A、Sessions can't be preserved when redeploying applications. The customer needs to consider redeployment during late nights when the traffic is low.  

B、Change the flag responsible for the development mode of their environment. In the production mode, all sessions are preserved while redeploying application.  

C、Change Hotspot to JRockit. Sessions can't be preserved on HotSpot when redeploying application. 

D、Use flag -version when redeploying the application. This will switch on the Side By Side deployment feature and preserve existing sessions.

E、Open a service request with Oracle Support. This is unexpected behavior. Sessions are  preserved without any extra settings.