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Java Forum / General / June 2005Read keys without keyboard focus
I have an non-gui application that is running in the background. I want to be able stop this when I press <ESC> key (or any other key). The only way I can think of is to get to the OS queue for the keyboard! Is there any other way? Can Java do this? I already know that java can access "private" OS resources in java.awt.Robot. But a robout cannot read the keyboard... > I have an non-gui application that is running in the background. I want > to be able stop this when I press <ESC> key (or any other key). The > only way I can think of is to get to the OS queue for the keyboard! Is > there any other way? Forget about the key-reading junk. A process which runs in the background is not meant to communicate with a console and is usually not attached to one. Send a SIGTERM to the JVM, assuming the VM was *not* started with the -Xrs options (http://java.sun.com/j2se/1.5.0/docs/tooldocs/solaris/java.html#Xrs). If it was, then you need a SIGKILL. But that doesn't give the JVM and your application any chance of an orderly shutdown. /Thomas  SignatureThe comp.lang.java.gui FAQ: ftp://ftp.cs.uu.nl/pub/NEWS.ANSWERS/computer-lang/java/gui/faq Of course most programs are not attached to a consol and they talk to the keyboard just fine. Whether my non-gui application should or should not receive inputs from keyboard is none-of-...Oh well, let's be nice,...lets just say that in my case it really makes sense to have no windows and still listen to the keyboard. Since my problem came up, I have done some reading about signals. They are useless because they are so antiquated. Signals probably made sense in a UNIX like environment 20 years ago when the idea of socket and thread was not within the reach of a typical C program. Here is the solution that I came up with that solved my problem. Unfortunately, it is not a pure java solution. Although, it could be made into one, if SUN introduced an OS specific class (java.awt.KeyboardInterceptor, perhaps?) similar to other peered classes. My idea is very simple. Write an OS specific program that sends a copy of all keys pressed to a (host/port) -- non-blocking write (If SUN volunteers, this would be the part that they write for all supported OS's.) In your java program (or any other program) have a thread that listens to that (port) and communicates with other threads. Done! Conceivably, the KeyboardInterceptor class (the native program) could be made more elaborate by sending certain key sequences to certain host/port. So in this scenario, you would register a set of key bindings to a host/port with KeyboardInterceptor and then you don't have to listen to all keys...beats the hell outta signals--which ar OS specific anyway. Nay? > have to listen to all keys...beats the hell outta signals--which ar OS > specific anyway. Nay? Are you asking me? Since you just told me to shut up I guess you have to find someone else to discuss your bright ideas. /Thomas SignatureThe comp.lang.java.gui FAQ: ftp://ftp.cs.uu.nl/pub/NEWS.ANSWERS/computer-lang/java/gui/faq A: I have a problem... B: Your problem has no solution since it's not in the FAQ. A: But it does! Here is an idea... B: Don't talk back to me... A: (somewhat surprised)...Well, of course! javaplus@hotmail.com wrote in comp.lang.java.programmer: > A: I have a problem... > B: Your problem has no solution since it's not in the FAQ. > A: But it does! Here is an idea... > B: Don't talk back to me... > A: (somewhat surprised)...Well, of course! Keep talking. Somebody might still think that you are a smart person. SignatureAntti S. Brax Rullalautailu pitää lapset poissa ladulta http://www.iki.fi/asb/ http://www.cs.helsinki.fi/u/abrax/hlb/ [1385 messages expunged from folder "Spam"] Lol, this is really funny. And to whom would I be shownig off in an anonymous post? Keep trolling buddy, better luck next time! Trying to get past the flames for a moment - I'm just finishing up on an NIO war - the non-standard but somewhat available C function kbhit() does what you seemingly describe, but the JDK itself has no similair functionality. This issue was filed as a bug report 8 years ago to sun and is worth a read for the comments and work arounds. http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4050435 Don't give up Signals so easily, here's an article that shows a nice chart between the OS's and how to use signals in Java. http://www-106.ibm.com/developerworks/ibm/library/i-signalhandling/ HTH, iksrazal http://www.braziloutsource.com/ Yeah, a kbhit() would solve the problem and it is a better idea than what I had described because it is simpler. In fact, what I had described can be build from kbhit(). I had read the IBM article before and that was my main reason to think of signals as "outdated". If I'm not mistaken, the article describes in great detail that they are not only OS dependent, but also JVM dependent! Thanks for the bug report reference; I was not aware of it. But of course, this is a fundamental problem and I'm not surprised that it has so many votes. In fact, I'm putting my vote for this update too. As many have noted this is only a few lines of JNI that should really be provided by SUN. I feel that this problem does not deserve as much time as I've put into it. I mean, I prefer to be working on my application rather than "patching up" holes in java--just a question of productivity, IMHO. I'm not actively pursuing this problem anymore. But thinking about it a bit more, neither kbhit() function nor the bug report referenced before is really much related to this problem (although it is nice to have them in Java). Signals are really not relevant either. In all those cases, the issue is related to when you do have the keyboard focus. When you don't have the keyboard focus and still want to read the keys, then you really need to intercept the OS. At least in the windoz family of OS's this is not too difficult with a "hook" to the keyboard... Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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