Java api client example for rollover

Is there a centralized place with examples of how java API clients are being invoked?
It seems to be very lacking even after several years deprecating the old REST client.

I am trying to figure out how to issue rollover API in JAVA. Any pointers?

I don't have yet this one specifically but some resources here:

Do you have an example of bulkIndex with script?

Also how to check if a document exists?
I can find code that does check if an index exists, but not for a document via _id.

version 8.10.2

Never mind. found the solutions.

exist = ES.exists(e -> e
.index(index)
.id(docId)).value();