Java persistence using JDO, JPA or REST
An object relational-mapping (ORM) library for Java
Java Application Framework
eXist-db is a feature rich Open Source native XML database
CrNiCKL (chronicle) is a Java database for time series
Distributed, transactional key-value store
Big Sack: A lightweight Java Key/Value store with undo and disk cache.
Simple persistent framework
ChronoDB is a data manager for generic time series.