How to create Nested field in index using Java Client 8

Elastic Stack Elasticsearch
1

I have an ES index that is created from Java code level when I index a POJO with ElasticsearchClient.

How do I specify that I need certain fields to be type: "nested" in my index?

2

You have to create the index with an index mapping that defines those fields as nested. With that mapping in place, the corresponding fields will be indexed as nested values.