Bdb-je-playground is a project mainly written in Scala, it's free.
Ryan's BerkeleyDB Java Edition playground
This is a playground for poking at bits of Berkeley DB Java Edition. The playground is built on top of dropwizard exposing several REST endpoints backed by BDB as a data store.
HTTP PUT JSON to /data/{object path} and it will be stored in BDB, keyed by the object path. HTTP GET /data/{object path} to retrieve it. HTTP DELETE /data/{object path} to remove it. Simple, right?
HTTP GET /changes/{timestamp} to get all objects updated on or after the timestamp provided. This is supported internally by a BDB SecondaryDatabase, which is keyed by the modification time of the objects stored in the primary database.