This fictional application we're working on is a typical Order Service
that can allow online, physical stores, or even
partners to place orders for our fresh-backed pastries! For that, the Order Service
is exposing a REST API to its consumers
but also relies on an existing API we have introduced in a previous post 😉
The Order Service
application has been designed around 5 main components that are directly mapped on Spring Boot components and classes:
- The
OrderController
(in packagecontroller
) is responsible for exposing anOrder API
to the outer world. - The
OrderService
is responsible for implementing the business logic around the creation of orders. - The
PastryAPIClient
is responsible for calling thePastry API
in Product Domain and get details or list of pastries. - The
OrderEventPublisher
is responsible for publishing a message on aKafka
topic when a newOrder
is created. - The
OrderEventListener
is responsible for consuming message on aKafka
topic when anOrder
has been reviewed.
Of course, this is a very naive vision of a real-life system as such an application would certainly pull out much more
dependencies (like a Payment Service
, a Customer Service
, a Shipping Service
, and much more) and offer more complex API.
However, this situation is complex enough to highlight the two problems we're addressing:
- How to efficiently set up a development environment that depends on third-party API like the Pastry API?
- You certainly want to avoid cloning this component repository and trying to figure out how to launch and configure it accordingly.
- As a developer, developing your own mock of this service makes you also lose time and risk drifting from initial intent,
- How to efficiently validate the conformance of the
Order API
andOrder Events
against business expectations and API contracts?- Besides the core business logic, you might want to validate the network and protocol serialization layers as well as the respect of semantics.
This application must implement basic flows:
- When creating a new
Order
, the service must check that the products are available before creating and persisting an order. Otherwise, order cannot be placed. - When the
Order
is actually created, the service must also publish anOrderEvent
to a specific Kafka topic to propagate this information to other systems that will review the events, - When the
OrderEvent
has been reviewed, a new message is published on anotherKafka
topic. TheOrderEventListener
must capture-it and update the correspondingOrder
status using the service.
All the interactions are specified using API contracts:
- The Order API is specified using the
order-service-openapi.yaml
OpenAPI specification, - The Pastry API is specified using the
apipastries-openapi.yaml
OpenAPI specification, - The Order Events are specified using the
order-events-asyncapi.yaml
AsyncAPI specification.
Those specifications will help us for two things:
- They will be used to provide simulations (or mocks) of third-parties systems - typically the Pastry API provider and the reviewer system that provides updates on
OrderEvents
- They will be used to allow checking the conformance of the provided
Order API
and the publishedOrder Event
on order creation.