Thread: How to redirect System.out to command line window

As I'm running Linux at the moment, I can't test anything. That said, my assumption would be to try something like:

public static void main(String args[]) {
	final String[] params = {"cmd.exe", "/C", "\"start; cd c:\\\""};
 
	try {
		Process process = Runtime.getRuntime().exec(params);
		System.setOut(process.getOutputStream());
		System.setIn(process.getInputStream());
	} catch (IOException e) {
		e.printStackTrace();
	}
}

As it should be obvious from my opening statement however, this sort of Java code will no longer be interoperable between all operating systems.

Okay, how about .setOut(new PrintStream(getStream))?

But process is just a Process object, isn't it? Which would mean that it does not necessarily "know" a console window exists. I could be wrong, but I believe the process.getOutputStream() and process.getInputStream() methods get the input and output streams of the Process itself, not of the console the process created... In fact, I don't even know if you can get the console that was created.

While the Process is alive, the hooks to both streams do refer to opened process. In the past, I've used the input streams to read values returned by .exe files.

--- Update ---

Originally Posted by Cornix

Did that too, since the "setOut" method needs a printStream. You can not just set it to the output stream returned by process.getOutputStream().

setOut(process.getOutputStream()) would work directly, but my thinking was to test it while it was wrapped in a new stream. But obviously that did not work either.

Fair doos.

Two things:
1. I believe the streams coming from the Process object are not ones you can add to, so you would not be able to append the System.out to the stream
2. The "output" (meaning what a command line would print out while running a command) for a Process object is actually obtained with Process.getInputStream(). Quoted from the api:

public abstract OutputStream getOutputStream()
...

Returns:
the output stream connected to the normal input of the subprocess.

...
public abstract InputStream getInputStream()
...
Returns:
the input stream connected to the normal output of the subprocess.

Ok. So your entire goal here is to just make a console window pop up when you double click the jar, correct?
I'm not sure if you can do that without requiring the user to modify the default executing command for the jar (jars, by default, run without the command prompt). I would think there would HAVE to be a way to create a Console object, but I have no idea how.

I've got a weird but plausable approach for you! I found one of my earliest Swing applications from University a few years back which simulates a command prompt in Swing. Its appearance can be seen in the picture below, and although it has very limited functionality and is probably built on a terrible code base, it could work
WXUXtlt.jpg

All the extra code you would need is:

	public static void main(String[] args) {
		ConsoleWindow console = new ConsoleWindow();
		console.setVisible(true);
		JScanner scanner = console.getScanner();
 
		System.out.println("Please Enter Your Name: ");
		scanner.nextLine();
	}

where you use the JScanner instead of a traditional Scanner. All functions for the JScanner are replicated, so its API is practically identical if i remember rightly.
If you do fancy trying it out, heres the jar: https://www.dropbox.com/s/x7pfxsgrks...ingConsole.jar

Did you already attach the System.in and out streams to the console?

If that was directed at me, i think it was done using System.setOut(new PrintStream()) etc but using PipedOutputStream and an extra thread. The inputstream element was never added, as it simply comes from the JTextField.

Well, the "simple" way is to change your run configurations for that specific jar, but that has to be independently done by each user on their individual operations systems, which no one wants to try to explain to an end-user...

The issue stems from there being two different executable vms for java. One of them: javaw.exe (I think this one) does not have a console. The other one: java.exe does have a console. By default, jars are assumed to be "window apps", so they run with javaw.exe. You can right-click the jar, go to run-as, and find the java.exe one, and it should open a console, but 99% of users would never do that (they would just double-click).

If you just wanted an easier way for end users to run your app without typing into cmd (instead of needing 2 windows), just ship an executable batch file with your jar.