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ClassCastException with Kotlin function #1101

Closed sryze closed 10 months ago

sryze commented 10 months ago

Describe the bug

I have a function written in Kotlin similar to this:

@SpringBootApplication
open class DemoKotlinApplication {
    @Bean
    fun uppercase(): (String) -> String {
        return { it.toUpperCase() }
    }
}

and it always fails when I call it via its URL e.g. localhost:8080/uppercase

java.lang.ClassCastException: class org.springframework.cloud.function.context.config.CoroutinesUtils$invokeSuspendingSupplier$1 cannot be cast to class java.lang.String (org.springframework.cloud.function.context.config.CoroutinesUtils$invokeSuspendingSupplier$1 is in unnamed module of loader 'app'; java.lang.String is in module java.base of loader 'bootstrap')
    at com.example.kotlin.DemoKotlinApplication$uppercase$1.invoke(DemoKotlinApplication.kt:11) ~[classes/:na]
    at org.springframework.cloud.function.context.config.CoroutinesUtils$invokeSuspendingSupplier$1.invokeSuspend(CoroutinesUtils.kt:105) ~[spring-cloud-function-context-4.1.0.jar:4.1.0]
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33) ~[kotlin-stdlib-1.9.20.jar:1.9.255-SNAPSHOT]
    at kotlinx.coroutines.internal.DispatchedContinuationKt.resumeCancellableWith(DispatchedContinuation.kt:367) ~[kotlinx-coroutines-core-jvm-1.7.3.jar:na]
    at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable(Cancellable.kt:30) ~[kotlinx-coroutines-core-jvm-1.7.3.jar:na]
    at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable$default(Cancellable.kt:25) ~[kotlinx-coroutines-core-jvm-1.7.3.jar:na]
    at kotlinx.coroutines.CoroutineStart.invoke(CoroutineStart.kt:110) ~[kotlinx-coroutines-core-jvm-1.7.3.jar:na]
    at kotlinx.coroutines.AbstractCoroutine.start(AbstractCoroutine.kt:126) ~[kotlinx-coroutines-core-jvm-1.7.3.jar:na]
    at kotlinx.coroutines.reactor.MonoKt.monoInternal$lambda$2(Mono.kt:92) ~[kotlinx-coroutines-reactor-1.7.3.jar:na]
    at reactor.core.publisher.MonoCreate.subscribe(MonoCreate.java:61) ~[reactor-core-3.6.0.jar:3.6.0]
    at reactor.core.publisher.Mono.subscribe(Mono.java:4512) ~[reactor-core-3.6.0.jar:3.6.0]
    at org.springframework.web.servlet.mvc.method.annotation.ReactiveTypeHandler$DeferredResultSubscriber.connect(ReactiveTypeHandler.java:465) ~[spring-webmvc-6.1.1.jar:6.1.1]
    at org.springframework.web.servlet.mvc.method.annotation.ReactiveTypeHandler.handleValue(ReactiveTypeHandler.java:163) ~[spring-webmvc-6.1.1.jar:6.1.1]
    at org.springframework.web.servlet.mvc.method.annotation.ResponseBodyEmitterReturnValueHandler.handleReturnValue(ResponseBodyEmitterReturnValueHandler.java:154) ~[spring-webmvc-6.1.1.jar:6.1.1]
    at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:78) ~[spring-web-6.1.1.jar:6.1.1]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:136) ~[spring-webmvc-6.1.1.jar:6.1.1]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:917) ~[spring-webmvc-6.1.1.jar:6.1.1]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:829) ~[spring-webmvc-6.1.1.jar:6.1.1]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-6.1.1.jar:6.1.1]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089) ~[spring-webmvc-6.1.1.jar:6.1.1]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979) ~[spring-webmvc-6.1.1.jar:6.1.1]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014) ~[spring-webmvc-6.1.1.jar:6.1.1]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903) ~[spring-webmvc-6.1.1.jar:6.1.1]
    at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564) ~[tomcat-embed-core-10.1.16.jar:6.0]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885) ~[spring-webmvc-6.1.1.jar:6.1.1]
    at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658) ~[tomcat-embed-core-10.1.16.jar:6.0]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:205) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51) ~[tomcat-embed-websocket-10.1.16.jar:10.1.16]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-6.1.1.jar:6.1.1]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.1.jar:6.1.1]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-6.1.1.jar:6.1.1]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.1.jar:6.1.1]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-6.1.1.jar:6.1.1]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.1.jar:6.1.1]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:482) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:115) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:340) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:391) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:896) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1744) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-10.1.16.jar:10.1.16]
    at java.base/java.lang.Thread.run(Thread.java:833) ~[na:na]

But a function taking no arguments works fine, for example:

@Bean
fun dummy(): () -> String {
    return { "hello" }
}

Sample

https://github.com/spring-cloud/spring-cloud-function/tree/main/spring-cloud-function-samples/function-sample-kotlin-web

sryze commented 10 months ago

BTW the documentation at https://docs.spring.io/spring-cloud-function/reference/spring-cloud-function/programming-model.html#kotlin-lambda-support forgets to mention that one needs to add spring-cloud-function-kotlin to dependencies to pull the couroutines libraries, otherwise a different error occurs: java.lang.ClassNotFoundException: kotlinx.coroutines.Dispatcher (even if one does not define them as suspending functions, which I personally thought was a little strange)

sryze commented 10 months ago

Never mind. I forgot to pass an argument to the function, that's why it wasn't working.

But it would be great if SCF could produce a more helpful exception message.