Config generated classes are not registered for reflection

[vsevel]

Description

In ConfigMapping we define interfaces such as com.acme.config.MyConfig. At build time this generates implementation classes such as com.acme.config.MyConfig-<hash>Impl

If you intend to use those classes through reflection, you end up having to figure out the hash that has been generated, and add @RegisterForReflection(classNames= {com.acme.config.MyConfig-1234Impl}) into your application.

In our project, we are adding the config objects into freemarker template models, and access some of the config properties from within the templates, hence the need for reflection.

Ideally those config implementation classes should be enabled for reflection, or at least (if we believe the need is rare, and/or if we fear the impact on the native exec) the application should be offered an easy way to enable those classes for reflection.

see zulip conversation

/cc @radcortez

Implementation ideas

One option would be to allow adding @RegisterForReflection on the config interfaces, which would be interpreted as: a registration on the config impl classes need to be done.

Another option would be to add a build time parameter register-config-classes-for-reflection/serialization.

[quarkus-bot]

You added a link to a Zulip discussion, please make sure the description of the issue is comprehensive and doesn't require accessing Zulip.

This message is automatically generated by a bot.

[vsevel]

to reproduce:

package org.acme.getting.started;

import io.smallrye.config.ConfigMapping;

@ConfigMapping(prefix = "job")
public interface JobConfig {

    String hello();
}

@Path("/hello")
public class GreetingResource {

    private static final Logger log = LoggerFactory.getLogger(GreetingResource.class);

    @Inject
    JobConfig job;

    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public String hello() {
        try {
            Method helloMethod = job.getClass().getDeclaredMethod("hello");
            return (String) helloMethod.invoke(job);
        } catch (Exception e) {
            return e.toString();
        }
    }
}

application.properties:

job.hello=world

@QuarkusTest
public class GreetingResourceTest {

    @Test
    public void testHelloEndpoint() {
        given()
          .when().get("/hello")
          .then()
             .statusCode(200)
             .body(is("world"));
    }
}

Build and start in native mode, and invoke the hello endpoint (works in jvm mode):

curl http://localhost:8090/hello
java.lang.NoSuchMethodException: org.acme.getting.started.JobConfig-1625885570Impl.hello()

[radcortez]

Sounds reasonable. I'll add a better way to do this.

[vsevel]

let me know if I can help.

[radcortez]

Thanks, no worries. It is a fairly easy change.