Out of the box, GeoServer does not support Oracle databases as a data source. However, there is an extension available that enables support for it as a data source. We just need to add the extension into our GeoServer instance and configure a connection to our database.
To add support for Oracle databases, we need to download the extension. We must ensure we choose the download matching the version of GeoServer that we installed. We have been using the stable version (which at the time of writing is 2.5.2), so this is the version of the extension that we need to download. In your favorite browser, go to http://geoserver.org/release/stable and choose the Oracle option under the Extensions