Sometimes there is a need to change the default Divider LaF appearance.
JSplitPane lacks of a method to get the Divider component. There is only a tricky way to get it through BasicSplitPaneUI:

SplitPaneUI splitUI = splitPane.getUI();
if (splitUI instanceof BasicSplitPaneUI) {
    BasicSplitPaneDivider div = ((BasicSplitPaneUI) splitUI).getDivider();
}

Obviously this will not work if the UI doesn't extend BasicSplitPaneUI.

I see three steps on the way to solve the problem:
1. Add to JSplitPane a method, which will return the Divider component. Something like this:

public JDivider getDivider(){}

2. Create a JDivider class, which will be the parent of all dividers.

3. Make the JDivider the parent of BsicSplitPaneDivider.