Access index mapping in FieldMapper#parseCreateField

I'm really new in Elasticsearch.
I'm creating a custom mapper extending from FieldMapper, using Java Api, and I need to access to the current index mapping configuration when new data will inserted. I search in ParseContext but I can't find any solution. Then I try throught NodeBuilder#nodeBulder#client but this solution is to slow.
So my question is:
How I can efficiently access to index mapping configuration in FieldMapper#parseCreateField?