Is there a way to determine if Java System.in is “interactive”?

Question

If the input is interactive, i.e. from the console, I want to print a command prompt e.g. \">\"

But if it is redirected e.g. from a file, then I do not want to promp

Answer 1

AFAIK, there is no way to do this in pure Java, and even doing it in JNI / JNA would be complicated.

An alternative might be to use the new Console API introduced in JDK 1.6. This allows you to try to get a reader/writer for the console. If it succeeds, the result is guaranteed to be interactive ... in the sense that you mean.

A second alternative would be to check do the legwork in the wrapper script that you use to launch your application, and pass the information to Java via the system properties. For instance, on a GNU/Linux system the tty(1) command can be used to tell if stdin is a connected to a "tty" device.