How can I display a GeoServer's Map inside a Java's Desktop Application?
I would like to display it inside a Java App instead of a browser. Is this possible?
Short answer: yes, you can display a WMS generated map in a desktop app.
Longer answer: It depends, at it's simplest a WMS map (what GeoServer sends you) is just an image generated by a get request to a well known URL scheme. So any app which can request URLs can display WMS maps (so in principal any Java app should be able to do it). However the WMS specification is quite long and complicated and the resulting URLs are quite long and complicated, and as your viewer moves around the map or zooms in and out the URL changes in subtle ways. There are various exciting failure modes in WMS which you will need to watch out for.