If the JBoss is down and you use it directly there is no chance because there is no listener process.
As I know a common solution is a apache in front to host the static context and loadbalance the requests.
Here it is possible to switch the static start page to a mantenance page during the JBoss mantenance.
We have Apache server at the front. Where in the server do we need to put this error page and what configuration file do I need to make changes.