This project is a sample implementation of the Restbucks application described in the book REST in Practice by Jim Webber, Savas Parastatidis and Ian Robinson. It's a showcase for bringing different Spring eco-system technologies together to implement a REST web service.
The project uses:
- Spring (MVC) - 3.2.0.M2
- Spring Data JPA - 1.2.0.RELEASE
- Spring Data REST - 1.0.0.RELEASE
- Spring Hateoas - 0.4.0.BUILD-SNAPSHOT
- Spring Plugin - 0.8.0.BUILD-SNAPSHOT
The implementation consists of mainly two parts, the order
and the payment
part. The Orders
are exposed as REST resources using Spring Data RESTs capability to automatically expose Spring Data JPA repositories contained in the application. The Payment
process and the REST application protocol described in the book are implemented manually using a Spring MVC controller (PaymentController
).
Here's what the individual projects used contribute to the sample in from a high-level point of view:
The Spring Data repository mechanism is used to reduce the effort to implement persistence for the domain objects to the declaration of an interface per aggregate root. See OrderRepository
and PaymentRepository
for example. Beyond that, using the repository abstract enables the Spring Data REST module to do its work.
We're using Spring Data REST to expose the OrderRepository
as REST resource without additional effort.
Spring Hateoas provides a generic Resource
abstraction that we leverage to create hypermedia-driven representations. Spring Data REST also leverages this abstraction so that we can deploy ResourceProcessor
implementations (e.g. PaymentorderResourceProcessor
) to enrich the representations for Order
instance with links to the PaymentController
. Read more on that below in the Hypermedia section.
The final important piece is the EntityLinks
abstraction that allows to create Link
instance in a type-safe manner avoiding the repetition of URI templates and parts all over the place. See PaymentLinks
for example usage.
The Spring Plugin library provides means to collect Spring beans by type and exposing them for selection based on a selection criterion. It basically forms the foundation for the EntityLinks
mechanism provided in Spring Hateoas and our custom extension RestResourceEntityLinks
.
The project uses Lombok to reduce the amount of boilerplate code to be written for Java entities and value objects.
A core focus of this sample app is to demonstrate how easy resources can be modeled in a hypermedia driven way. There are two major aspects to this challenge in Java web-frameworks:
-
Creating links and especially the target URL in a clean and concise way, trying to avoid the usage of Strings to define URI mappings and targets and especially the repetition of those. On the server side, we'd essentially like to express "link to the resource that manages
Order
instances" or "link to the resource that manages a singleOrder
instance. -
Cleanly separate resource functionality implementation but still allowing to leverage hypermedia to advertise new functionality for resources as the service implementation evolves. This essentially boils down to an enrichment of resource representations with links.
In our sample the core spot these challenges occur is the payment
subsystem and the PaymentController
in particular.