scroll pane can't align it's content

When a Node(group fro example) is added into a scroll pane, the scroll pane automatically align the node to the upper left corner of the scroll pane's content area. How can i customize the Node's alignment(the middle center eg) in the scroll pane. When the Node's size is scaled and larger than the scroll pane's size the scroll pane's scroll bar appears, and if the Node's size shrinks and it's size becomes smaller than the scroll pane's then the Node is aligned to the middle center. it seems don't take affect if i override the scroll pane's layoutChildren method and set layoutX and layoutY property of the Node.