JDBM provides TreeMap and HashMap backed by disk storage. It is a fast, scalable and easy to use embedded Java database.
'net.kotek:jdbm:4.001-alpha'
<dependency>
<groupId>net.kotek</groupId>
<artifactId>jdbm</artifactId>
<version>4.001-alpha</version>
</dependency>
<dependency org="net.kotek" name="jdbm" rev="4.001-alpha"/>
"net.kotek", "jdbm", "4.001-alpha"