This project provides Java API for both client (GWT, with "g-" prefix) and server (Vaadin) side for the popular Leaflet add-on.
Realeases can be downloaded form https://vaadin.com/directory
Vaadin API for Leaflet: V-Leaflet
During development you might need to have development version of v-leaflet, g-leaflet and possibly g-leaflet-draw as well.