The user goes to the APEX URL via the browser, it's forwarded by the weblogic plug-in to the APEX Listener, which in turn forwards it to the DB. The APEX application processes the request and does its thing to generate an HTML page and returns it eventually to the browser. On and on, etc.
My question is this. Does the APEX listener in this type of scenario send any application specific sql or pl/sql calls to the Database (other than dealing with the connection pool) for processing by the application or does it just act as a proxy and forward HTML to the database for processing by the DB/APEX application which does all the pl/sql calls?
My colleague wants to turn on caching on the APEX Listener but I'm thinking this won't help because I assumed that the listener doesn't generate any application specific SQL or PL/SQL calls to be cached.
Yes, file content and that too fetched through db procedures.
You have a choice of deployment when to comes to static files like images, css,etc. You could deploy them on OHS or WLS and their caching will be handled by OHS or WLS , respectively.
For SQL and DB calls there is the Connection Pool.