Looks ok - although I have to say that EntitySource has become so complex now that it's hard to understand (for example: enrichFunction returns a function take takes a Pair, which should contain the entity data as key and the entity or entities to enhance with as value. This pair is generated in enrich etc.). I don't see an easy way to improve this, besides enhancing javadoc (the description "Method to build an enrich function." is used everywhere, although the functions do very different things, for example).