How do I read from BufferedReader real-time from a process output in Java?

Question

I am trying to read real-time the data from a process using a BufferedReader and redirect it to a TextArea. However, I have noticed that when the process is running the .bat, it tends to freeze and cause a lag to the JavaFX TextArea. The ".bat" fiel that runs prints out a ..... one one line to indicate progress, and I believe this is where it is failing at. I had an idea to have the program wait a certain amount of time, then it executes, but because its all on one line it also fails. Please help

Code:

 while(iterator.hasNext()) {
    Map.Entry mentry = (Map.Entry)iterator.next();
    String taskPath = " /k d: && cd DATA\\Virtualization\\Users && ESXRun.bat";
    ProcessBuilder pb = new ProcessBuilder("cmd",taskPath);
    Process process = pb.start();
    BufferedReader stdInput = new BufferedReader(new InputStreamReader(process.getInputStream()));

    String s = "";
    // read the output from the command

    while ((s = stdInput.readLine()) != null) {
        //TextArea
        cliLog.appendText(s);                       
        cliLog.appendText("\n");
    }
    process.waitFor();
    process.destroy();
}

https://stackoverflow.com/questions/13784333/platform-runlater-and-task-in-javafx — SedJ601, Jun 19 '19 at 15:21
JavaFX is single-threaded (and not thread-safe). I/O should not be done on the _JavaFX Application Thread_. Use a background thread and publish any UI updates to the FX thread using `Platform.runLater`. If possible, coalesce updates to avoid flooding the FX thread. — Slaw, Jun 19 '19 at 15:27
@Sedrick Thanks for the reference, however would I be wrapping my entire processbuilder in the task or would it just be the code for the BufferedReader? — tharriott, Jun 19 '19 at 15:35
@tharriott You need to run "while ((s = stdInput.readLine()) != null)" in separate thread and update UI in FX thread using Platform.runLater. Try to start reading simple multi line file to test if your approach works properly. — Oleks, Jun 19 '19 at 15:40
https://stackoverflow.com/questions/36638617/javafx-textarea-update-immediately — Oleks, Jun 19 '19 at 15:50

score 2 · Answer 1 · answered Jun 19 '19 at 18:02

This is just the concept to demonstrate the issue. You have to customize it and handle exceptions.

public class TextAreaBash extends Application implements Runnable {

    private final TextArea textArea = new TextArea();

    public static void main(final String[] args) {
        Application.launch(args);
    }

    @Override
    public void start(final Stage primaryStage) throws Exception {
        primaryStage.setScene(new Scene(new VBox(textArea), 300, 200));
        primaryStage.show();
        ping();
    }

    public void ping() {
        new Thread(this).start();
    }

    @Override
    public void run() {
        try {
            final ProcessBuilder processBuilder = new ProcessBuilder("cmd", "/C", "ping -a www.google.com -n 10");
            final Process process = processBuilder.start();
            final InputStreamReader inputStreamReader = new InputStreamReader(process.getInputStream());
            while (appendText(inputStreamReader)) {
                ;
            }
            process.waitFor();
            process.destroy();
        } catch (final Exception ex) {
            ex.printStackTrace();
        }
    }

    private boolean appendText(final InputStreamReader inputStreamReader) {
        try {
            final char[] buf = new char[256];
            final int read = inputStreamReader.read(buf);
            if (read < 1) {
                return false;
            }
            Platform.runLater(() -> {
                textArea.appendText(new String(buf));
            });
            return true;
        } catch (final IOException e) {
            e.printStackTrace();
        }
        return false;
    }
}

Thanks a million!! I copied the boolean appendText() method and it worked. I believe one of the reasons it was not working for me and would hang is because I was reading it line by line, instead of how you have it by character. Thanks again — tharriott, Jun 20 '19 at 13:19
@tharriott Glad to help. Yeah, looks like readLine method is waiting for line terminators '\n' & '\r' (CRLF) which is actually never happening. — Oleks, Jun 20 '19 at 13:40

How do I read from BufferedReader real-time from a process output in Java?

1 Answers1