Even if this functionality changes, I still think that DefaultTreeModel is flawed.
DefaultTreeModel requires the roots to be instantiated for the model to exist (it's part of the constructor). If you source your data from a database and don't store the model in the session or as a singleton this will cause unnecessary hits to the database. For example when expanding a tree node, the model is required but the roots are not. Luckily, TreeModel is an interface and DefaultTreeModel is optional. You can use my LazyTreeModel or similar.
