How to intercept/capture MouseWheelEvent from JScrollPane

Question

Suppose you want to have your own MouseWheelListener handle MouseWheelEvents that take place within a JScrollPane under some circumstances. Say, repurposing alt+wheel for zooming in/out, while leaving the wheel's normal behavior (scrolling content within the JScrollPane) when the alt key ISN'T simultaneously depressed during scroll activity.
What do you need to do to make it work?
Is it necessary to put a key listener on the JScrollPane that calls setWheelScrollingEnabled(false) whenever the alt key gets pressed, and calls setWheelScrollingEnabled(true) whenever the alt key gets released (and possibly registers and deregisters the JScrollPane as a MouseWheelListener as well)? Or is there some alternate strategy that would let me put my MouseWheelListener ahead of the JScrollPane in the event bubbling hierarchy so my MouseWheelListener would get a chance to handle the event first and zoom if isAltDown() == true, or cooperatively pass it along to the next MouseWheelListener in line instead of consuming the event if it's false?

Answer 1

Ideas:
1) Disable the wheel for the scrollpane (setWheelScrollingEnabled(false), as you suggested), capture the mouse wheel event as a separate event and process the scrolling manually (using addMouseWheelListener and calling either getVerticalScrollBar().setValue() to scroll, and some other method to zoom).
To capture the event, you could use
    Toolkit.getDefaultToolkit().addAWTEventListener(
        someListener, AWTEvent.MOUSE_WHEEL_EVENT_MASK  );or
    Component.addMouseWheelListener( someListener );2) Overload processMouseWheelEvent at some level (perhaps in your own extension of JScrollPane, though you may have to do it somehwere deeper) and pick out the alt combinations before calling super.ScrollPane.processMouseWheelEvent