Error when I make request with Feign(feign.codec.DecodeException) - spring-boot

Question

When I make a Get request with Feign Client, I get the following error.
Request
UserRepresentation userByUserName = keycloakClient.getUserByUserName("tommy");
UserRepresentation class url
https://github.com/keycloak/keycloak/blob/main/core/src/main/java/org/keycloak/representations/idm/UserRepresentation.java
Rest api
#GetMapping("/users?username={userName}")
UserRepresentation getUserByUserName(#PathVariable(name = "userName") String userName);
Error
feign.codec.DecodeException: Error while extracting response for type [class org.keycloak.representations.idm.UserRepresentation] and content type [application/json]; nested exception is org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot deserialize value of type `org.keycloak.representations.idm.UserRepresentation` from Array value (token `JsonToken.START_ARRAY`); nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `org.keycloak.representations.idm.UserRepresentation` from Array value (token `JsonToken.START_ARRAY`)
at [Source: (org.springframework.util.StreamUtils$NonClosingInputStream); line: 1, column: 1]
at feign.InvocationContext.proceed(InvocationContext.java:40) ~[feign-core-11.10.jar:?]
at feign.AsyncResponseHandler.decode(AsyncResponseHandler.java:116) ~[feign-core-11.10.jar:?]
at feign.AsyncResponseHandler.handleResponse(AsyncResponseHandler.java:89) ~[feign-core-11.10.jar:?]
at feign.SynchronousMethodHandler.executeAndDecode(SynchronousMethodHandler.java:141) ~[feign-core-11.10.jar:?]
at feign.SynchronousMethodHandler.invoke(SynchronousMethodHandler.java:91) ~[feign-core-11.10.jar:?]
at feign.ReflectiveFeign$FeignInvocationHandler.invoke(ReflectiveFeign.java:100) ~[feign-core-11.10.jar:?]
at jdk.proxy2.$Proxy194.getUserByUserName(Unknown Source) ~[?:?]
at com.example.authentication.service.UserBusinessService.findUserByUserName(UserBusinessService.java:76) ~[classes/:?]
at com.example.authentication.service.UserBusinessService.resetPassword(UserBusinessService.java:182) ~[classes/:?]
at com.example.authentication.rest.impl.UserServiceImpl.resetUserPassword(UserServiceImpl.java:113) ~[classes/:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77) ~[?:?]
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]
at java.lang.reflect.Method.invoke(Method.java:568) ~[?:?]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) ~[spring-web-5.3.23.jar:5.3.23]
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150) ~[spring-web-5.3.23.jar:5.3.23]
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117) ~[spring-webmvc-5.3.23.jar:5.3.23]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.3.23.jar:5.3.23]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.23.jar:5.3.23]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.23.jar:5.3.23]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1071) ~[spring-webmvc-5.3.23.jar:5.3.23]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:964) ~[spring-webmvc-5.3.23.jar:5.3.23]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.23.jar:5.3.23]
at org.springframework.web.servlet.FrameworkServlet.doPut(FrameworkServlet.java:920) ~[spring-webmvc-5.3.23.jar:5.3.23]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:684) ~[tomcat-embed-core-9.0.65.jar:4.0.FR]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.23.jar:5.3.23]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:764) ~[tomcat-embed-core-9.0.65.jar:4.0.FR]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.65.jar:9.0.65]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at com.example.framework.security.filter.PermissionFilter.doFilterInternal(PermissionFilter.java:60) ~[security-0.0.1-SNAPSHOT.jar:?]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at com.example.framework.security.filter.LogContextFilter.doFilterInternal(LogContextFilter.java:22) ~[security-0.0.1-SNAPSHOT.jar:?]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at com.example.framework.security.filter.SecurityFilter.doFilterInternal(SecurityFilter.java:69) ~[security-0.0.1-SNAPSHOT.jar:?]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:337) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:115) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:81) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:122) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:116) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:126) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:81) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:109) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:149) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.oauth2.server.resource.web.BearerTokenAuthenticationFilter.doFilterInternal(BearerTokenAuthenticationFilter.java:142) ~[spring-security-oauth2-resource-server-5.7.3.jar:5.7.3]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:103) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:89) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:117) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.header.HeaderWriterFilter.doHeadersAfter(HeaderWriterFilter.java:90) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:75) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:112) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:82) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:55) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.session.DisableEncodeUrlFilter.doFilterInternal(DisableEncodeUrlFilter.java:42) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:346) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:221) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:186) ~[spring-security-web-5.7.3.jar:5.7.3]
at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:354) ~[spring-web-5.3.23.jar:5.3.23]
at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:267) ~[spring-web-5.3.23.jar:5.3.23]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.23.jar:5.3.23]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.23.jar:5.3.23]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.23.jar:5.3.23]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:360) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:890) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1789) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
at java.lang.Thread.run(Thread.java:833) ~[?:?]
Caused by: org.springframework.web.client.RestClientException: Error while extracting response for type [class org.keycloak.representations.idm.UserRepresentation] and content type [application/json]; nested exception is org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot deserialize value of type `org.keycloak.representations.idm.UserRepresentation` from Array value (token `JsonToken.START_ARRAY`); nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `org.keycloak.representations.idm.UserRepresentation` from Array value (token `JsonToken.START_ARRAY`)
at [Source: (org.springframework.util.StreamUtils$NonClosingInputStream); line: 1, column: 1]
at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:120) ~[spring-web-5.3.23.jar:5.3.23]
at org.springframework.cloud.openfeign.support.SpringDecoder.decode(SpringDecoder.java:75) ~[spring-cloud-openfeign-core-3.1.5.jar:3.1.5]
at org.springframework.cloud.openfeign.support.ResponseEntityDecoder.decode(ResponseEntityDecoder.java:61) ~[spring-cloud-openfeign-core-3.1.5.jar:3.1.5]
at feign.optionals.OptionalDecoder.decode(OptionalDecoder.java:36) ~[feign-core-11.10.jar:?]
at feign.InvocationContext.proceed(InvocationContext.java:36) ~[feign-core-11.10.jar:?]
... 115 more
When I change the service like this, I don't get an error.
#GetMapping("/users?username={userName}")
ResponseEntity<Object> getUserByUserName(#PathVariable(name = "userName") String userName);
How can i solve the problem?

Answer 1

Apparently, the endpoint you call returns a collection of UserRepresentation and not a single value (... from Array value (token `JsonToken.START_ARRAY`) ...).
Have you tried with Collection<UserRepresentation> or List<UserRepresentation>?
#GetMapping("/users?username={userName}")
Collection<UserRepresentation> getUserByUserName(...);