Getting the Output Stream of a Process without exec()ing it first.

Question

Hi there,
I am writing a java application which needs to open another application "gnuplot". Now my operating system is windows and I open pgnuplot .
Also I want to send input to the above gnuplot (say plot sin(x) ) via the outputStream. The following is what I do :-
     String gnuplot_cmd = "plot sin(x)\n" ;
          Process p = Runtime.getRuntime().exec("C:/gnuplot/gnuplot4/bin/pgnuplot.exe");
          PrintWriter gp = new PrintWriter(p.getOutputStream());
          gp.print(gnuplot_cmd);
          gp.close();
But the above doesn't work fully , in that only the blank wgnuplot terminal window pops up however I am unable to direct input to the gnuplot application.
The reason being that , pgnuplot checks for
its stdin being redirected the moment it's started. If, at that time,
the "PrintWriter" is not yet connected to the OutputStream of the
process, that check will fail, and pgnuplot will revert to just executing
wgnuplot, without any command line redirection.
I am facing a problem of how to attach a OutputStream to the process, without getting exec()ing the process.
Is there anyway at all, i can get a process without starting it, so that I can attach an output Stream to it before it gets executed?
I am open to work arounds, anything that will automate the process of writing to the gnuplot terminal.
thanks!
nandita.

Answer 1

The reason being that , pgnuplot checks for
its stdin being redirected the moment it's started.
If, at that time,
the "PrintWriter" is not yet connected to the
OutputStream of the
process, that check will fail, and pgnuplot will
revert to just executing
wgnuplot, without any command line redirection. I'm not convinced this analysis is correct. gnuplot doesn't need to know that there's a PrintWriter there, and it probably can't know. It just needs to know whether its standard input is coming from console or not. The Java library code that can invoke processes probably handles the redirect right away, and that's why there's the OutputStream available even before you create the PrintWriter.
exec can be tricky. I think the problem may be that you're not dealing with standard output or standard error. Read this:
When Runtime Exec Won't
If that still doesn't help, there may be options to gnuplot to tell it exactly where its input is coming from.