You are looking at documentation for an older release. Not what you want? See the current release documentation.
The update API also support passing a partial document, which will be merged into the existing document (simple recursive merge, inner merging of objects, replacing core "keys/values" and arrays). For example:
UpdateRequest updateRequest = new UpdateRequest("index", "type", "1") .doc(jsonBuilder() .startObject() .field("gender", "male") .endObject()); client.update(updateRequest).get();