First JavaFX application with long sequential processes

Question

Hi all,
I'm working on my first JavaFX application.  I have UI elements (view) in place, I have a controller that works properly (with the exception I'll mention below), and I have an model that runs correctly (processes the data properly), but the model code was not originally written to run under a UI.
What I want to happen is the following.  When the "Run" button is clicked, the input of the user is passed to the model via the controller and the data is processed.  It's a do-once kind of thing where the input is transformed into the output and that's the end of it.  The UI can be reset and new input provided, and the whole thing happens again with the click of the Run button.  Here's the problem:  The processing has several steps that need to happen sequentially, but some can take a long time.  I want to provide feedback via a message (what's being done), and overall progress via a progress bar (both elements in the current UI).  The problem is I'm still very confused about how to accomplish the user feedback.
The UI was built in SceneBuilder, and I've assigned the onMouseClicked event to call the runButtonClicked() method in the controller.
The runButtonClicked() method calls private methods that execute the processing steps (I'm going to do something more intelligent with the exceptions - please ignore that for the time being)...
    public void runButtonClicked() {
        runButton.setDisable(true);
        sdfFileBrowseButton.setDisable(true);
        outputFileBrowseButton.setDisable(true);
        try {
            prepareSDFFile();
            prepareModels();
            collectDescriptors();
            makeSamples();
            evaluateSamples();
            writeResultsToTextFile(results, outputFile);
        } catch (IOException exception) {
            System.out.println("Caught IOException: " + exception.getMessage());
        } catch (JAXBException exception) {
            System.out.println("Caught JAXBException: " + exception.getMessage());
Each of the calls in the try-catch are tasks that need to occur sequentially in the order shown.  A few can take a long time (e.g. collectDescriptors(), evaluateSamples(), and writeResultsToTextFile().  The actual work isn't done in the controller.  The controller creates instances of the classes that do the actual work (this seems to be a departure from most of the tutorials I've seen - it seems the model and the controller are mixed in the tutorials).
I want to alert the user about what step is executing (by way of a message in the UI) and what stage the whole process is in (by way of a progress bar).  It would be nice if the progress bar could reflect the progress of each individual step (returning to 0 at the beginning of the next step), but having the bar just reflect the over all progress (e.g., how many of the six steps have been finished) would be sufficient.
I also want to be able to handle a Cancel button event and just stop the whole process and reset the application (losing whatever work has been done is OK).
So - I really can't tell what the best approach should be.  None of the examples in several tutorials I've gone over have really touched on this type of sequential process.  I'd appreciate suggestions.
Thanks,
Dave.

Answer 1

Suggested Approach
What you describe is an absolutely classic case for using the javafx.concurrent utilities (Task and Service).
Your application is a perfect fit for using these services, which will provide you:
1. a concurrent execution thread to run your log running processes
2. a threadsafe feedback mechanism for progress that you can bind to a ProgressBar for interactive progress feedback.
3. a threadsafe feedback mechanism for messages that you can bind to a Label for interactive status feedback.
4. sample code that demonstrates the ability to cancel and restart processes.
5, a success callback method setter that can be set to provide a result and take action on success.
6. a failure callback method setter that can be set to provide an exception and take action on failure.
Task and Service Samples
There are many examples of Task usage if you search for JavaFX Task.
There is also great documentation in the Task and Service javadoc.
Here is an example of using a JavaFX service.  The example is a little old and uses doesn't use some new API features such as setOnSucceeded or setOnFailed, it also uses the now-deprecated Builder patterns, however, the bulk of it should still be relevant to what you want.
Here is another more complicated sample to Render 300 charts off screen and save them to files in JavaFX, though I doubt your task needs to be that complicated, and likely a single controlling service is all you need, so don't pay too much attention to the more complicated example unless you must have that kind of functionality.
Here is another simpler example for Re: Creating multiple parallel tasks by a single service, that actually demonstrates sequential and parallel demonstration of step tasks within a service.
The progress can be reset between steps, so that the message indicates the step being performed and the progress indicates the progress of the step rather than overall progress.  You could expose separate mechanisms for feeding back overall progress in addition to step progress.
For further help
If you are still having issues, I'm sure somebody on the forum could easily mock up a sample application stub that demonstrates the techniques based on the info you provided in your question, just ask if you would like that...