Controlling "CMD.EXE" via Process - Never ends?

Question

I'm trying to write a Java program that parses a text file & executes various command promt commands (I'm trying to keep it platform independant, because I know Lin/Un/nix users who would find this userful as well). I found a small tutorial on the web which gave an example of:
Process p = Runtime.getRuntime().exec("<YOUR COMMAND HERE>");
BufferedReader stdInput = new BufferedReader(new InputStreamReader(p.getInputStream()));
BufferedWriter stdOutput = new BufferedWriter(new OutputStreamWriter(p.getOutputStream()));
BufferedReader stdErr = new BufferedReader(new InputStreamReader(p.getInputStream()));
Now; I have inserted "cmd.exe" for <YOUR COMMAND HERE>. If I write a command out to stdOutput, the first command executes, but not subsequent ones. Small segment looks like:
while (line != null) {
stdOutput.write("mkdir \"" + new_folder + "\"\n");
stdOutput.flush();
line = file_reader.readLine();
This is an abridged version of my ode, but thats the problem. I get the first folder created, the process never terminates and I've tried emptying out the stdInput & stdErr bufferes, but it still won't execute subsequent commands issued to stdOutput.
Can someone help me? I'd rather not write this all to a .BAT/.sh file :(

Answer 1

I am quite perplexed now! I have just tried the following code on my PC, and have ended up with the most annoying two folders under my C:\ drive!
import java.io.*;
public class Cmd {
    public static void main(String[] args) {
        try {
            Process p = Runtime.getRuntime().exec("cmd.exe");
            BufferedReader stdInput = new BufferedReader(new InputStreamReader(p.getInputStream()));
            BufferedWriter stdOutput = new BufferedWriter(new OutputStreamWriter(p.getOutputStream()));
            BufferedReader stdErr = new BufferedReader(new InputStreamReader(p.getInputStream()));
//            System.out.println(stdInput.readLine());
//            System.out.println(stdInput.readLine());
//            System.out.println(stdInput.readLine());
            stdOutput.write("mkdir \"c:\\folder1\"\n");
            stdOutput.flush();
//            System.out.println(stdInput.readLine());
            stdOutput.write("mkdir \"c:\\folder2\"\n");
            stdOutput.flush();
//            System.out.println(stdInput.readLine());
        } catch (IOException e) {
            e.printStackTrace();
Perlexion over! Since you had your code in a loop I tried the same. I saw that in a loop creating 10 folders, the code created only two. See below the code that fixed this problem:
import java.io.*;
public class Cmd {
    public static void main(String[] args) {
        try {
            Process p = Runtime.getRuntime().exec("cmd.exe");
            BufferedReader stdInput = new BufferedReader(new InputStreamReader(p.getInputStream()));
            BufferedWriter stdOutput = new BufferedWriter(new OutputStreamWriter(p.getOutputStream()));
            BufferedReader stdErr = new BufferedReader(new InputStreamReader(p.getInputStream()));
            System.out.println(stdInput.readLine());
            System.out.println(stdInput.readLine());
            System.out.println(stdInput.readLine());
            stdOutput.write("mkdir \"c:\\folder1\"\n");
            stdOutput.flush();
            System.out.println(stdInput.readLine());
            stdOutput.write("mkdir \"c:\\folder2\"\n");
            stdOutput.flush();
            System.out.println(stdInput.readLine());
        } catch (IOException e) {
            e.printStackTrace();
}Commenting out different combinations of System.outs gives different results.
In summary: it is important that you match the correct number of output lines from the CMD.EXE output stream with readLines.
I didn't like how the wording came out, but you get the gist.
HTH,
Manuel Amago.