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POInstantiationException during JAXB Unmarshalling (abstract base class, with @XmlSeeAlso concrete sub class)
 

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    <p>I am running into JAXB Unmarshalling error as below. The foo.bar.Base is an abstract class, with an @XmlSeeAlso annotation, which lists foo.bar.SubBase (which is a concrete subclass of foo.bar.Base)</p> <p>Both of the above classes are statically reachable from a main/entry class: com.example.Request</p> <p>The JAXBContext is create using the packages string variant viz:</p> <pre><code>JAXBContext.newInstance("com.example",...); </code></pre> <p>The above created JAXBContext correctly lists all the three classes : <code>com.example.Request, foo.bar.Base and foo.bar.SubBase as "classes known to this JAXBContext"</code></p> <p>But it fails at runtime during the unmarshal call below.. I am unable to figure out what is wrong here. </p> <pre><code>unmarshaller.unmarshal(&lt;some-DOM-Element-Instance&gt;, com.example.Request.class); </code></pre> <p>Any pointers will be appreciated! Thanks!</p> <p>The stacktrace is:</p> <pre><code> Caused by: javax.xml.bind.UnmarshalException: Unable to create an instance of foo.bar.Base - with linked exception: [java.lang.InstantiationException] at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallingContext.handleEvent(UnmarshallingContext.java:642) at com.sun.xml.bind.v2.runtime.unmarshaller.Loader.reportError(Loader.java:254) at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallingContext.createInstance(UnmarshallingContext.java:609) at com.sun.xml.bind.v2.runtime.unmarshaller.StructureLoader.startElement(StructureLoader.java:181) at com.sun.xml.bind.v2.runtime.unmarshaller.XsiTypeLoader.startElement(XsiTypeLoader.java:76) at com.sun.xml.bind.v2.runtime.unmarshaller.ProxyLoader.startElement(ProxyLoader.java:55) at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallingContext._startElement(UnmarshallingContext.java:481) at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallingContext.startElement(UnmarshallingContext.java:459) at com.sun.xml.bind.v2.runtime.unmarshaller.InterningXmlVisitor.startElement(InterningXmlVisitor.java:71) at com.sun.xml.bind.v2.runtime.unmarshaller.SAXConnector.startElement(SAXConnector.java:148) at com.sun.xml.bind.unmarshaller.DOMScanner.visit(DOMScanner.java:239) at com.sun.xml.bind.unmarshaller.DOMScanner.visit(DOMScanner.java:276) at com.sun.xml.bind.unmarshaller.DOMScanner.visit(DOMScanner.java:245) at com.sun.xml.bind.unmarshaller.DOMScanner.scan(DOMScanner.java:122) at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal0(UnmarshallerImpl.java:314) at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal(UnmarshallerImpl.java:293) Caused by: java.lang.InstantiationException at sun.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:30) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at com.sun.xml.bind.v2.ClassFactory.create0(ClassFactory.java:123) at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.createInstance(ClassBeanInfoImpl.java:261) at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallingContext.createInstance(UnmarshallingContext.java:603) ... 69 more </code></pre> <p>EDIT @Blaise and @Ross</p> <p>Thank you very much Blaise and Ross for your pointers. I think I should have included the schema that is being worked off, here. The relevant schema looks like this:</p> <pre><code> &lt;xs:complexType name="Request"&gt; &lt;xs:sequence&gt; &lt;xs:element name="selectedBase" form="unqualified" nillable="true" type="xs:anyType" minOccurs="0"/&gt; &lt;xs:element name="selectedSubBase" form="unqualified" nillable="true" type="ns1:SubBase" minOccurs="0"/&gt; &lt;/xs:sequence&gt; &lt;/xs:complexType&gt; &lt;xs:complexType name="Base"&gt; &lt;xs:sequence&gt; &lt;xs:element name="ID" form="unqualified" nillable="true" type="xs:string" minOccurs="0"/&gt; &lt;/xs:sequence&gt; &lt;/xs:complexType&gt; &lt;xs:complexType name="SubBase"&gt; &lt;xs:complexContent&gt; &lt;xs:extension base="ns1:Base"&gt; &lt;xs:sequence&gt; &lt;xs:element name="subBaseElement" form="unqualified" nillable="true" type="xs:anyType" minOccurs="0"/&gt; &lt;/xs:sequence&gt; &lt;/xs:extension&gt; &lt;/xs:complexContent&gt; &lt;/xs:complexType&gt; </code></pre> <p>So the schema doesn't have substitution group definition (so I guess <code>@XmlElementRef</code> doesn't apply here, or would it still work?), but is using extension. The payload will be :</p> <pre><code>&lt;ns:Request&gt; &lt;selectedBase&gt;123&lt;/selectedBase&gt; &lt;selectedSubBase&gt; &lt;ID&gt;321&lt;/ID&gt; &lt;subBaseElement&gt;123&lt;/subBaseElement&gt; &lt;/selectedSubBase&gt; &lt;/ns:Request&gt; </code></pre> <p>So , the element in the payload occuring is <code>&lt;selectedSubBase&gt;</code> and not <code>&lt;selectedBase xsi:type="ns:SubBase"/&gt;</code></p> <p>So which strategy would apply here?</p>
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