MapDB documentation is hosted on Git Books. There are PDF and ebook versions available for download.
Code examples from documentation are available in Github repository.
Here is Javadoc for latest version.
MapDB is written in Kotlin. It has very good compatibility with Java, but uses different documentation tool. Here is Dokka for latest version.
TODO archive links to older versions of Javadoc and Dokka.
1.0 and 2.0 documentation
1.0 and 2.0 branches are no longer supported. Here is archived PDF documentation and older version examples.