Get output of cmd command from java code

Question

I have a program where I was able to successfully execute cmd commands from my code, but I want to be able to get the output from the cmd command. How can I do that?

Answer 1

You need to the OutputStream (InputStream) of your Process (and you should use a ProcessBuilder)... like so

public static void main(String[] args) {
  String filename = args[1].substring(0, args[1].length() - 5);
  String cmd1 = "javac " + args[1];
  String cmd2 = "java " + filename;

  try {
    // Use a ProcessBuilder
    ProcessBuilder pb = new ProcessBuilder(cmd1);

    Process p = pb.start();
    InputStream is = p.getInputStream();
    BufferedReader br = new BufferedReader(new InputStreamReader(is));
    String line = null;
    while ((line = br.readLine()) != null) {
      System.out.println(line);
    }
    int r = p.waitFor(); // Let the process finish.
    if (r == 0) { // No error
       // run cmd2.
    }
  } catch (Exception e) {
    e.printStackTrace();
  }
}

Answer 2

A general example to get the return from a command would be:

 Process p = null;
    try {
        p = p = r.exec(cmd2);
        p.getOutputStream().close(); // close stdin of child

        InputStream processStdOutput = p.getInputStream();
        Reader r = new InputStreamReader(processStdOutput);
        BufferedReader br = new BufferedReader(r);
        String line;
        while ((line = br.readLine()) != null) {
             //System.out.println(line); // the output is here
        }

        p.waitFor();
    }
    catch (InterruptedException e) {
            ... 
    }
    catch (IOException e){
            ...
    }
    finally{
        if (p != null)
            p.destroy();
    }

Answer 3

look here: Extracting a process's exit code in the case of ThreadInterrupted

You need to get the return code... you must wait for it.