Customizable Java-based html editor
 

I'm looking for a customizable html editor, preferably Java-based, that
I can distribute to our customers.

We have an app that allows you to put various UI widgets in a JSP page.
(We may switch to Freemarker, Velocity, or some template language). In
any case, I'd like to give my users the ability to drag a widget from a
palette, fill in a few params, and plunk it on an HTML page. Basic HTML
editing should be enough.

Does anyone know of an existing editor that can be customized in that way?