Len Bass, Paul Clements, and Rick Kazman best explain the Layered Architecture as, “The Layered Architecture Pattern defines layers as a grouping of modules or services and a unidirectional allowed-to-use relation among layers. Layers must have a strict-ordering relation, in which a layer can only use public interfaces of a layer below,” in the book Software Architecture in Practice1.
The benefit of the layered-architecture is that it allows for a separation of concerns, allows for a division of labor, and it is typically easy to refactor a top layer.
Its drawback is that there is a performance cost for each layer, and it can be very expensive to refactor lower layers.
The Layered Architecture applied as reference architecture for a RESTful Application
The Presentation Tier
A well-designed architecture could easily switch Presentation Layer implementations with different technologies. Perhaps this could be a Swing Application, Command Line Application, or MVC framework with server side templating. This particular example documents a Layered REST application.
Serialization Segment
The Serialization segment provides a set of classes per each serializable request and response types (i.e. Plain Ordinary Java Object that Jackson could easily convert to and from JSON).
Transformer Segment
The Transformer segment will convert serializable request and response classes into Domain / Model classes.
REST Endpoint Declarations Segment
The REST Endpoint Declarations will each declare a PATH, an Accept type, a Content-Type, a serializable request class, and a serializable response class.
It will receive the Serializable Request, transform it into the appropriate Domain / Model class, and call the appropriate Business Logic Service class, transform the result into Serializable Response, and finally respond.
Business Logic Services Layer
The Business Logic Services Layer receives a domain object from the Presentation Layer, and provides business functionality. It will use the Client Interface to communicate to other components in a system or the Persistence Layer to persist data.
Client Interface Layer or Persistence Layer
The Client Interface Layer is responsible for sending or receiving data from other systems. This might also be a Persistence Layer that merely persist data into a data-store. For example, this could be a set of Data-access Objects that use JPA.
Domain / Model Layer
The Domain / Model layer should attempt to provide an object-oriented model of your business. It is good to implement business logic here, but keep in mind that business logic computations often require external persistence, and it is anti-pattern to couple persistence technologies with a domain object. These absolutely should be Plain Ordinary Java objects, and depending your threading model, perhaps immutable as well.