Reading native process standard output stream with ProcessBuilder

Question

Hi,
I'd like to launch an native process (windows application) which writes on standard output during its running.
I'd like to view my application output on a JTextArea on my Java frame (Swing). But I do get all process output
on text area only when the process is finished (it takes about 20 seconds to complete). My external process is
launched by using a ProcessBuilder object.
Here is my code snippet with overridden doInBackground() and process() methods of ProcessBuilder class:
@Override
public String doInBackground() {
jbUpgrade.setEnabled(false);
ProcessBuilder pb = new ProcessBuilder();
paramFileName = jtfParameter.getText();
command = "upgrade";
try {
if (!(paramFileName.equals(""))) {
pb.command(command, jtfRBF.getText(), jtfBaseAddress.getText(), "-param", paramFileName);
} else {
pb.command(command, jtfRBF.getText(), jtfBaseAddress.getText());
pb.directory(new File("."));
pb.redirectErrorStream(false);
p = pb.start();
try {
InputStream is = p.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String line;
jtaOutput.setText("");
while ((line = br.readLine()) != null) {
publish(line);
} catch (IOException ex) {
Logger.getLogger(CVUpgradeFrame.class.getName()).log(Level.SEVERE, null, ex);
} catch (IOException ex) {
Logger.getLogger(CVUpgradeFrame.class.getName()).log(Level.SEVERE, null, ex);
jtaOutput.setText("");
jtaOutput.setLineWrap(true);
jtaOutput.append("Cannot execute requested commmad:\n" + pb.command());
jtaOutput.append("\n");
jtaOutput.setLineWrap(false);
return "done";
@Override
protected void process(List<String> line) {
jtaOutput.setLineWrap(true);
Iterator<String> it = line.iterator();
while (it.hasNext()) {
jtaOutput.append(it.next() + newline);
jtaOutput.repaint();
//Make sure the new text is visible, even if there
//was a selection in the text area.
jtaOutput.setCaretPosition(jtaOutput.getDocument().getLength());
How can I get my process output stream updated while it is running and not only when finished?
Thanks,
jluke

Answer 1

1) Read the 4 sections of http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html and implement the recommendations. Although it is concerned with Runtime.exec() the recommendations still apply to Process generated by ProcessBuilder.
2) Read about concurrency in Swing - http://java.sun.com/docs/books/tutorial/uiswing/concurrency/ .
3) Use SwingUtilities.invokeLater() to update your GUI.