https://medium.com/hotels-com-technology/how-expedia-is-getting-rid-of-java-bean-transformers-6ea5ce3a511f

In a layered architecture, where you are creating levels of abstraction by encapsulating changes to particular data objects and propagating these to other layers, the object mapping process can become mandatory and cumbersome.

The data object mapping has traditionally been addressed by hand coding transformers that copy data between the entities (or Java Beans).