Java：为什么在Java / Groovy中运行命令时此命令的输入错误

Question

The code is:

Process p = "java -Xmx128M -version".execute()
Process p = "ls\ndir".execute()
p.inputStream.eachLine { println it}
println "error:"
p.errorStream.eachLine { println it}

then it print: error:

java version "1.6.0_23"
Java(TM) SE Runtime Environment (build 1.6.0_23-b05)
Java HotSpot(TM) Client VM (build 19.0-b09, mixed mode)

Why the output is in the errorStream, not the inputStream?

Answer 1

I agree that it's not an error to ask java to print its version, but it's just the decision they made from the beginning. I think most applications print version to stdout, but at least a few print it to stderr; eg python and gcc seem to print to stderr, ruby prints to stdout.

It doesn't seem likely that they will change it, since a bug report got this reply (in 2001):

We should think very, very carefully before ever fixing this bug. It's obviously the wrong thing to print version information to stderr, but since we've been doing that since the beginning of time it seems likely that we'll break existing systems built on top of Java if we change it now.

So they acknowledge that it's probably the wrong thing to do, but won't change it. The bug is marked with "won't fix".