Previously the setSource methods and other methods that accepted byte/string representations of an object source did not require the XContentType to be specified. The auto-detection of the content type is no longer used, so these methods now require the XContentType as an additional argument when providing the source in bytes or as a string.

In previous versions of Elasticsearch, delete by query requests without an explicit query were accepted, match_all was used as the default query and all documents were deleted as a result. From version 6.0.0, a DeleteByQueryRequest requires an explicit query be set.

The count value in the stats aggregation represents a doc count that shouldn’t require a formatted version. This method was deprecated in 5.4 in favour of just using String.valueOf(getCount()) if needed

When sending a request through the request builders e.g. client.prepareSearch().execute(), it used to be possible to call addListener against the returned ListenableActionFuture. With this change an ActionFuture is returned instead, which is consistent with what the Client methods return, hence it is not possible to associate the future with listeners. The execute method that accept a listener as an argument can be used instead.

The terms, histogram, and date_histogram aggregation code has been refactored to use common code for ordering buckets. The BucketOrder class must be used instead of Terms.Order and Histogram.Order. The static methods in the BucketOrder class must be called instead of directly accessing internal order instances, e.g. BucketOrder.count(boolean) and BucketOrder.aggregation(String, boolean). Use BucketOrder.key(boolean) to order the terms aggregation buckets by _term.

In BulkResponse, SearchResponse and TermVectorsResponse getTookInMiilis() method has been removed in favor of getTook method. getTookInMiilis() is easily replaced by getTook().getMillis().

As GetField and SearchHitField have the same members, they have been unified into DocumentField.

The classes for the variants of the range aggregation (geo_distance, date and ip) were moved into the org.elasticsearch.search.aggregations.bucket.range package.

The org.elasticsearch.search.aggregations.bucket.terms.support package was removed and the classes were moved to org.elasticsearch.search.aggregations.bucket.terms.

The filter aggregation classes were moved to org.elasticsearch.search.aggregations.bucket.filter

It is now required to include the desired ranks as a non-null, non-empty array of doubles to the builder’s constructor, rather than configuring them via a setter on the builder. The setter method values() has correspondingly been removed.