How to read process builder input and error streams?

Question

I tried to read a process'es std out and error using the solutions in How to redirect Process Builder's output to a string?, but it does not output anything.

Shouldn't there be a way to attach a stream reader to the process builder before starting the process?

/*
private String getInputAsString(InputStream is)
{
   try(java.util.Scanner s = new java.util.Scanner(is)) 
   { 
       return s.useDelimiter("\\A").hasNext() ? s.next() : ""; 
   }
}
*/


private static BufferedReader getOutput(Process p) {
    return new BufferedReader(new InputStreamReader(p.getInputStream()));
}

private static BufferedReader getError(Process p) {
    return new BufferedReader(new InputStreamReader(p.getErrorStream()));
}


            List<String> args = new ArrayList<String>();
            args.add ("cmd"); // command name
            args.add ("/c");
            args.add ("start");
            args.add (fileName);
            ProcessBuilder pb = new ProcessBuilder (args);
            pb.directory(new File(Support.getJustThePathFromFile(file)));
            Map<String, String> envs = pb.environment();
            String path = envs.get("Path");
            envs.put("Path", Paths.get(".").toAbsolutePath().normalize().toString() + ";" +path);


            //pb.redirectOutput(new Redirect() {});
            Process p = pb.start();

            //String stdOut = getInputAsString(p.getInputStream());
            //String stdErr = getInputAsString(p.getErrorStream());
            //System.err.println("stdOut=" + stdOut);
            //System.err.println("stdErr=" + stdErr);
            try
            {
                p.waitFor();

                BufferedReader output = getOutput(p);
                BufferedReader error = getError(p);
                String ligne = "";

                while ((ligne = output.readLine()) != null) {
                    System.out.println(ligne);
                }

                while ((ligne = error.readLine()) != null) {
                 System.out.println(ligne);
                }

            }
            catch (InterruptedException e)
            {
                e.printStackTrace();
            }