You should create an entity which is a specialisation if FileDocument. Before the Java action, you should create an object of this entity and associate all the objects on your list with this object.
As the input into the Java action you can then use this new Object (FileDocument). In the export templates you can reach the objects on the list over the association we just set.
Be aware that you will have to commit the FileDocument specialisation in order for this to work.
Hope this helps!