Hello,
In KML, a folder is a container for placemarks (marker, polygons...). You can't add an icon to a placemarks container, that's why it isn't possible with JAK I guess. You can see the reference for all KML elements here :
https://developers.google.com/kml/documentation/kmlreference#folder .
But you can add an icon to a point for example :
With JAK :
Kml kml = new Kml();
Folder folder = kml.createAndSetFolder();
Style myStyle = folder.createAndAddStyle().withId(myStyleID);
myStyle
.withIconStyle(
new IconStyle()
.withIcon(
new Icon()
.withHref(
iconURL))
.withScale(1));
folder.createAndAddPlacemark().withStyleUrl(#myStyleID).createAndSetPoint().withCoordinates(
someCoordinates);
Something like that should work. :)