How to Safely Update JavaFX UI from Background Database Threads?

Using Threads to Make Database Requests with JavaFX

JavaFX dictates two fundamental rules regarding threads:

1. Any interaction with a scene graph node's state should be executed on the JavaFX application thread.
2. Lengthy operations should be executed on a background thread.

Exception Encountered

The exception you encountered originates from attempting to update the UI (courseCodeLbl.setText(...)) from a thread other than the JavaFX application thread.

Implementing Threading Correctly

To ensure database requests are executed in a separate thread, follow these steps:

• Create a Runnable class and implement the run() method that contains the database request.
• Pass an instance of this class to the Thread constructor and start the thread.
• Use Platform.runLater(Runnable r) to update the UI with the database results.

Implementing Threading Using JavaFX.concurrent

JavaFX provides the Task class specifically designed for managing background threads and updating the UI.

• Create a Task object and define the database call in the call() method.
• Use updateProgress(...) and updateMessage(...) to update the UI during execution.
• Register setOnSucceeded(...) and setOnFailed(...) handlers to process results and handle errors.
• Invoke the task using a Task.Executor (e.g., Executors.newCachedThreadPool).

Sample Implementation

Task<Course> courseTask = new Task<Course>() {
    @Override
    public Course call() throws Exception {
        return myDAO.getCourseByCode(courseCode);
    }
};
courseTask.setOnSucceeded(e -> {
    Course course = courseTask.getCourse();
    if (course != null) {
        courseCodeLbl.setText(course.getName());
    }
});
exec.execute(courseTask);

In this example, the database access is performed in a task, and the UI update is scheduled on the JavaFX application thread using the setOnSucceeded handler. By following these guidelines, you can effectively use threads to optimize database requests while maintaining UI responsiveness in JavaFX applications.

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