Apache commons exec run interactive terminal application

Question

First of all I'd like to say that I read all the other threads concerning apache commons exec. I have a terminal based executable. When ran, it prompts the user for some input from command line. I need to run this program from within my java program and feed some commands to the program. I use apache commons exec. This is what I have so far:

CommandLine command = new CommandLine("myExec");
DefaultExecuteResultHandler resultHandler = new DefaultExecuteResultHandler();
DefaultExecutor executor = new DefaultExecutor();
ShutdownHookProcessDestroyer processDestroyer = new ShutdownHookProcessDestroyer();
TextareaOutputStream outputstream = new TextareaOutputStream(jTextArea1); //this redirects the output to a text area by extending and overriding outputstream. Works perfect.
PumpStreamHandler streamHandler = new PumpStreamHandler(outputstream, outputstream);
executor.setStreamHandler(streamHandler);
OutputStream out = new ByteArrayOutputStream();
executor.getStreamHandler().setProcessInputStream(out);
executor.setProcessDestroyer(processDestroyer);
executor.execute(command, resultHandler);
out.write("myFile.dat\n".getBytes());

This doesn't work. As soon as my program starts it crashes:

forrtl: severe (24): end-of-file during read, unit 5, file stdin

I also tried with pipedinputstream as here--> Trouble providing multiple input to a Command using Apache Commons Exec and extracting output :

CommandLine command = new CommandLine("myExec");
DefaultExecuteResultHandler resultHandler = new DefaultExecuteResultHandler();
DefaultExecutor executor = new DefaultExecutor();
ShutdownHookProcessDestroyer processDestroyer = new ShutdownHookProcessDestroyer();
TextareaOutputStream outputstream = new TextareaOutputStream(jTextArea1); //this redirects the output to a text area by extending and overriding outputstream. Works perfect.
PipedInputStream stdin = new PipedInputStream();
BufferedOutputStream processInput = new BufferedOutputStream(new PipedOutputStream(stdin));
PumpStreamHandler streamHandler = new PumpStreamHandler(outputstream, outputstream, stdin);
executor.setStreamHandler(streamHandler);
executor.setProcessDestroyer(processDestroyer);
executor.execute(command, resultHandler);
processInput.write("myFile.dat\n".getBytes());
processInput.flush();

With this one, it hangs to the first prompt! As if the flush() has no effect. The terminal program never gets anything.

I also tried with this idea: How to pipe a string argument to an executable launched with Apache Commons Exec?

If I write everything in the ByteArrayInputStream before launching the exec then it WORKS. If I launch the exec and then try to write something then I get again the first error.

Any help would really be appreciated.

Just for completeness (I didn't write this, I don't remember where I got it from the internet). It's for the redirection of the output to a jTextArea:

import java.io.BufferedOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;

class TextareaOutputStream extends OutputStream {

private final JTextArea area;
private final StringBuffer buf = new StringBuffer(128);


public TextareaOutputStream(final JTextArea area) throws IOException {
    this.area = area;
}

@Override
public void write(int c) throws IOException {
    // append character to buffer
    buf.append((char) c);
    // and newline appends to textarea
    if (c == '\n' || c == ':') {
        flush();
    }
}

@Override
public void close() {
    flush();
}

@Override
public void flush() {
    SwingUtilities.invokeLater(new Runnable() {

        String str = buf.toString();

        @Override
        public void run() {
            area.append(str);
        }
    });
    buf.setLength(0);
}

public void message(String msg) {
    if (buf.charAt(buf.length() - 1) != '\n') {
        buf.append('\n');
    }
    buf.append(msg);
    buf.append('\n');
    flush();
}

}