public class MyWidget extends EditorPart {

private Composite drawingArea;

public void createPartControl(Composite parent) {
    // Maybe I should use style SWT.NO_BACKGROUND here? Or SWT.EMBEDDED?
    this.drawingArea = new Composite(parent, SWT.NONE);
    // Send value of this.drawingArea.handle to C++ for creation of the C++ widget

    this.drawingArea.addKeyListener(new KeyListener() {
            @Override
            public void keyPressed(KeyEvent e) {
                System.err.println("key pressed " + e.toString());
                // Send key event top C++
            }

            @Override
            public void keyReleased(KeyEvent e) {
                System.err.println("key released " + e.toString());
                // Send key event to C++
            }
        });
}

private void called_from_c_plus_plus() {
    // this code is called through JNI by C++
    // when a click in the C++ widget is detected
    if ( this.drawingArea != null)
        this.drawingArea.setFocus();
}