open-liberty and openapi(/ui) and "no operations defined in spec!" - openapi

Question

I can not find out why my rest api endpoints are not visible / executable in openapi/ui with openliberty. openapi/ui reports "there are no operations defined in spec!" My project consists of an empty application class and a trivial rest controller with a single endpoint:
package sandbox.io.rest;
import jakarta.ws.rs.ApplicationPath;
import jakarta.ws.rs.core.Application;
#ApplicationPath("/api")
public class RestApplication extends Application { }
package sandbox.io.rest;
import static jakarta.ws.rs.core.MediaType.APPLICATION_JSON;
import jakarta.enterprise.context.ApplicationScoped;
import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.Produces;
import jakarta.ws.rs.core.Response;
#ApplicationScoped
public class RestController
{
#GET
#Path("/system/properties")
#Produces(APPLICATION_JSON)
public Response getSystemProperties()
{
return Response.ok(System.getProperties()).build();
}
}
I have the following features activated in my server.xml:
<featureManager>
<feature>jakartaee-9.1</feature>
<feature>microProfile-5.0</feature>
<!-- <feature>restfulWS-3.0</feature> -->
<!-- <feature>jsonp-2.0</feature> -->
<!-- <feature>jsonb-2.0</feature> -->
<!-- <feature>cdi-3.0</feature> -->
<!-- <feature>mpConfig-3.0</feature> -->
<!-- <feature>mpRestClient-3.0</feature> -->
<!-- <feature>mpOpenAPI-3.0</feature> -->
</featureManager>
Everything was generated from openliberty/get started.
There is a real minimal reproducer here.
I also played around with activation of mpOpenAPI-3.0 feature but could not make it work. Could anybody have a look at the reproducer please?
BTW: Please don't get irritated by the repo name, it's just that I try to set up an environment for openliberty, hibernate and postgres ... However I'd like to use openapi/ui, too.

Answer 1

In addition to Scott Kurz's answer: https://stackoverflow.com/a/71946440/8067386
The reason OpenAPI isn't finding the endpoint is because without the #PATH annotation (or #Provider) your RestController class is not being registered with the JAX-RS runtime. An older way to register would be to return RestController.class from RestApplication.getClasses(). However, this is less dynamic than annotating your endpoint class.

Answer 2

You can fix this by adding a class-level #Path annotation. To keep the aggregate URL path the same you can do #Path("/") so:
#Path("/")
#ApplicationScoped
public class RestController
{
#GET
#Path("/system/properties")
#Produces(APPLICATION_JSON)
public Response getSystemProperties()
{
return Response.ok(System.getProperties()).build();
}
}
I believe this is more a Jakarta RESTful issue than an MicroProfile OpenAPI issue as it turns out.