How to parse a nested unpredictable parameterised Json without creating any POJO?

Receiving JSON input from server whose parameter name may change with time. output format which also will be a json is fixed. But input json may change as it comes from different publishers. Client want an externaal mapping file(json format also) which they will only modify if input json property name needs to be modified or extra parameter is needed. It's spring boot project. Input Json will be nested and may not be nested depending on the publishers.