DataNucleus "Excel" provides persistence of Java objects to Excel documents. It builds on top of the DataNucleus "core" jar supporting specific features of Excel documents. It provides querying capabilities using JDOQL. The code can be utilised with either JDO or JPA persistence APIs. It makes use of Apache POI.
Support for this persistence layer is provided by way of a Forum at http://www.datanucleus.org.