I am going to use redis as the web cache for geoserver, so I need to understand the database connection in geoserver. I have imported geoserver in Eclipse, and there are two projects named gs-sec-jdbc and gs-web-sec-jdbc. I do not know what the “sec" means and what are the differences between these two projects. Any help or tutorial is appreciated！ Thank you !
These two modules are part of the security subsystem (gs-web-sec-jdbc is the web based user interface). They are almost certainly not the modules you are looking for.
If you intend to use Redis to store WMS output images then you need to look at how GeoWebCache works.
If you want to provide a cache between GeoServer and a JDBC database then you will need to explore GeoTools' JDBC datastore mechanism.