I'm still quite new to microservices and have a few basic architectural questions that I can't get solved right now. I'm using the Quarkus framework with the standard extensions like quarkus-resteasy and quarkus-rest-client for the realization.
The scenario:
I have an example of a "Persistence" service that I want to externally populate with data via a REST call in a dedicated Maven project.
@Path("/api/persistence")
@Products(MediaType.APPLICATION_JSON)
public class Persistence{
@Inject
EntityManager entityManager;
@POST
@Transactional
public Response create(PostDto postDto) {
Post post = toPostMapper.toResource(postDto);
entityManager.persist(post);
return Response.ok(postDto).status(201).build();
}
}
At the same time I would like to have a microservice DataGenerator which generates the corresponding data and passes it to the Persistence Service.
My problem : API sharing
Both services were created as Maven projects.
According to the tutorials I found the correct way would be to declare an interface (here called PersistenceApi) in the DataGenerator project like this
@Path("/api/persistence")
@Products(MediaType.APPLICATION_JSON)
@RegisterRestClient
public interface PersistenceApi {
@POST
@Transactional
public Response create(PostDto post) ;
}
This interface is then integrated into the DataGenerator service via @Inject, which leads to the following exemplary service.
@RequestScoped
@Path("/api/datagenerator")
@Products("application/json")
@Consumes("application/json")
public class DataGenerator{
@Inject
@RestClient
PersistenceApi persistenceApi
@POST
public void getPostExamplePostToPersistence() {
PostDto post = new PostDto();
post.setTitle("Find me in db in persistence-service")
persistenceApi.create(post);
}
}
I have the PersistenceService running locally on port 8181 and have added the following entry in the application.properties of the DataGenerator project so that the service can be found.
furnace.collection.item.service.PersistenceApi/mp-rest/url=http://localhost:8181
furnace.collection.item.service.PersistenceApi/mp-rest/scope=javax.inject.Singleton
I find it "wrong" to declare the interface in my DataGenerator, because at this point I don't notice when the api provided by the Persistence service changes. Accordingly one could come up with the idea to position the interface in the Persistence service, which is then implemented by my concrete Persistence implementation and leads to the following code.
@Path("/api/persistence")
@Products(MediaType.APPLICATION_JSON)
@RegisterRestClient
public class PersistenceApiImpl implements PersistenceApi {
@Inject
EntityManager entityManager;
@POST
@Transactional
public Response create(PostDto fruit) {
Post post = toPostMapper.toResource(fruit);
entityManager.persist(post);
return Response.ok(fruit).status(201).build();
}
}
In order to use them in my DataGenerator project, I would have to include the Persistence project as a dependency in my DataGenerator project, which sounds like a "monolith with extra steps" to me and therefore feels wrong in terms of "separation of concerns".
I have tried the following approach:
I created another Maven project called PersistenceApi which only contains the corresponding PersistenceApi. This PersistenceApi project was then included as a dependency in both the "Persistence" and "DataGenerator" projects. In the "Persistence"-Project I implement the service from the example above and try to address the corresponding interface in the "DataGenerator"-Project via @Inject.
Unfortunately this does not work. When I'm building the service, I get the message that the required dependency PersistenceApi, which I want to include via @Inject in the DataGenerator service, cannot be injected in the form of an UnsatisfiedResolutionException.
Now my questions:
- I don't see what I'm missing here. Could you help me?
- Is this kind of API-sharing with dedicated Api projects a viable way or is the "monolith with extra steps" approach really the way to go?
Thank you in advance.
