Spring Reactive consume POST using FLUX or MONO

Question

How to consume a POST or PUT using Mono or Flux from method parameter. Let us say I've EmployeeApi interface defined as shown below, where creating a employee object using Mono

@RequestMapping("${v1Api}/employee")
public interface EmployeeApi {

    @GetMapping(produces = MediaType.APPLICATION_JSON_VALUE)
    Flux<ResponseEntity<Employee>> list();

    @PostMapping(consumes = MediaType.APPLICATION_JSON_VALUE)
    Mono<ResponseEntity<Void>> create(@Valid Mono<Employee> employee);
}

Implementation method.

    @Override
    public Mono<ResponseEntity<Void>> create(@Valid Mono<Employee> emp) {
        emp.doOnNext(e->System.out.println(e.getEmpId())); 
        return Mono.empty();
    }

Getting below error

 at [Source: (PushbackInputStream); line: 1, column: 1]
    at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67) ~[jackson-databind-2.9.8.jar:2.9.8]
    at com.fasterxml.jackson.databind.DeserializationContext.reportBadDefinition(DeserializationContext.java:1452) ~[jackson-databind-2.9.8.jar:2.9.8]
    at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1028) ~[jackson-databind-2.9.8.jar:2.9.8]
    at com.fasterxml.jackson.databind.deser.AbstractDeserializer.deserialize(AbstractDeserializer.java:265) ~[jackson-databind-2.9.8.jar:2.9.8]
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4013) ~[jackson-databind-2.9.8.jar:2.9.8]
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3084) ~[jackson-databind-2.9.8.jar:2.9.8]
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:239) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.read(AbstractJackson2HttpMessageConverter.java:227) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodArgumentResolver.readWithMessageConverters(AbstractMessageConverterMethodArgumentResolver.java:204) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.readWithMessageConverters(RequestResponseBodyMethodProcessor.java:157) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.resolveArgument(RequestResponseBodyMethodProcessor.java:130) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:126) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:166) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:134) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:800) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1038) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:908) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:660) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.boot.actuate.web.trace.servlet.HttpTraceFilter.doFilterInternal(HttpTraceFilter.java:90) ~[spring-boot-actuator-2.1.2.RELEASE.jar:2.1.2.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.filterAndRecordMetrics(WebMvcMetricsFilter.java:117) ~[spring-boot-actuator-2.1.2.RELEASE.jar:2.1.2.RELEASE]
    at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.doFilterInternal(WebMvcMetricsFilter.java:106) ~[spring-boot-actuator-2.1.2.RELEASE.jar:2.1.2.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:834) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1417) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_172]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_172]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.14.jar:9.0.14]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_172]

Though It can be done using ServerRequest object as shown below.

public Mono<ServerResponse> create(ServerRequest request) {
        Mono<Employee> emp= request.bodyToMono(Employee.class).doOnNext(e-> System.out.println(e.getEmpId()); 
        return ok().build(repository.save(emp));
}

But Is there a way to consume directly using Mono or Flux ?

Answer 1

The stacktrace shows that your application isn't using Spring WebFlux but actually Spring MVC. As explained in the reference documentation, Spring MVC only supports reactive types as return values, not as method arguments .

Also, note that the Flux<ResponseEntity<Employee>> doesn't make sense since a single endpoint cannot return several HTTP responses - Flux represents a 0..N cardinility; Mono is more appropriate in that case.