Why doesn't the Java console show when using ProcessBuilder?

Question

I use the following to launch a Java application from another Java app.

    ProcessBuilder pb = new ProcessBuilder(javaPath + javaCommand, maxMemStr,
            minMemStr, stackSizeStr, jarCommand, jarfile, jarArg);
    try {
        Process p = pb.start();
    } catch (IOException ex) {
        Logger.getLogger(launch.class.getName()).log(Level.SEVERE, null, ex);
    }

where javaCommand is either java or javaw (javaPath is empty most of the time unless a user points to an alternate path). The problem is, after the app launches, even when I verify the process list to contain java, it doesn't show the console.

Is it because PrcoessBuilder doesn't invoke the command shell? Is there a way to show the console programatically?

Thanks in advance.

Ah, my SO-foo is weak today. Though, I must say, the answers here were more relevant :) — Adam Law
– Adam Law, Commented Jan 22, 2013 at 19:50

CodeBlind · Accepted Answer · 2013-01-22 19:28:17Z

1

This is because the "command console" itself is a process that attaches to the std-in/-out/-err streams of another process and displays them on the screen. When you launch Java all by itself, no other processes will be handling those streams, hence the lack of a command console. To get the results you want, you will need to launch a new instance of the command console and subsequently have it run your custom java command.

There may be a better way to do this... but I think the solution to this is going to be platform-dependent. In Windows, you could do something like:

ProcessBuilder pb = new ProcessBuilder("start", "\"JAwesomeSauce\"", "cmd.exe",
    "/k", javaPath + javaCommand, maxMemStr, minMemStr, stackSizeStr, jarCommand,
    jarfile, jarArg);
try {
    Process p = pb.start();
} catch (IOException ex) {
    Logger.getLogger(launch.class.getName()).log(Level.SEVERE, null, ex);
}

I assume you could do something similar in Linux/Mac if that's the O/S you're using.

answered Jan 22, 2013 at 19:28

CodeBlind

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2 Comments

Adam Law Over a year ago

I was hoping to find a system agnostic solution instead of applying platform specific handling. Is there another way to launch the console apart from getting System.console()? Because in that case, I believe it will return null in my context.

CodeBlind Over a year ago

Yeah, I hear ya... unfortunately, Java's "Platform Independence" is somewhat exaggerated... ;) System.console() returns a console implementation for the JVM you're currently running in. I could be wrong, but I don't believe you can get an actual console object for a separate process, unless you get the input/output/error streams from the Process object you create - but at that point, you'd have to also write your own "Console" implementation because java.io.Console doesn't let you modify its streams.

jdb · Accepted Answer · 2013-01-22 19:30:03Z

1

You may want to run the command like this: cmd /K java ... or cmd /C java ...

answered Jan 22, 2013 at 19:30

jdb

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1 Comment

Adam Law Over a year ago

thanks jdb. I'll definitely try this out and look for its counterparts in other OSes.

Stefan · Accepted Answer · 2013-01-22 19:33:03Z

1

As far as I remember the Processbuilder opens a pipe to a specific process.

Your command window is a process itself with all you see. If you enter commands the cmd/bash usually creates new processes and attaches to them.

answered Jan 22, 2013 at 19:33

Stefan

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2 Comments

Adam Law Over a year ago

thank you Stefan. your advice is similar to what the others here are offering. I appreciate it.

Stefan Over a year ago

yeah, just wanted to through in the pipe keyword for better understanding although all other answers are in their own way all correct.

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