Code

diagramView.addMouseWheelListener(new MouseWheelListener() {

	public void mouseWheelMoved(MouseWheelEvent e)
	{
		Point2D scrollPos = new Point2D.Float(
			diagramView.getScrollX(),
			diagramView.getScrollY());
		Point scrollPosDev = diagramView.docToDevice(scrollPos);
		Point mousePosDev = e.getPoint();
		Point2D mouseDocPos = diagramView.deviceToDoc(mousePosDev);

		Point mouseOffset = new Point(
			mousePosDev.x - scrollPosDev.x,
			mousePosDev.y - scrollPosDev.y);

		float oldZoom = diagramView.getZoomFactor();
		float newZoom = oldZoom + (float)e.getWheelRotation() / 2;
		diagramView.setZoomFactor(newZoom);

		Point2D mouseOffsetDoc = diagramView.deviceToDoc(mouseOffset);
		float sx = (float)(mouseDocPos.getX() - mouseOffsetDoc.getX());
		float sy = (float)(mouseDocPos.getY() - mouseOffsetDoc.getY());
		diagramView.scrollTo(sx, sy);
	}});