The time has finally to come to start the work on an (for the moment) internal Filter API and Query Language.
The idea is to have a filter API which can be fed with a filter model so that searches can be performed by the backend in the technology suited base for the backend. So the approach may be: read filter string from configuration -> parse to generic model instance -> provide to search. And now the search can for example use Java 8 streams to perform the search or transform the filter model to a JPA criteria query and let the database to the job.
Thanks for your help!