How Can I Use JavaFX Threads to Efficiently Handle Database Requests?

Using threads to make database requests

JavaFX provides a concurrency API specifically designed for executing code in a background thread, with API specifically designed for updating the JavaFX UI on completion of (or during) the execution of that code. The key class in javafx.concurrent is Task, which represents a single, one-off, unit of work intended to be performed on a background thread. This class defines a single abstract method, call(), which takes no parameters, returns a result, and may throw checked exceptions. To correctly implement threading for database requests, the long-running operation (database access) should be performed in a background thread, returning the results of the operation when it is complete, and then schedule an update to the UI on the UI (FX Application) thread using Platform.runLater(Runnable r) to execute r.run() on the FX Application Thread.

General Good Practices for Multithreading

• Structure code that is to be executed on a "user-defined" thread as an object that is initialized with some fixed state, has a method to perform the operation, and on completion returns an object representing the result.
• When mutable state needs to be shared between multiple threads, carefully synchronize access to that state to avoid observing the state in an inconsistent state.

Using the javafx.concurrent API

1. Create a Task to handle the call to the database.
2. Initialize the Task with any state that is needed to perform the database call.
3. Implement the task's call() method to perform the database call, returning the results of the call.
4. Register a handler with the task to send the results to the UI when it is complete.
5. Invoke the task on a background thread.

For example:

final int courseCode = Integer.valueOf(courseId.getText());
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);

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