sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
The most likely cause of this error would be a mis-configured keystore. Can you show us the Connector definition in server.xml for port 8443?
You say that there are
2 applications deployed in the server, but "the" application is accessible via SSL. Have you tested both of them? What do your URLs look like?
Finally, what does the logic that app1 uses to access app2 look like?
The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.
You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.