Head over to the following website and grab the most recent “keepalive.zip” file either to your desktop or downloads folder: (do not extract it)
https://github.com/scristalli/sql-developer-keepalive/releases

Open up SQL Developer and go to “Help” → “Check for Updates”

Click on “Install From Local File”, and browse to where you downloaded the keepalive.zip file.

Click “Next”, take all the defaults, then click “Finish”.

Close SQL Developer, then open it again. You should have the following icon on the SQL Developer ribbon:

Click on this button and enter in the number of seconds between which you want the code to ping the database (I usually set it at 600 seconds (10 minutes)). If you click it again, that will toggle it off.