JAXB编组在webservice调用中失败

Question

我有一个Web服务，在调用时抛出异常。它失败了编组我的实体。任何人都可以看到我做错了什么。 （为了便于阅读，我省略了很多代码）

我的实体

@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;
    }   
}

网络服务

@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());
}

异常

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

您的Question班级有List Answer。由于Answer是一个抽象类，因此需要在相应的值上使用类型指示符，如下所示，以避免异常。

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