After migrating existing Oracle MAF applications to MAF 2.3, your source code shows the following deprecation warning
This deprecation is not mentioned in the Release Notes for MAF 2.3 but in the Oracle MAF Developer Guide, which you may not re-read for each new release: thus this blog article.
The deprecation warning above however does not mean that the RestServiceAdapter class is going away. Instead it is replaced with the RestServiceAdapter class. Confused? Well, as you probably guessed from the previous sentence, the change is in the package location of the class, which changes from oracle.adfmf.dc.ws.rest to oracle.maf.api.dc.ws.rest.
But refactoring the "adfmf" string to the "maf" product identifier is not the only change that comes with this. The call you do to obtain an instance of RestServiceAdapter does change too.
Instead of calling Model.createRestServiceAdapter(), which you did prior to MAF 2.3, you now use the RestServiceAdapterFactory
RestServiceAdapter restServiceAdapter = RestServiceAdapterFactory.newFactory().createRestServiceAdapter();
Working with the RestServiceAdapter itself doesn't change much except for a few method having new names like setRequestMethod and getRequestMethod that replace setRequestType and getRequestType (which I think is a sensible change).
So what now? Actually there is no need to do anything in the short term. However in the mid term we suggest to change the use of RestServiceAdapter to the new class so you are on the latest version of the supported API.