GetUserDetailsUsecase.java

public class GetUserDetailsUsecase {

    private final DB db;

    @Inject public GetUserDetailsUsecase(DB db) {
        this.db = db;
    }

    public Observable<UserDetails> getUserDetails() {
        return Observable.create(new Observable.OnSubscribe<UserDetails>() {
            @Override public void call(Subscriber<? super UserDetails> subscriber) {
                try {
                  UserDetails userDetails = ... //retrieve data from database here
                    if (!subscriber.isUnsubscribed()) {
                        subscriber.onNext(userDetails);
                        subscriber.onCompleted();
                    }
                } catch (Exception ex) {
                    Log.e(ex, "error while retrieving user details");
                    if (!subscriber.isUnsubscribed()) {
                      subscriber.onError(ex);
                    }
                }
            }
        });
    }
}