How can I read a single character/key from the console without having to hit Enter? There is an old entry in Sun's bug database claiming that it can't be done in pure java. I've found these approaches
I'd expect to add a single magic-readkey.jar
to my classpath, and to write a few lines of code, like (def just-hit (com.acme.MagicConsole/read-char))
.
Here's an "immediate echo" app using JLine which will print int
s corresponding to registered keypresses, structured as a Leiningen project:
project.clj
:
(defproject con "1.0.0-SNAPSHOT"
:description "FIXME: write"
:main con.core
:dependencies [[org.clojure/clojure "1.1.0"]
[org.clojure/clojure-contrib "1.1.0"]
[jline "0.9.94"]])
src/con/core.clj
:
(ns con.core
(:import jline.Terminal)
(:gen-class))
(defn -main [& args]
(let [term (Terminal/getTerminal)]
(while true
(println (.readCharacter term System/in)))))
The functionality in question is provided by the jline.Terminal
class, which provides a static method getTerminal
returning an instance of a platform-specific subclass which can be used to interact with the terminal. See the Javadoc for more details.
Let's see what asdf
looks like...
$ java -jar con-1.0.0-SNAPSHOT-standalone.jar
97
115
100
102
(C-c still kills the app, of course.)
For anyone who may be reading this in 2015 and beyond, note that more recent versions of JLine no longer have the method Terminal/getTerminal
. I'm sure there is another (possibly better) way to do this now with JLine2, but you can always just use jline "0.9.94"
and the accepted answer will still work, at least up to Clojure 1.6 (of note, you no longer need to require clojure.contrib
).
As an alternative, I would recommend the excellent clojure-lanterna, which is a Clojure wrapper around the Java Lanterna library. As you can see in the docs, there are get-key
and get-key-blocking
functions for reading in single characters of input.
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