Kotlin > Spring Boot > Using router DSL, POST Method body, unable to convert JSON to POJOs

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1

I’m trying to build a Petstore Fullstack application using Kotlin Multiplatform. I’m using Spring Router DSL for defining rest endpoints. For the GET method, it worked fine. Then I started working on POST, below is the code I wrote for the POST method

   (accept(APPLICATION_JSON) and "/api").nest {
        POST("/newPet") {ok().body(petHandler::newPet)}
    }

PetHandler.kt

@Component
class PetHandler(val petRepo: PetRepo) {
        fun newPet(request: ServerRequest): Pets {
            val pet = request.body<Pets>()
            return petRepo.save(pet)
       }
}

but then, when I hit the POST API i got below exception,

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class kotlin.reflect.jvm.internal.ReflectProperties$LazyVal and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: org.kotlinhyd.petstore.routes.PetStoreRouter$apiRouter$1$1$3$1["owner"]->kotlin.reflect.jvm.internal.KClassImpl["data"])
	at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:77) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.SerializerProvider.reportBadDefinition(SerializerProvider.java:1191) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.DatabindContext.reportBadDefinition(DatabindContext.java:404) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.failForEmpty(UnknownSerializer.java:71) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.serialize(UnknownSerializer.java:33) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:722) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:166) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:722) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:166) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:319) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.ObjectWriter$Prefetch.serialize(ObjectWriter.java:1433) ~[jackson-databind-2.10.3.jar:2.10.3]
	at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:921) ~[jackson-databind-2.10.3.jar:2.10.3]
	at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:287) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.http.converter.AbstractGenericHttpMessageConverter.write(AbstractGenericHttpMessageConverter.java:104) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.web.servlet.function.DefaultEntityResponseBuilder$DefaultEntityResponse.writeEntityWithMessageConverters(DefaultEntityResponseBuilder.java:308) ~[spring-webmvc-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.web.servlet.function.DefaultEntityResponseBuilder$DefaultEntityResponse.writeToInternal(DefaultEntityResponseBuilder.java:270) ~[spring-webmvc-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.web.servlet.function.DefaultServerResponseBuilder$AbstractServerResponse.writeTo(DefaultServerResponseBuilder.java:298) ~[spring-webmvc-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.web.servlet.function.support.HandlerFunctionAdapter.handle(HandlerFunctionAdapter.java:77) ~[spring-webmvc-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040) ~[spring-webmvc-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) ~[spring-webmvc-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909) ~[spring-webmvc-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:660) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.33.jar:9.0.33]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.5.RELEASE.jar:5.2.5.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1594) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[na:na]
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[na:na]
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.33.jar:9.0.33]
	at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]

You can find full project configuration in this GitHub repo Kotlin-Petstore-Project

Here is the JSON request i’m using for calling the api

{
	"name": "tom",
	"petType": "Cat",
	"petSubType": "Maine Coon",
	"numberOfPetsAvailable": "2",
	"tags": "friendly",
	"petImageUrl": ""
}

Can you please help me to solve this issue.
Thanks in Advance.

2

Not sure, but maybe you miss Jackson Kotlin support in your project dependencies ?

In all cases, it looks more like a Jackson / Spring interop problem. Maybe you’ll get more useful insights by asking directly to one of these communities.

3 Likes
3

Thank you very much @alexis.manin, I’ll ask them as well.

4

After trying different methods and debugging into the framework, the solution I found was simple, I just changed the method reference to the normal method call, below is the updated code in the router

@Bean
fun apiRouter() = router {
        (accept(APPLICATION_JSON) and "/api").nest {
            POST("/newPet") { ok().body(petHandler.newPet(it))}
        }
}

Not sure why it solved, but while debugging the framework I found that wrong class resolved as DTO, but when I used regular method call Jackson framework properly converted DTO to JSON.

5

Sorry, totally missed that in your first post.

Your updated example works properly because you pass the result of newPet function as parameter.
In your original post, you gave a method handle (pointer): petHandler::newPet.

It means that body function received the definition of a lambda as parameter, and was asking Jackson to serialize the lambda itself, not to call the method and then serialize the result.

2 Likes
6

Understood the Logic @alexis.manin, Thank you for the explanation.