input and ouput problem with BufferedReader/Writer to external process

[Chris Dancy]

Here is the issue. java program starts and launches an external program. I get the inputstream and outputstream of that process to play with. I can pipe all the inputstream information to a textarea just fine however... its when i want to give input to the outputstream that the problem occurs. I believe I'm just thinking of this the wrong way and am coming here for help.
Also if anyone looking at this code can knows how I can differentiate from a process that needs input to one that does not that would be great as well.

here is the sample code and the following ruby script I used for the external program...

 
public static void test3() throws IOException{
String line;
Scanner scan = new Scanner(System.in);

    Process process = Runtime.getRuntime ().exec ("/home/cdancy/Desktop/start.rb");
    OutputStream stdin = process.getOutputStream ();
    InputStream  stderr = process.getErrorStream ();
    InputStream  stdout = process.getInputStream ();
    
    BufferedReader reader = new BufferedReader (new InputStreamReader(stdout));
    BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(stdin));
    
    String temp = "\n";
    writer.write(temp);
    writer.close();
    System.out.println("before loop");
    while ((line = reader.readLine ()) != null) {
    
        System.out.println ("Stdout: " + line);
        String input = scan.nextLine();
        input += "\n"; 
        writer = new BufferedWriter(new OutputStreamWriter(stdin));
        writer.write(input);
    writer.close();
    }
    reader.close();
}

here is the simple ruby script i am using...

#! /usr/bin/ruby
puts "Enter a number: "
line = gets
puts "Number is " + line
puts "Enter another number: "
line = gets
puts "Second number is " + line
puts "Script is done"

again any help is appreciated.

Thanks in advance,

Christopher Dancy
[ December 30, 2008: Message edited by: Martijn Verburg ]

[Martijn Verburg]

Hi Chris,

Are you getting any errors? Or are you not seeing your writes executed?

[Chris Dancy]

No errors at all... The code just sits and waits ... The BufferedWriter is blocking for some reason, because if i dont even include it the program simply spits out the lines of the processes output, however when i do include it the program just sits and waits. And it waits at the loop, when a line is trying to be read and will not even continue further into the loop. The point of why im trying to do this is to make a small ide for my senior project and i want to mimic a console/terminal in the bottom pane like most ide's do. I simply cant seem to get this working and i've tried everything at this point. Sorry for getting back to you so late.

[Rob Spoor]

I think you should read When Runtime.exec() won't.