windows.)

I suppose I could always wrap keyboard input in its own thread which then offers the keyboard characters in a thread-safe queue to the main thread, but that seems like it should be unnecessary.

EDIT: This is character-by-character parsing. I am not going to use a GUI. The usual InputStream I/O in Java in console mode requires you to hit the Enter key first (e.g. it's buffered input only). Please don't tell me character-by-character input in console mode is impossible in Java; it isn't. JLine does it using a portable interface with a platform-dependent implementation.

Edit update: I was able to hack together a helper class to do the blocking I/O in a worker thread (using JLine for the per-character I/O, warning: you have to parse Ctrl-C yourself!) & then communicate via a synchronized queue with an isempty() routine. For what I'm doing right now that's fine, but I would really like to know a Good Way To Do This In The Future.

Answer 1

You can't use a console to get non-blocking input without native libraries.

You'll have to write a Swing app and write a KeyListener

Read this tutorial: http://java.sun.com/docs/books/tutorial/uiswing/events/keylistener.html

Answer 2

I don't know about JLine, but input to a java console app is not difficult. The following code waits for input from the command line then prints out what you just typed. (after you hit enter)

import java.io.*;
public class Test {
    public static void main (String [] args) throws IOException {
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            String input = br.readLine();
            System.out.println(input);
    }
}

Then you can parse the input String.

Ok I understand what you are asking now. I haven't tested it but looking though the 1.6 API this may work.

Console con = System.console();
Reader r = con.reader();

Reader has a method read() to read in a single character, it will still block but only for one character, so you could read in a character do you want you need to do then go back again and wait for the next character input.

Answer 3

You seem to be on the right track.

I think the "right" way to do this is a worker thread that pours all the blocking I/O into a non-blocking queue. Hava a look at ConcurrentLinkedQueue from java.util.concurrent.