For users of the opensearch-java client.
We have contributed a port of Bulk Ingest Helper, which is similar to the RestHighLevelClient’s BulkProcessor.
This means your client code can simply add documents to the bulk helper, and the helper will take care of constructing bulk requests, thread pools, throttling etc, while sending callbacks to your application of bulk statuses.
The contribution was accepted just after the v3.4 release, so hopefully it will appear in next v3.x version.