Can't I expose a concrete class directly as a RESTful Service?
You definitely can. Have you tried it? It should work just fine.
Is that a bad practice?
Personally (and this is just my preference), I think it's bad practice to use interfaces. Some people may argue that it cleans up your code, but there are problems that come with using interfaces, for instance annotation inheritance can sometimes cause a problem for those who don't understand what the problem is. It can be really hard to spot.
If your argument is that interfaces make code cleaner, I have a couple arguments.
(1) Your code is less understandable. You need to keep referring back to the interface to see what arguments are for (e.g. inspecting the method parameter annotations). It's easier when all the annotations are in the code your actually writing.
(2) Interfaces have no implementation, so you would still need to implement every class. I personally go with an abstract base class that will implement all the basic operations. For example
public abstract class AbstractResource<T extends BaseEntity> {
private final Repository<T> repository;
public AbstractResource(Repository<T> repository) {
this.repository = repository;
}
@GET
public List<T> getAll() {
return this.repository.findAll();
}
@GET
@Path("{id}")
public T getOne(@PathParam("id") long id) {
T result = this.repository.findOne(id);
if (result == null) {
throw new NotFoundException();
}
return result;
}
@POST
public Response create(T entity, @Context UriInfo uriInfo) {
T saved = this.repository.save(entity);
// BaseEntity should have an id property
long id = saved.getId();
URI createdUri = uriInfo.getAbsoluteUriBuilder()
.path(id).build();
return Response.created(createdUri).build();
}
}
You could do the same for @PUT and @DELET. The core functionality is the same for all resource collections. The only thing that would need to change is the Repository type. All your implementations could just extend it like
@Path("pets")
public class PetsResource extends AbstractResource<Pet> {
@Inject
public PetsResource(PetsRepository repository) {
super(repository);
}
}
This is much cleaner. You don't need to implement the same basic CRUD operations for your concrete resources. If you want to provide other resource methods in your concrete resource class, you can do so.
