DataNucleus supports persistence to heterogeneous datastores and this plugin provides persistence to DB4O.
'org.datanucleus:datanucleus-db4o:2.0.2'
<dependency>
<groupId>org.datanucleus</groupId>
<artifactId>datanucleus-db4o</artifactId>
<version>2.0.2</version>
</dependency>
<dependency org="org.datanucleus" name="datanucleus-db4o" rev="2.0.2"/>
"org.datanucleus", "datanucleus-db4o", "2.0.2"