如何在JAX-RS中处理多个子资源？

Question

I have a JAX-RS REST API with several sub resources eg

users/{user_id}/posts/{post_id}/comments/{comment_id} . The resources are divided into individual classes ( UsersResource , UserResource , PostsResource , etc.) and accessed via sub resource locators. Each resource uses a correlating service ( UserService , PostService , CommentService ) to access the database.

How would I go about realising this? I tried to search for an example but was only able to find very basic ones.

I already implemented several approaches but they all "feel" wrong.

One was to inject all services in the root resource and pass them along. But it seems wasteful to instantiate all services although only the first might be needed.

Another was to make all resources @RequestScoped and inject the subsequent resource so the right service can be injected at the right place. But I would need to inject the sub resource in advance even if I didn't need it and I wouldn't be able to pass parameters along.

My current approach fails at not being able to inject the service inside my sub resource. (see below)

root resource (resources/users)

@RequestScoped
@Path("users")
public class UsersResource() {

    @Inject
    private UserService service;

    @Path("{user_id}")
    public UserResource getUserResource(@Context ResourceContext context, @PathParam("user_id") Long id) {
        User entity = this.service.find(id);

        if (entity == null)
            throw new WebApplicationException(Response.status(Status.NOT_FOUND).build());

        return context.initResource(new UserResource(entity, this.service));
    }
}

user sub resource (resources/users/{user_id})

public class UserResource() {

    private User entity;
    private UserService service;

    public UserResource(User entity, UserService service) {
        this.entity = entity;
        this.service = service;
    }

    @GET
    public Response doGet() {
        return Response.ok(entity).build();
    }

    @Path("posts")
    public TodosResource getPostsResource(@Context ResourceContext context) {
        return context.initResource(new PostsResource(entity));
    }
}

posts sub resource (resources/users/{user_id}/posts)

public class PostsResource() {

    @Inject // can't inject here
    private PostService service;

    private User user;

    public PostsResource(User user) {
        this.user = user;
    }

    @POST
    public Response doPost(@Context UriInfo info, Post post) {
        post.setUser(this.user);
        Post entity = this.service.persist(post);
        URI uri = info.getAbsolutePathBuilder().path("/" + entity.getId()).build();

        return Response.created(uri).entity(entity).build();
    }

    @Path("{post_id}")
    public PostResource getpostResource(@Context ResourceContext context, @PathParam("post_id") Long id) {
        Post entity = this.service.find(id);

        if (entity == null)
            throw new WebApplicationException(Response.status(Status.NOT_FOUND).build());

        return context.initResource(new PostResource(entity));
    }

service example

@Stateless
public class UserService {

    @PersistenceContext
    private EntityManager em;

    (...)
}

Answer 1

Maybe a bit late, but the answer to this is still hard to find.

To Inject EJBs directly in subresources, annotate the subresource with @Provider, it could also be a good idea to append @Produces.

So your

public class PostsResource() {

becomes

@Provider
@Produces(MediaType.APPLICATION_JSON)
public class PostsResource() {