DataNucleus supports persisting/retrieving objects to/from Excel documents (using the datanucleus-excel plugin, which makes use of the Apache POI project). Simply specify your "connectionURL" as follows
datanucleus.ConnectionURL=excel:file:myfile.xls
replacing "myfile.xls" with your filename, which can be absolute or relative. This connects to a file on your local machine. You then create your PMF/EMF as normal and use JDO/JPA as normal.
The jars required to use DataNucleus Excel persistence are datanucleus-core, datanucleus-api-jdo/datanucleus-api-jpa, datanucleus-excel and apache-poi
There are tutorials available for use of DataNucleus with Excel for JDO and for JPA
Things to bear in mind with Excel usage :-