In some cases, applications may want to use Glassfish-specific API to test
whether a given username is valid (i.e. just the fact that the user exists,
without testing any credentials).
There is already a method in com.sun.enterprise.security.auth.realm.Realm called
getUser( String name ) that is supposed to do this, however the
com.sun.appserv.security.AppservRealm base class provides a default
"unsupported" implementation of this class.
The JDBCRealm class does not implement this method, so this method remains
unsupported. I did notice that the FileRealm implements this method.
It would be good for the JDBCRealm to support this as well. It should be able
to do it since it has access to the username column in the database.