I think Olivier simply wants to get an event when the user scrolls horizontally. For vertical scrolling there is MouseWheelListener with MouseWheelEvent, but there is no such thing for horizontal scrolling yet. There's already an accepted but unsolved bug report for that.
If the component itself supports horizontal scrolling then you can use an AdjustmentListener on the JScrollPane's horizontal scroll bar. This will be notified when the scroll bar's position changes, a side effect of the scrolling.