JAXB marshalling терпит неудачу в вызове webservice

Question

У меня есть веб-служба, которая генерирует исключение при вызове. Он терпит неудачу с сортировкой моей сущности. Может ли кто-нибудь увидеть, что я делаю неправильно. (Я опустил много кода для удобства чтения)

Мои объекты

@Entity 
@Table(name="Question", schema="exam") 
@XmlRootElement 
@XmlAccessorType(XmlAccessType.PROPERTY) 
public class Question extends BaseEntity { 

    private static final long serialVersionUID = 1L; 

    @ManyToMany 
    @JoinTable(name="Questions_Answers", schema="relation", 
      joinColumns=@JoinColumn(name="questionId", referencedColumnName="id"), 
      inverseJoinColumns=@JoinColumn(name="answerId", referencedColumnName="id")) 
    private List<Answer> answers = new ArrayList<Answer>(); 



    public List<Answer> getAnswers(){ 
     return this.answers; 
    } 

    public void setAnswers(List<Answer> answers){ 
     this.answers = answers; 
    } 


} 


@Entity 
@Table(name="Answer", schema="exam") 
@Inheritance(strategy=InheritanceType.JOINED) 
@DiscriminatorColumn(name="AnswerType", discriminatorType=DiscriminatorType.STRING) 
@XmlRootElement 
@XmlAccessorType(XmlAccessType.PROPERTY) 
@XmlSeeAlso({MultipleAnswer.class}) 
public abstract class Answer extends BaseEntity { 

    private static final long serialVersionUID = 1L;  

    @ManyToMany(mappedBy="answers") 
    private List<Question> questions = new ArrayList<Question>(); 


    @XmlTransient 
    public List<Question> getQuestions() { 
     return questions; 
    } 

    public void setQuestions(List<Question> questions) { 
     this.questions = questions; 
    } 
} 

@Entity 
@Table(name="MultipleAnswer", schema="exam") 
@DiscriminatorValue(value="MULTIPLE_CHOICE") 
@XmlRootElement 
@XmlAccessorType(XmlAccessType.PROPERTY) 
public class MultipleAnswer extends Answer { 

    private static final long serialVersionUID = 1L; 

    public MultipleAnswer(){ 

    } 

    @Column(name="answer") 
    private String answer; 

    @Column(name="answerExplanation") 
    private String answerExplanation; 

    @Column(name="isCorrect") 
    private boolean isCorrect; 

    public String getAnswer() { 
     return answer; 
    } 

    public void setAnswer(String answer) { 
     this.answer = answer; 
    } 

    public String getAnswerExplanation() { 
     return answerExplanation; 
    } 

    public void setAnswerExplanation(String answerExplanation) { 
     this.answerExplanation = answerExplanation; 
    } 

    public boolean isCorrect() { 
     return isCorrect; 
    } 

    public void setCorrect(boolean isCorrect) { 
     this.isCorrect = isCorrect; 
    } 
} 

Веб-сервис

@POST 
@Path("/save") 
@Consumes({MediaType.APPLICATION_JSON}) 
public void saveQuestion(Question question) { 
    log.warning("Title: " + question.getTitle()); 
    log.warning("Number of answers: " + question.getAnswers().size()); 
} 

Исключение

Exception [EclipseLink-44] (Eclipse Persistence Services - 2.5.0.v20130507-3faac2b): org.eclipse.persistence.exceptions.DescriptorException 
Exception Description: Missing class indicator field from database row [UnmarshalRecordImpl()]. 
Descriptor: XMLDescriptor(se.questify.entities.exam.Answer --> [DatabaseTable(answer)]) 
    at org.eclipse.persistence.exceptions.DescriptorException.missingClassIndicatorField(DescriptorException.java:957) 
    at org.eclipse.persistence.internal.oxm.XMLRelationshipMappingNodeValue.processChild(XMLRelationshipMappingNodeValue.java:83) 
    at org.eclipse.persistence.internal.oxm.XMLCompositeCollectionMappingNodeValue.startElement(XMLCompositeCollectionMappingNodeValue.java:184) 
    at org.eclipse.persistence.internal.oxm.record.UnmarshalRecordImpl.startElement(UnmarshalRecordImpl.java:834) 
    at org.eclipse.persistence.internal.oxm.record.json.JSONReader.parse(JSONReader.java:421) 
    at org.eclipse.persistence.internal.oxm.record.json.JSONReader.parse(JSONReader.java:241) 
    at org.eclipse.persistence.internal.oxm.record.json.JSONReader.parseRoot(JSONReader.java:179) 
    at org.eclipse.persistence.internal.oxm.record.json.JSONReader.parse(JSONReader.java:125) 
    at org.eclipse.persistence.internal.oxm.record.SAXUnmarshaller.unmarshal(SAXUnmarshaller.java:972) 
    at org.eclipse.persistence.internal.oxm.record.SAXUnmarshaller.unmarshal(SAXUnmarshaller.java:425) 
    at org.eclipse.persistence.internal.oxm.record.SAXUnmarshaller.unmarshal(SAXUnmarshaller.java:375) 
    at org.eclipse.persistence.internal.oxm.record.SAXUnmarshaller.unmarshal(SAXUnmarshaller.java:705) 
    at org.eclipse.persistence.oxm.XMLUnmarshaller.unmarshal(XMLUnmarshaller.java:655) 
    at org.eclipse.persistence.jaxb.JAXBUnmarshaller.unmarshal(JAXBUnmarshaller.java:301) 
    at org.eclipse.persistence.jaxb.rs.MOXyJsonProvider.readFrom(MOXyJsonProvider.java:580) 
    at org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$TerminalReaderInterceptor.aroundReadFrom(ReaderInterceptorExecutor.java:181) 
    at org.glassfish.jersey.message.internal.ReaderInterceptorExecutor.proceed(ReaderInterceptorExecutor.java:134) 
    at org.glassfish.jersey.server.internal.MappableExceptionWrapperInterceptor.aroundReadFrom(MappableExceptionWrapperInterceptor.java:72) 
    at org.glassfish.jersey.message.internal.ReaderInterceptorExecutor.proceed(ReaderInterceptorExecutor.java:134) 
    at org.glassfish.jersey.message.internal.MessageBodyFactory.readFrom(MessageBodyFactory.java:988) 
    at org.glassfish.jersey.message.internal.InboundMessageContext.readEntity(InboundMessageContext.java:833) 
    at org.glassfish.jersey.server.ContainerRequest.readEntity(ContainerRequest.java:245) 
    at org.glassfish.jersey.server.internal.inject.EntityParamValueFactoryProvider$EntityValueFactory.get(EntityParamValueFactoryProvider.java:96) 
    at org.glassfish.jersey.server.internal.inject.AbstractHttpContextValueFactory.provide(AbstractHttpContextValueFactory.java:66) 
    at org.glassfish.jersey.server.spi.internal.ParameterValueHelper.getParameterValues(ParameterValueHelper.java:81) 
    at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$AbstractMethodParamInvoker.getParamValues(JavaResourceMethodDispatcherProvider.java:121) 
    at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$VoidOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:136) 
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:91) 
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:346) 
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:341) 
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:101) 
    at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:224) 
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:271) 
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:267) 
    at org.glassfish.jersey.internal.Errors.process(Errors.java:315) 
    at org.glassfish.jersey.internal.Errors.process(Errors.java:297) 
    at org.glassfish.jersey.internal.Errors.process(Errors.java:267) 
    at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:317) 
    at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:198) 
    at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:946) 
    at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:323) 
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:372) 
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:335) 
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:218) 
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682) 
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318) 
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160) 
    at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734) 
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673) 
    at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99) 
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174) 
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:357) 
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:260) 
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188) 
    at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191) 
    at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168) 
    at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189) 
    at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119) 
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288) 
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:206) 
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136) 
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114) 
    at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77) 
    at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838) 
    at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:113) 
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115) 
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55) 
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135) 
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564) 
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544) 
    at java.lang.Thread.run(Thread.java:722) 

Answer 1

Ваш Question класс имеет List от Answer. Поскольку Answer - абстрактный класс, для исключения исключения вам понадобится индикатор типа для соответствующих значений, подобных приведенным ниже.

{ 
    "answers" : [ { 
     "type" : "multipleAnswer", 
     "correct" : false 
    }, { 
     "type" : "multipleAnswer", 
     "correct" : true 
    } ] 
}