I am working on a RSS reader application. And I need to find a backend database. I want the database be embedded because I don\'t want the users to install a database server
How about Couchbase Lite? It's an open source, embeddable document database. While it can function as a standalone document database, its real value is in its ability to synchronize with remote document databases. It may be aimed at iOS / Android, but it can run on anything with a JVM.
https://github.com/couchbase/couchbase-lite-java