If you use a Reactor with the watchlist disabled, the application needs to resubscribe for items when the connection and service are up. You can refer to the com.refinitiv.eta.valueadd.examples.consumer example in the RTSDK Java package.
Otherwise, you can use a Reactor with the watchlist enabled.
The watchlist automatically recovers data streams in response to failure conditions, such as disconnects and unavailable services, so that applications do not need special handling for these conditions. As conditions are resolved, the watchlist will re-request items on the application’s behalf. Applications can also use this method to request data before a connection is fully established
You can refer to the com.refinitiv.eta.valueadd.examples.watchlistconsumer example in the RTSDK Java package.