How to make an input to a started process with ProcessBuilder?

Question

We have a closed-source archive that does only one thing: reads a string input and outs its value hashed. Not by its command arguments, but once it is started and stays continuously open, getting inputs and giving the value properly hashed.

So I want to open it with ProcessBuilder and do the inputs. The problem is that i have tried to input in the process and i have failed:

ProcessBuilder pb = new ProcessBuilder("/path/to/executable");
Process p = pb.start();
OutputStream os = p.getOutputStream();
PrintWriter pw = new PrintWriter(os);
pw.write("Hey\n");
String result = read(p);
System.out.println("Out: " + result);
p.destroy();

But looks like i'm not getting any output, first of because the executable is not getting my "Hey".

So the main question is, how do I input into the started program? Any kind of suggestions are welcome.

Answer 1

After

pw.write("Hey\n");

Try doing a

pw.flush();