無法將聯系人投射到org.springframework.core.io.support.ResourceRegion

Question

我目前在我們的應用中面臨新問題。

使用方法：

• springboot 2

• Java JDK-9.0.4

• jpa，休眠

• IDE =想法

• 作業系統：MacOS

問題 ：當我嘗試在前端窗口（位於Thymeleaf內部）中以select2形式找到聯系人（Contact是具有以下名稱的實體類：名稱，姓氏，電話，地址）時，我收到錯誤消息：

java.lang.ClassCastException: xx.yy.zz.Contact cannot be cast to org.springframework.core.io.support.ResourceRegion.
at org.springframework.http.converter.ResourceRegionHttpMessageConverter.writeInternal(ResourceRegionHttpMessageConverter.java:136) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.http.converter.AbstractGenericHttpMessageConverter.write(AbstractGenericHttpMessageConverter.java:102) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:271) ~[spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:182) ~[spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:82) ~[spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:119) ~[spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:870) ~[spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:776) ~[spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:991) ~[spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925) ~[spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:978) [spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:870) [spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:635) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:855) [spring-webmvc-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) [tomcat-embed-websocket-8.5.28.jar:8.5.28]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:320) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:127) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:91) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:119) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:137) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.authentication.rememberme.RememberMeAuthenticationFilter.doFilter(RememberMeAuthenticationFilter.java:158) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:170) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.session.ConcurrentSessionFilter.doFilter(ConcurrentSessionFilter.java:155) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:200) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:116) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:100) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:66) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:105) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:215) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:178) [spring-security-web-5.0.3.RELEASE.jar:5.0.3.RELEASE]
at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:357) [spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:270) [spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) [spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:109) [spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81) [spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) [spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.4.RELEASE.jar:5.0.4.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:496) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459) [tomcat-embed-core-8.5.28.jar:8.5.28]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.28.jar:8.5.28]
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167) [na:na]
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641) [na:na]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.28.jar:8.5.28]
at java.base/java.lang.Thread.run(Thread.java:844) [na:na]

---

這是請求映射，當我嘗試在select2中查找某些聯系人時使用。

@RequestMapping(method = GET)
@ResponseBody
public List<Object> findIt(@RequestParam(name = "query", defaultValue = "") String query) {
    Map<GroupKey, List<Contact>> groupedContacts = contactRepository.findItByQuery(query)
            .stream()
            .collect(groupingBy(contact -> new GroupKey(contact)));

    return groupedContacts.entrySet()
            .stream()
            .map(entry -> {
                GroupKey key = entry.getKey();
                List<Contact> contacts = entry.getValue();

                if (contacts.size() == 1) {
                    return contacts.get(0);
                } else {
                    return new Group(key.toString(), contacts);
                }
            })
            .collect(toList());
     }

---

在調查期間，我無法找到問題的答案。 什么是資源區域：資源實現的區域，由資源中的位置和該區域的長度的字節數實現。 。

問題0 ：為什么需要從聯系人投射到ResourceGroup？

問題1 ：為什么現在無法進行這種轉換？

---

在您否決這個問題之前，請告訴我原因。 謝謝！

Answer 1

發生這種情況是因為您的應用程序找不到有效的HttpMessageConverter來將對象轉換為JSON，並且默認為ResourceRegion轉換器（默認為八位字節流響應），請嘗試執行以下操作：

@Configuration
@EnableWebMvc
public class WebServicesConfig implements WebMvcConfigurer {
    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        MappingJackson2HttpMessageConverter jsonConverter = new MappingJackson2HttpMessageConverter();   
        jsonConverter.setSupportedMediaTypes(Collections.singletonList(MediaType.APPLICATION_JSON));
        converters.add(jsonConverter);
    }
}