Question

我正在使用Spring Boot 2.0.3，Spring Data REST，Spring HATEOAS，Hibernate。我遇到了一个奇怪的问题，有时会在特定条件下发生。

我正在从Angular应用程序中调用REST端点，有时由于杰克逊在响应创建过程中引发的异常而导致调用失败。

我有一个@RepositoryRestController，由Angular应用程序调用（这是在某个时候引发异常的端点）：

@RepositoryRestController
@PreAuthorize("isAuthenticated()")
public class FrameController {

 @PostMapping(path = "/frames/{property}/groupBy")
    public ResponseEntity<?> groupByProperty(@PathVariable("property") String property, @RequestBody(required = true) List<Filter> filters, Pageable pageable) {
        Page<String> pageResult = frameService.groupByProperty(property, filters, pageable);
        log.info("Grouped result, size:{},total results: {},  {}", pageResult.getSize(), pageResult.getTotalElements(), pageResult.getContent());

        return ResponseEntity.ok(pagedResourcesAssembler.toResource(pageResult, stringResourceAssembler));
    }
}

这是从控制器调用的服务：

@Service
@Transactional
@PreAuthorize("isAuthenticated()")
public class FrameService {

 public Page<String> groupByProperty(@NotNull String property, @NotNull List<Filter> filters, Pageable pageable) {
        String where = "WHERE 1=1";
        String groupBy = " GROUP BY " + property;

       //BUILDING QUERY HERE

        TypedQuery<String> query = entityManager.createQuery("SELECT CAST(" + property + " as string) FROM Frame f " + where + groupBy + orderBy, String.class);
        TypedQuery<Long> queryCount = entityManager.createQuery("SELECT COUNT(*) FROM Frame f " + where + groupBy, Long.class);

        /**
         * 3. SETTING REAL VALUES IN THE QUERY
         */
        //SETTING PARAMETERS HERE

        /**
         * 4. PAGINATION
         */
        query.setFirstResult((int) pageable.getOffset());
        query.setMaxResults(pageable.getPageSize());
        long totalResult = queryCount.getResultList().size();

        return AppUtils.listToPageable(query.getResultList(), pageable, totalResult);
    }
}

该服务每次都有效，在那里我再也没有例外。

我还要公开一个RestRepository：

@Transactional
@PreAuthorize("isAuthenticated()")
public interface ContactRepository extends JpaRepository<Contact, Long> {

 @Query(value = "SELECT c FROM Contact c WHERE :searchString IS NULL OR (companyName LIKE CONCAT(:searchString,'%')) OR (CONCAT(lastName,' ',firstName) LIKE CONCAT(:searchString,'%'))")
    public Page<Contact> autocomplete(@Param("searchString") String searchString, Pageable pageable);

}

经过大量测试，我发现只有在调用端点autocomplete of ContactRepository之前调用端点/frames/{property}/groupBy时才会引发我要显示的异常。

这是我得到的例外：

14/12/2018 09:51:58,550  INFO http-nio-8082-exec-5 FrameController:110 - Grouped result, size:40,total results: 8,  [47, 49, 50, 51, 52, 53, 55, 58]
14/12/2018 09:51:58,560 ERROR http-nio-8082-exec-5 ApplicationExceptionHandler:133 - 
org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: (was java.lang.NullPointerException); nested exception is com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: org.springframework.hateoas.PagedResources["_embedded"])
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:296) ~[spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.http.converter.AbstractGenericHttpMessageConverter.write(AbstractGenericHttpMessageConverter.java:102) ~[spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:272) ~[spring-webmvc-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor.handleReturnValue(HttpEntityMethodProcessor.java:224) ~[spring-webmvc-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:82) ~[spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.hateoas.mvc.ResourceProcessorHandlerMethodReturnValueHandler.handleReturnValue(ResourceProcessorHandlerMethodReturnValueHandler.java:114) ~[spring-hateoas-0.24.0.RELEASE.jar:?]
    at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:82) ~[spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:119) ~[spring-webmvc-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:877) ~[spring-webmvc-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:783) ~[spring-webmvc-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:991) [spring-webmvc-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925) [spring-webmvc-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:974) [spring-webmvc-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:877) [spring-webmvc-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:661) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:851) [spring-webmvc-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) [tomcat-embed-websocket-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:101) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:101) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at cloud.test.server.filters.StoreFilter.doFilterInternal(StoreFilter.java:34) [classes/:?]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.filterAndRecordMetrics(WebMvcMetricsFilter.java:158) [spring-boot-actuator-2.0.3.RELEASE.jar:2.0.3.RELEASE]
    at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.filterAndRecordMetrics(WebMvcMetricsFilter.java:126) [spring-boot-actuator-2.0.3.RELEASE.jar:2.0.3.RELEASE]
    at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.doFilterInternal(WebMvcMetricsFilter.java:111) [spring-boot-actuator-2.0.3.RELEASE.jar:2.0.3.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.springframework.boot.actuate.web.trace.servlet.HttpTraceFilter.doFilterInternal(HttpTraceFilter.java:90) [spring-boot-actuator-2.0.3.RELEASE.jar:2.0.3.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:320) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:127) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:91) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:119) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:137) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:170) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.authentication.www.BasicAuthenticationFilter.doFilterInternal(BasicAuthenticationFilter.java:158) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at cloud.test.server.filters.JwtAuthenticationTokenFilter.doFilterInternal(JwtAuthenticationTokenFilter.java:141) [classes/:?]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at cloud.test.server.filters.TenantFilter.doFilterInternal(TenantFilter.java:30) [classes/:?]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:116) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:66) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:105) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:215) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:178) [spring-security-web-5.0.6.RELEASE.jar:5.0.6.RELEASE]
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:357) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:270) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:109) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:496) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1468) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_181]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_181]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.31.jar:8.5.31]
    at java.lang.Thread.run(Thread.java:748) [?:1.8.0_181]
Caused by: com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: org.springframework.hateoas.PagedResources["_embedded"])
    at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:391) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:351) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ser.std.StdSerializer.wrapAndThrow(StdSerializer.java:316) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:727) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:319) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ObjectWriter$Prefetch.serialize(ObjectWriter.java:1396) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:913) ~[jackson-databind-2.9.6.jar:2.9.6]
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:286) ~[spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    ... 113 more
Caused by: java.lang.NullPointerException
    at org.springframework.data.rest.core.support.RepositoryRelProvider.getCollectionResourceRelFor(RepositoryRelProvider.java:52) ~[spring-data-rest-core-3.0.8.RELEASE.jar:3.0.8.RELEASE]
    at org.springframework.hateoas.core.DelegatingRelProvider.getCollectionResourceRelFor(DelegatingRelProvider.java:50) ~[spring-hateoas-0.24.0.RELEASE.jar:?]
    at org.springframework.hateoas.hal.HalEmbeddedBuilder.getDefaultedRelFor(HalEmbeddedBuilder.java:125) ~[spring-hateoas-0.24.0.RELEASE.jar:?]
    at org.springframework.hateoas.hal.HalEmbeddedBuilder.add(HalEmbeddedBuilder.java:78) ~[spring-hateoas-0.24.0.RELEASE.jar:?]
    at org.springframework.hateoas.hal.Jackson2HalModule$EmbeddedMapper.map(Jackson2HalModule.java:904) ~[spring-hateoas-0.24.0.RELEASE.jar:?]
    at org.springframework.hateoas.hal.Jackson2HalModule$HalResourcesSerializer.serialize(Jackson2HalModule.java:338) ~[spring-hateoas-0.24.0.RELEASE.jar:?]
    at org.springframework.hateoas.hal.Jackson2HalModule$HalResourcesSerializer.serialize(Jackson2HalModule.java:308) ~[spring-hateoas-0.24.0.RELEASE.jar:?]
    at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:319) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ObjectWriter$Prefetch.serialize(ObjectWriter.java:1396) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:913) ~[jackson-databind-2.9.6.jar:2.9.6]
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:286) ~[spring-web-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    ... 113 more
14/12/2018 09:51:58,572 DEBUG http-nio-8082-exec-5 ApplicationExceptionHandler:263 -

总结一下，如果我调用/frames/{property}/groupBy端点甚至一切正常，但如果我仅调用端点autocomplete一次，然后再次调用/frames/{property}/groupBy端点，我马上就会遇到异常

这很奇怪，即使我在代码中进行调试，也不清楚什么地方出了问题。你有什么提示吗？可能是Spring / Jackson中的错误吗？

###################### UPDATE ##################### ####

真的在内部调试，最后我找到了引发异常的行。

这是org.springframework.data.rest.core.support.RepositoryRelProvider中的这段代码：

@Override
    public String getCollectionResourceRelFor(Class<?> type) {
        return mappings.getObject().getMetadataFor(type).getRel();
    }

实际上我的类型为String，而mappings.getObject().getMetadataFor(type)为null，因此当它尝试调用getRel()时会引发异常。

这是一个错误吗？

####################### UPDATE 2 #################### #####

我发现问题出在我使用公开存储库的方法时：

@Transactional
@PreAuthorize("isAuthenticated()")
public interface ContactRepository extends JpaRepository<Contact, Long> {

 @Query(value = "SELECT c FROM Contact c WHERE :searchString IS NULL OR (companyName LIKE CONCAT(:searchString,'%')) OR (CONCAT(lastName,' ',firstName) LIKE CONCAT(:searchString,'%'))")
    public Page<Contact> autocomplete(@Param("searchString") String searchString, Pageable pageable);

}

实际上，在这种情况下，在RepositorySearchController.executeQueryMethod()中它检测到参数是一个字符串，并调用ResourceMetadata metadata = mappings.getMetadataFor(domainType.getType());，在PersistentEntitiesResourceMappings中将空值放入ResourceMetadata的缓存中。 / p>

不确定这是否是仅由于配置错误所致，但是如果我将端点移动到调用该存储库的控制器中，那么一切都很好。

Answer 1

Jackson尝试从其getter序列化一个字段。由于某种原因，getter方法可能会引发NullPointerException。

如果要让Jackson忽略此字段，则可以使用@JsonIgnore注释getter或使用@JsonIgnoreProperties注释类并指定属性名称。

Spring HttpMessageNotWritableException无法编写JSON，NullPointerException

1 个答案: