How to Properly Implement Threading for Database Requests in JavaFX to Avoid UI Blocking?

Implementing Threading for Database Requests

You encounter an exception due to accessing the JavaFX UI from a separate thread. Here's how you can correctly implement threading:

General Principles of Threading in JavaFX

• Rule 1: Any modification or access to the scene graph must be performed on the FX Application Thread.
• Rule 2: Long-running operations should be executed on non-FX Application Threads.

Implementation Using Threads

Create a thread and start the database request on it:

Thread t = new Thread(new Runnable() {
    public void run() {
        requestCourseName();
    }
}, "Thread A");

t.start();

Using JavaFX Concurrent API

The javafx.concurrent API provides a convenient way to manage background threads and update the UI.

• Task: Encapsulate the background operation.
• Background Task Thread: Executes the Task's call() method on a background thread.
• FX Application Thread: Updates the UI on completion via event handlers registered to Task.

Example Using WidgetDAO and Task

// DAO encapsulates database access
public class WidgetDAO {
    public List<Widget> getWidgetsByType(String type) { ... }
}

// Controller handles UI operations
public class MyController {
    private WidgetDAO widgetAccessor;
    private Executor exec;

    public void searchWidgets() {
        String searchString = widgetTypeSearchField.getText();
        Task<List<Widget>> widgetSearchTask = new Task<>() {
            @Override
            protected List<Widget> call() throws Exception {
                return widgetAccessor.getWidgetsByType(searchString);
            }
        };

        widgetSearchTask.setOnSucceeded(e -> widgetTable.getItems().setAll(widgetSearchTask.getValue()));
        exec.execute(widgetSearchTask);
    }
}

Example Using MyDAO and Task

// DAO encapsulates database access
public class MyDAO {
    public Course getCourseByCode(int code) { ... }
}

// Controller handles UI operations
public class MyController {
    private MyDAO myDAO;
    private Executor exec;

    public void searchCourse() {
        int courseCode = Integer.valueOf(courseId.getText());
        Task<Course> courseTask = new Task<>() {
            @Override
            protected Course call() throws Exception {
                return myDAO.getCourseByCode(courseCode);
            }
        };

        courseTask.setOnSucceeded(e -> {
            Course course = courseTask.getValue();
            courseCodeLbl.setText(course.getName());
        });
        exec.execute(courseTask);
    }
}

By implementing threading correctly, you ensure that long-running database requests do not block the UI thread, resulting in a responsive user interface.

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