Spring Boot Kotlin Jersey ModelValidationException

Question

I am trying to get Spring Boot + Jersey working with Kotlin. I configured the way I typically would in Java but getting a the following stacktrace. It seems to indicate the controller is being instantiated twice but it shouldn't.

Here is my JerseyConfig class:

package com.joescodeshack.igdb.config

import com.fasterxml.jackson.module.kotlin.KotlinModule
import com.joescodeshack.igdb.controller.GenreController
import org.glassfish.jersey.server.ResourceConfig
import org.springframework.context.annotation.Bean
import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder
import org.springframework.stereotype.Component
import javax.ws.rs.ApplicationPath

@Component
@ApplicationPath("/api")
open class JerseyConfig : ResourceConfig {

    constructor() {
        register(GenreController());
    }

    @Bean
    open fun objectMapperBuilder(): Jackson2ObjectMapperBuilder
            = Jackson2ObjectMapperBuilder().modulesToInstall(KotlinModule())
}

GenreController (JAX-RS endpoint)

package com.joescodeshack.igdb.controller

import com.joescodeshack.igdb.domain.Genre
import javax.ws.rs.GET
import javax.ws.rs.Path
import javax.ws.rs.Produces
import javax.ws.rs.core.MediaType
import javax.ws.rs.core.Response

@Path("/genre")
open class GenreController {

    val genres : List<Genre> = listOf(Genre(1,"Butt"), Genre(2, "Cow"))

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    open fun getGenres() : Response {
        return Response.ok(genres).build();
    }
}

Stacktrace:

2016-09-06 15:26:26.529 ERROR 17332 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[.[.j.i.c.JerseyConfig]    : Allocate exception for servlet com.joescodeshack.igdb.config.JerseyConfig

org.glassfish.jersey.server.model.ModelValidationException: Validation of the application resource model has failed during application initialization.
[[FATAL] A resource model has ambiguous (sub-)resource method for HTTP method GET and input mime-types as defined by"@Consumes" and "@Produces" annotations at Java methods public javax.ws.rs.core.Response com.joescodeshack.igdb.controller.GenreController.getGenres() and public final java.util.List com.joescodeshack.igdb.controller.GenreController.getGenres() at matching regular expression /genre. These two methods produces and consumes exactly the same mime-types and therefore their invocation as a resource methods will always fail.; source='org.glassfish.jersey.server.model.RuntimeResource@1b6cce78']
    at org.glassfish.jersey.server.ApplicationHandler.initialize(ApplicationHandler.java:555) ~[jersey-server-2.23.1.jar:na]
    at org.glassfish.jersey.server.ApplicationHandler.access$500(ApplicationHandler.java:184) ~[jersey-server-2.23.1.jar:na]
    at org.glassfish.jersey.server.ApplicationHandler$3.call(ApplicationHandler.java:350) ~[jersey-server-2.23.1.jar:na]
    at org.glassfish.jersey.server.ApplicationHandler$3.call(ApplicationHandler.java:347) ~[jersey-server-2.23.1.jar:na]
    at org.glassfish.jersey.internal.Errors.process(Errors.java:315) ~[jersey-common-2.23.1.jar:na]
    at org.glassfish.jersey.internal.Errors.process(Errors.java:297) ~[jersey-common-2.23.1.jar:na]
    at org.glassfish.jersey.internal.Errors.processWithException(Errors.java:255) ~[jersey-common-2.23.1.jar:na]
    at org.glassfish.jersey.server.ApplicationHandler.<init>(ApplicationHandler.java:347) ~[jersey-server-2.23.1.jar:na]
    at org.glassfish.jersey.servlet.WebComponent.<init>(WebComponent.java:392) ~[jersey-container-servlet-core-2.23.1.jar:na]
    at org.glassfish.jersey.servlet.ServletContainer.init(ServletContainer.java:177) ~[jersey-container-servlet-core-2.23.1.jar:na]
    at org.glassfish.jersey.servlet.ServletContainer.init(ServletContainer.java:369) ~[jersey-container-servlet-core-2.23.1.jar:na]
    at javax.servlet.GenericServlet.init(GenericServlet.java:158) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1194) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:806) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:133) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:108) [tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:522) [tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) [tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349) [tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:1110) [tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:785) [tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1425) [tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.4.jar:8.5.4]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_102]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_102]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.4.jar:8.5.4]
    at java.lang.Thread.run(Thread.java:745) [na:1.8.0_102]

Answer 1

The problem is that the following property:

val genres : List<Genre> = listOf(Genre(1,"Butt"), Genre(2, "Cow"))

Generates a method that on JVM level has a following signature:

@NotNull
public final List<Genre> getGenres()

As you can see it conflicts with the other method in your controller. To resolve it change the property to be private or rename one of the methods.

PS. The error message is pretty clear about the problem:

public javax.ws.rs.core.Response com.joescodeshack.igdb.controller.GenreController.getGenres() and public final java.util.List com.joescodeshack.igdb.controller.GenreController.getGenres() at matching regular expression /genre. These two methods produces and consumes exactly the same mime-types and therefore their invocation as a resource methods will always fail.;