CXF Error Unmarshalling Error UnsupportedOperationException

Question

TL;DR For some reason I can't unmarshall a fairly simple object in a Java-first web service using CXF.

I have a Java-First CXF Web Service with an API similar to:

@WebMethod
public SearchResponse search(@WebParam(name = "searchRequest") SearchRequest searchRequest);    

The response (the class that won't unmarshall) is roughly:

public class SearchResponse {

    private List<SearchResult> results;
    public List<SearchResult> getResults() {
        return results;
    }
    public void setResults(List<SearchResult> results) {
        this.results = results;
    }
}

SearchResult is a dead-simple two property class:

public class SearchResult {
    private long id;
    private String name;

    public long getId() {
        return id;
    }
    public void setId(long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

I can call this service through Soap-UI and it works perfectly. However, when I call using a jaxws client I get an error:

javax.xml.ws.soap.SOAPFaultException: Unmarshalling Error: null 
    at org.apache.cxf.jaxws.JaxWsClientProxy.invoke(JaxWsClientProxy.java:143)
    at $Proxy67.search(Unknown Source)
    at com.blah.MyTest.curseYouSearch(MyTest.java:76)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:59)
    at org.junit.internal.runners.MethodRoadie.runTestMethod(MethodRoadie.java:98)
    at org.junit.internal.runners.MethodRoadie$2.run(MethodRoadie.java:79)
    at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:87)
    at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:77)
    at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:42)
    at org.junit.internal.runners.JUnit4ClassRunner.invokeTestMethod(JUnit4ClassRunner.java:88)
    at org.junit.internal.runners.JUnit4ClassRunner.runMethods(JUnit4ClassRunner.java:51)
    at org.junit.internal.runners.JUnit4ClassRunner$1.run(JUnit4ClassRunner.java:44)
    at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:27)
    at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:37)
    at org.junit.internal.runners.JUnit4ClassRunner.run(JUnit4ClassRunner.java:42)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
Caused by: java.lang.UnsupportedOperationException
    at java.util.AbstractList.add(AbstractList.java:131)
    at java.util.AbstractList.add(AbstractList.java:91)
    at com.sun.xml.internal.bind.v2.runtime.reflect.Lister$CollectionLister.addToPack(Lister.java:290)
    at com.sun.xml.internal.bind.v2.runtime.reflect.Lister$CollectionLister.addToPack(Lister.java:254)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.Scope.add(Scope.java:106)
    at com.sun.xml.internal.bind.v2.runtime.property.ArrayERProperty$ReceiverImpl.receive(ArrayERProperty.java:195)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallingContext.endElement(UnmarshallingContext.java:524)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.StAXStreamConnector.handleEndElement(StAXStreamConnector.java:206)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.StAXStreamConnector.bridge(StAXStreamConnector.java:170)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal0(UnmarshallerImpl.java:351)
    at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal(UnmarshallerImpl.java:330)
    at org.apache.cxf.jaxb.JAXBEncoderDecoder.unmarshall(JAXBEncoderDecoder.java:610)
    at org.apache.cxf.jaxb.JAXBEncoderDecoder.unmarshall(JAXBEncoderDecoder.java:530)
    at org.apache.cxf.jaxb.io.DataReaderImpl.read(DataReaderImpl.java:114)
    at org.apache.cxf.interceptor.DocLiteralInInterceptor.handleMessage(DocLiteralInInterceptor.java:99)
    at org.apache.cxf.phase.PhaseInterceptorChain.doIntercept(PhaseInterceptorChain.java:236)
    at org.apache.cxf.endpoint.ClientImpl.onMessage(ClientImpl.java:658)
    at org.apache.cxf.transport.http.HTTPConduit$WrappedOutputStream.handleResponseInternal(HTTPConduit.java:2139)
    at org.apache.cxf.transport.http.HTTPConduit$WrappedOutputStream.handleResponse(HTTPConduit.java:2022)
    at org.apache.cxf.transport.http.HTTPConduit$WrappedOutputStream.close(HTTPConduit.java:1947)
    at org.apache.cxf.transport.AbstractConduit.close(AbstractConduit.java:66)
    at org.apache.cxf.transport.http.HTTPConduit.close(HTTPConduit.java:632)
    at org.apache.cxf.interceptor.MessageSenderInterceptor$MessageSenderEndingInterceptor.handleMessage(MessageSenderInterceptor.java:62)
    at org.apache.cxf.phase.PhaseInterceptorChain.doIntercept(PhaseInterceptorChain.java:236)
    at org.apache.cxf.endpoint.ClientImpl.invoke(ClientImpl.java:472)
    at org.apache.cxf.endpoint.ClientImpl.invoke(ClientImpl.java:302)
    at org.apache.cxf.endpoint.ClientImpl.invoke(ClientImpl.java:254)
    at org.apache.cxf.frontend.ClientProxy.invokeSync(ClientProxy.java:73)
    at org.apache.cxf.jaxws.JaxWsClientProxy.invoke(JaxWsClientProxy.java:123)
    ... 24 more

I can set a breakpoint on AbstractList.add and based on the resulting stack it appears unmarshalling is attempting to add to the empty list, which of course is immutable:

Thread [main] (Suspended (breakpoint at line 131 in AbstractList))  
    Collections$EmptyList(AbstractList<E>).add(int, E) line: 131    
    Collections$EmptyList(AbstractList<E>).add(E) line: 91  
    Lister$CollectionLister<BeanT,T>.addToPack(T, Object) line: 290 
    Lister$CollectionLister<BeanT,T>.addToPack(Object, Object) line: 254    
    Scope<BeanT,PropT,ItemT,PackT>.add(Accessor<BeanT,PropT>, Lister<BeanT,PropT,ItemT,PackT>, ItemT) line: 106 
    ArrayERProperty$ReceiverImpl.receive(UnmarshallingContext$State, Object) line: 195  
    UnmarshallingContext.endElement(TagName) line: 524  
    StAXStreamConnector.handleEndElement() line: 206    
    StAXStreamConnector.bridge() line: 170  
    UnmarshallerImpl.unmarshal0(XMLStreamReader, JaxBeanInfo) line: 351 
    UnmarshallerImpl.unmarshal(XMLStreamReader, Class<T>) line: 330 
    JAXBEncoderDecoder.unmarshall(Unmarshaller, Object, QName, Class<?>, boolean) line: 610 
    JAXBEncoderDecoder.unmarshall(Unmarshaller, Object, MessagePartInfo, boolean) line: 530 
    DataReaderImpl<T>.read(MessagePartInfo, T) line: 114    
    DocLiteralInInterceptor.handleMessage(Message) line: 99 
    PhaseInterceptorChain.doIntercept(Message) line: 236    
    ClientImpl.onMessage(Message) line: 658 
    HTTPConduit$WrappedOutputStream.handleResponseInternal() line: 2139 
    HTTPConduit$WrappedOutputStream.handleResponse() line: 2022 
    HTTPConduit$WrappedOutputStream.close() line: 1947  
    HTTPConduit(AbstractConduit).close(Message) line: 66    
    HTTPConduit.close(Message) line: 632    
    MessageSenderInterceptor$MessageSenderEndingInterceptor.handleMessage(Message) line: 62 
    PhaseInterceptorChain.doIntercept(Message) line: 236    
    ClientImpl.invoke(BindingOperationInfo, Object[], Map<String,Object>, Exchange) line: 472   
    ClientImpl.invoke(BindingOperationInfo, Object[], Exchange) line: 302   
    ClientImpl.invoke(BindingOperationInfo, Object...) line: 254    
    JaxWsClientProxy(ClientProxy).invokeSync(Method, BindingOperationInfo, Object[]) line: 73   
    JaxWsClientProxy.invoke(Object, Method, Object[]) line: 123 
    ...endless stack lines omitted...

My client is setup in Spring as a jaxws:client:

<jaxws:client id="searchServiceClient"
    serviceClass="qualified.class.of.Service"
    address="${url.searchService}">
</jaxws:client>   

We have numerous other web services that return List in a very similar fashion and work fine; I am somewhat at a loss as to what the difference is with this one.

The system is using Java 6, CXF 2.2.3.

Any suggestions would be most welcome.

Answer 1

I think I suffered the same issue and have a solution at least in my case and it may help yours.

Use-case here was slightly different than yours in that I was reading an XML file from a flat application. No web interactions.

The configuration file's significant elements were:

private static final List<StrategyConfiguration<Transaction>> EMPTY_CONFIGURATION_LIST = Collections.emptyList();
private List<StrategyConfiguration<Transaction>> configurations;
@XmlElementWrapper(name = "boundaries")
@XmlElements({
    @XmlElement(name = "a", type = abtStrategyConfig.class),
    @XmlElement(name = "b", type = bbtStrategyConfig.class),
    @XmlElement(name = "c", type = cbtStrategyConfig.class)
})
public void setConfigurations(List<StrategyConfiguration<Transaction>> configurations) {
    this.configurations = configurations;
}
public List<StrategyConfiguration<Transaction>> getConfigurations() {
    if (configurations == null) {
        return EMPTY_CONFIGURATION_LIST;
    }
    return configurations;
}

I have not had time to investigate the "why" but a debug run showed the "what" that was causing the issue. The null-safe "get" accessor was being called prior to the setter. I imagine this was to provide a type safety check. The "empty" list was being returned, non-null, and was then used as the basis for the subsequent set.

I found that by providing a straight setter & getter, and then provide a null-safe getter for outside use I cleared up the error.

private static final List<StrategyConfiguration<Transaction>> EMPTY_CONFIGURATION_LIST = Collections.emptyList();
private List<StrategyConfiguration<Transaction>> configurations;
@XmlElementWrapper(name = "boundaries")
@XmlElements({
    @XmlElement(name = "a", type = abtStrategyConfig.class),
    @XmlElement(name = "b", type = bbtStrategyConfig.class),
    @XmlElement(name = "c", type = cbtStrategyConfig.class)
})
public void setJaxBConfigurations(List<StrategyConfiguration<Transaction>> configurations) {
    this.configurations = configurations;
}
public List<StrategyConfiguration<Transaction>> getJaxBConfigurations() {
    return configurations;
}
public List<StrategyConfiguration<Transaction>> getConfigurations() {
    List<StrategyConfiguration<Transaction>> response = getConfigurationConfigs();
    if (response == null) {
        response = EMPTY_CONFIGURATION_LIST;
    }
    return response;
}