Write and read data from console at run time in java program

Question

I have one shell script which has some commands, one of which command is expecting to enter some data at runtime. I am running this shell script using exec() method. Currently I am entering data manually if it asks to enter. Following is my code,

            Process p = Runtime.getRuntime().exec("myshellscript");

            BufferedReader stdInput = new BufferedReader(new InputStreamReader(p.getInputStream()));

            BufferedReader stdError = new BufferedReader(new InputStreamReader(p.getErrorStream()));

            // read the output from the command
            System.out.println("Here is the standard output of the command:\n");
            while ((s = stdInput.readLine()) != null) {
                System.out.println(s);
            }

           // read any errors from the attempted command
            System.out.println("Here is the standard error of the command (if any):\n");
            while ((s = stdError.readLine()) != null) {
                System.out.println(s);
            }

            System.exit(0);

What I want to do is whenever console expect's data to be entered, it should be entered by java program and just continue my further java program.

Maurice Perry · Accepted Answer · 2016-11-29 06:23:55Z

2

Here's what I do:

create two threads that will read from p.getInputStream() and p.getErrorStream(),
write the data in p.getOutputStream(),
wait for the two thread to terminate (with the join() method)

EDIT:

public class Main {
    private static final Logger LOG = Logger.getLogger(Main.class.getName());

    public static void main(String[] args) {
        try {
            Process p = Runtime.getRuntime().exec("myshellscript");
            Thread outHandler = new OutputHandler(p.getInputStream(), "UTF-8");
            outHandler.setDaemon(true);
            outHandler.start();
            Thread errHandler = new OutputHandler(p.getErrorStream(), "UTF-8");
            errHandler.setDaemon(true);
            errHandler.start();
            sendInput(p, "the input data", "UTF-8");
            int result = p.waitFor();
            outHandler.join();
            errHandler.join();
            System.out.println("exit code: " + result);
        } catch (IOException ex) {
            LOG.log(Level.SEVERE, null, ex);
        } catch (InterruptedException ex) {
            LOG.log(Level.SEVERE, null, ex);
        }
    }    

private void sendInput(Process process, String input, String encoding)
        throws IOException {

    try (OutputStream stream = process.getOutputStream();
            Writer writer = new OutputStreamWriter(
                    stream, encoding == null ? "UTF-8" : encoding);
            PrintWriter out = new PrintWriter(writer)) {
        if (input != null) {
            Reader reader = new StringReader(input);
            BufferedReader in = new BufferedReader(reader);
            String line = in.readLine();
            while (line != null) {
                out.println(line);
                line = in.readLine();
            }
        }
    }
}

    private static class OutputHandler extends Thread {
        private BufferedReader in;

        private OutputHandler(InputStream in, String encoding)
                throws UnsupportedEncodingException {
            this.in = new BufferedReader(new InputStreamReader(
                    in, encoding == null ? "UTF-8" : encoding));
        }

        @Override
        public void run() {
            try {
                String s = in.readLine();
                while (s != null) {
                    System.out.println(s);
                    s = in.readLine();
                }
            } catch (IOException ex) {
                LOG.log(Level.SEVERE, null, ex);
            } finally {
                try {
                    in.close();
                } catch (IOException ex) {
                    LOG.log(Level.SEVERE, null, ex);
                }
            }
        }
    }
}

edited Nov 29, 2016 at 6:23

answered Nov 29, 2016 at 5:49

Maurice Perry

9,6782 gold badges15 silver badges28 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Tushar Deshpande Over a year ago

can you please brief the code I am new to java, I never worked on multithreading.

Maurice Perry Over a year ago

Note that if you were using a ProcessBuilder, you could do redirectErrorStream(true) and you would need only one thread.

Maurice Perry Over a year ago

Added method sendInput

Tushar Deshpande Over a year ago

Thank you so much for your wonderful help Maurice Perry, I was struggling on it for long time now it worked.

Collectives™ on Stack Overflow

Write and read data from console at run time in java program

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related