Jersey fails to respond with wildcard generics

[mkarg]

Problem Description

Apparently Jersey 3.x has problems with serving wildcard generics.

Serving wildcard generics was working successfully on Jersey 2.x, and it still is working successfully on RESTeasy, so I assume it is a bug introduced by Jersey 3. I also do not see that the JAX-RS spec forbids wildcards.

Reproducer

When running the following code on Jersey, serving /a succeeds, while serving /b fails with status code 500.

package eu.headcrashing.jaxrsdoneright.sebootstrap;

import java.util.Set;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionStage;

import jakarta.ws.rs.ApplicationPath;
import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.SeBootstrap;
import jakarta.ws.rs.core.Application;

public class Reproducer {

    public static void main(String[] args) throws InterruptedException {
        SeBootstrap.start(App.class).thenAccept(instance -> {
            var actualConfig = instance.configuration();
            System.out.println("BaseURI: " + actualConfig.baseUri());
        });
        Thread.currentThread().join();
    }

    @ApplicationPath("")
    public static class App extends Application {
        public Set<Class<?>> getClasses() {
            return Set.of(Res.class);
        }
    }

    @Path("")
    public static class Res {
        @GET @Path("a")
        public CompletionStage<? extends String> a() {
            return CompletableFuture.completedStage("hello");
        }

        @GET @Path("b")
        public CompletionStage<String> b() {
            return CompletableFuture.completedStage("hello");
        }
    }
}

The failing GET /b tells us:

Mai 12, 2023 8:11:03 AM org.glassfish.jersey.internal.Errors logErrors
WARNUNG: The following warnings have been detected: WARNING: Return type, java.util.concurrent.CompletionStage<? extends java.lang.String>, of method, public java.util.concurrent.CompletionStage<? extends java.lang.String> eu.headcrashing.jaxrsdoneright.sebootstrap.Reproducer$Res.a(), is not resolvable to a concrete type.

...

Mai 12, 2023 8:11:09 AM org.glassfish.jersey.server.ServerRuntime$Responder process
WARNUNG: An exception mapping did not successfully produce and processed a response. Logging the exception propagated to the default exception mapper.
java.lang.IllegalArgumentException: Type parameter ? extends java.lang.String not a class or parameterized type whose raw type is a class
        at jakarta.ws.rs.core.GenericType.getClass(GenericType.java:173)
        at jakarta.ws.rs.core.GenericType.<init>(GenericType.java:132)
        at org.glassfish.jersey.message.internal.OutboundMessageContext.setEntityType(OutboundMessageContext.java:763)
        at org.glassfish.jersey.server.ContainerResponse.setEntityType(ContainerResponse.java:313)
        at org.glassfish.jersey.server.model.ResourceMethodInvoker.lambda$invoke$2(ResourceMethodInvoker.java:471)
        at org.glassfish.jersey.process.internal.Stages$LinkedStage.apply(Stages.java:284)
        at org.glassfish.jersey.process.internal.Stages.process(Stages.java:147)
        at org.glassfish.jersey.server.ServerRuntime$Responder.processResponse(ServerRuntime.java:383)
        at org.glassfish.jersey.server.ServerRuntime$Responder.process(ServerRuntime.java:375)
        at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:264)
        at org.glassfish.jersey.internal.Errors$1.call(Errors.java:248)
        at org.glassfish.jersey.internal.Errors$1.call(Errors.java:244)
        at org.glassfish.jersey.internal.Errors.process(Errors.java:292)
        at org.glassfish.jersey.internal.Errors.process(Errors.java:274)
        at org.glassfish.jersey.internal.Errors.process(Errors.java:244)
        at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:265)
        at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:240)
        at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:697)
        at org.glassfish.jersey.grizzly2.httpserver.GrizzlyHttpContainer.service(GrizzlyHttpContainer.java:367)
        at org.glassfish.grizzly.http.server.HttpHandler$1.run(HttpHandler.java:190)
        at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:535)
        at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:515)
        at java.base/java.lang.Thread.run(Unknown Source)

Mai 12, 2023 8:11:09 AM org.glassfish.jersey.server.ServerRuntime$Responder writeResponse
SCHWERWIEGEND: Error while closing the output stream in order to commit response.
java.lang.IllegalStateException: Illegal attempt to call getOutputStream() after getWriter() has already been called.
        at org.glassfish.grizzly.http.server.Response.getNIOOutputStream(Response.java:578)
        at org.glassfish.grizzly.http.server.Response.getOutputStream(Response.java:602)
        at org.glassfish.jersey.grizzly2.httpserver.GrizzlyHttpContainer$ResponseWriter.writeResponseStatusAndHeaders(GrizzlyHttpContainer.java:250)
        at org.glassfish.jersey.server.ServerRuntime$Responder$1.getOutputStream(ServerRuntime.java:667)
        at org.glassfish.jersey.message.internal.CommittingOutputStream.commitStream(CommittingOutputStream.java:171)
        at org.glassfish.jersey.message.internal.CommittingOutputStream.flushBuffer(CommittingOutputStream.java:276)
        at org.glassfish.jersey.message.internal.CommittingOutputStream.commit(CommittingOutputStream.java:232)
        at org.glassfish.jersey.message.internal.CommittingOutputStream.close(CommittingOutputStream.java:247)
        at org.glassfish.jersey.message.internal.OutboundMessageContext.close(OutboundMessageContext.java:865)
        at org.glassfish.jersey.server.ContainerResponse.close(ContainerResponse.java:389)
        at org.glassfish.jersey.server.ServerRuntime$Responder.writeResponse(ServerRuntime.java:749)
        at org.glassfish.jersey.server.ServerRuntime$Responder.processResponse(ServerRuntime.java:385)
        at org.glassfish.jersey.server.ServerRuntime$Responder.processResponseWithDefaultExceptionMapper(ServerRuntime.java:633)
        at org.glassfish.jersey.server.ServerRuntime$Responder.process(ServerRuntime.java:458)
        at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:269)
        at org.glassfish.jersey.internal.Errors$1.call(Errors.java:248)
        at org.glassfish.jersey.internal.Errors$1.call(Errors.java:244)
        at org.glassfish.jersey.internal.Errors.process(Errors.java:292)
        at org.glassfish.jersey.internal.Errors.process(Errors.java:274)
        at org.glassfish.jersey.internal.Errors.process(Errors.java:244)
        at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:265)
        at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:240)
        at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:697)
        at org.glassfish.jersey.grizzly2.httpserver.GrizzlyHttpContainer.service(GrizzlyHttpContainer.java:367)
        at org.glassfish.grizzly.http.server.HttpHandler$1.run(HttpHandler.java:190)
        at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:535)
        at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:515)
        at java.base/java.lang.Thread.run(Unknown Source)

[jansupol]

1. It does not seem to work in 2.x
2. I assume serving /a fails while serving /b passes
3. It is a corner-case
4. The support for this (I assume a new feature) is implementable

[mkarg]

1. It works pretty well on Payara 5, which is based on Jersey 2.
2. Yes.
3. So what?
4. As we are using it in production on Payara 5, hence Jersey 2, it cannot be a new feature but actually making it work again.
5. It works pretty well on RESTeasy.

[mkarg]

I confirm that I cannot reproduce the bug anymore using Jersey v. 3.1.5.payara-p1 as part of Payara 6.2024.3.

I assume that earlier and non-payara-specific versions do contain the same fix, but I did not find the time to test them.