No @XmlRootElement generated by JAXB

Question

I'm trying to generate Java classes from the FpML (Finanial Products Markup Language) version 4.5. A ton of code is generated, but I cannot use it. Trying to serialize a simple document I get this:

javax.xml.bind.MarshalException
  - with linked exception: [com.sun.istack.SAXException2: unable
  to marshal type
  "org.fpml._2008.fpml_4_5.PositionReport"
  as an element because it is missing an
  @XmlRootElement annotation]

In fact no classses have the @XmlRootElement annotation, so what can I be doing wrong?. I'm pointing xjc (JAXB 2.1) to fpml-main-4-5.xsd, which then includes all types.

Solution 1

To tie together what others have already stated or hinted at, the rules by which JAXB XJC decides whether or not to put the @XmlRootElement annotation on a generated class are non trivial (see this article).

@XmlRootElement exists because the JAXB runtime requires certain information in order to marshal/unmarshal a given object, specifically the XML element name and namespace. You can't just pass any old object to the Marshaller. @XmlRootElement provides this information.

The annotation is just a convenience, however - JAXB does not require it. The alternative to is to use JAXBElement wrapper objects, which provide the same information as @XmlRootElement, but in the form of an object, rather than an annotation.

However, JAXBElement objects are awkward to construct, since you need to know the XML element name and namespace, which business logic usually doesn't.

Thankfully, when XJC generates a class model, it also generates a class called ObjectFactory. This is partly there for backwards compatibility with JAXB v1, but it's also there as a place for XJC to put generated factory methods which create JAXBElement wrappers around your own objects. It handles the XML name and namespace for you, so you don't need to worry about it. You just need to look through the ObjectFactory methods (and for large schema, there can be hundreds of them) to find the one you need.

Solution 2

This is mentioned at the bottom of the blog post already linked above but this works like a treat for me:

Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);
marshaller.marshal(new JAXBElement<MyClass>(new QName("uri","local"), MyClass.class, myClassInstance), System.out);

Solution 3

As hinted at in one of the above answers, you won't get an XMLRootElement on your root element if in the XSD its type is defined as a named type, since that named type could be used elsewhere in your XSD. Try mking it an anonymous type, i.e. instead of:

<xsd:element name="myRootElement" type="MyRootElementType" />

<xsd:complexType name="MyRootElementType">
...
</xsd:complexType>

you would have:

<xsd:element name="myRootElement">
    <xsd:complexType>
    ...
    <xsd:complexType>
</xsd:element>

Solution 4

@XmlRootElement is not needed for unmarshalling - if one uses the 2 parameter form of Unmarshaller#unmarshall.

So, if instead of doing:

UserType user = (UserType) unmarshaller.unmarshal(new StringReader(responseString));

one should do:

JAXBElement<UserType> userElement = unmarshaller.unmarshal(someSource, UserType.class);
UserType user = userElement.getValue();

The latter code will not require @XmlRootElement annotation at UserType class level.

Solution 5

You can fix this issue using the binding from How to generate @XmlRootElement Classes for Base Types in XSD?.

Here is an example with Maven

        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>jaxb2-maven-plugin</artifactId>
            <version>1.3.1</version>
            <executions>
                <execution>
                    <id>xjc</id>
                    <goals>
                        <goal>xjc</goal>
                    </goals>
                </execution>
            </executions>
            <configuration>
                <schemaDirectory>src/main/resources/xsd</schemaDirectory>
                <packageName>com.mycompany.schemas</packageName>
                <bindingFiles>bindings.xjb</bindingFiles>
                <extension>true</extension>
            </configuration>
        </plugin>

Here is the binding.xjb file content

<?xml version="1.0"?>
<jxb:bindings version="1.0" xmlns:jxb="http://java.sun.com/xml/ns/jaxb"
              xmlns:xjc= "http://java.sun.com/xml/ns/jaxb/xjc"
              jxb:extensionBindingPrefixes="xjc" xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <jxb:bindings schemaLocation="path/to/myschema.xsd" node="/xs:schema">
        <jxb:globalBindings>
            <xjc:simple/>
        </jxb:globalBindings>
    </jxb:bindings>
</jxb:bindings>

View more solutions

Comments

[Joe Bane]

This worked well for me, thank you. I also found that I was marshaling the wrong JAXB object (not the root like I thought) in the process of going through this. I forgot to create a JAXBElement and was trying to marshal just the returned object from the ObjectFactory class I had obtained from binding. This basically took care of the issue altogether (in case anyone else runs up against the same problem).

[Chris]

Do you know of an equally elegant way to marshal an object that doesn't have XmlRootElement - without wrapping it in a JAXBElement as mentioned by skaffman, Gurnard et al?

[Marcin Górecki]

Great link to the article in first paragraph.

[Arthur]

Special case solution: when you can modify the xsd used for class generation: After reading the link provided in this answer the solution in my case was to modify the xsd file used to generate the classes: I changed the definition of the root element to an inlined definition instead of using the reference to a type defined separetely. These allows JAXB to set this element as @XmlRootElement, which was not possible with the elementType which was used before for the root element.

[Pawel Veselov]

<scowl> changing root element to be of inline type, however, makes all classes to be inner classes of the root type. Also, even if the root element type is defined AFTER the root element itself (apparently allowed by schema), JAXB will still not annotate with @XmlRootElement.

[bdoughan]

@PawelVeselov - The following will help you generate top level classes: blog.bdoughan.com/2011/07/jaxb-xjc-and-nested-classes.html

[MrSmith42]

This example helped me to generate the XmlRootElementannotations I needed Configure Maven to generate classes from XML Schema using JAXB

[supernova]

+1 Works perfectly! One edit for more clarity... In your solution 'someSource' is very vague term. To elaborate : JAXBElement<TargetClazz> root = unmarshaller.unmarshal(new StreamSource(new File("some.xml")),TargetClazz.class);

[vikingsteve]

i.e. new ObjectFactory().createPositionReport(positionReport) returns JAXBElement<PositionReport>

[Pedro Dusso]

I prefer the marked answer, but this works for me too.

[dvtoever]

Indeed, using <xjc:simple> in the binding.xjb file did the trick. Awesome solution if you don't want to change your marshaling code or your WSDL. Note that xjc:simple generates different method names (plural) for collection getters (getOrders instead of getOrder for example)

[Carl G]

What if the generated ObjectFactory method does not create a method that wraps the argument in a JXBElement? In my case, the factory method is 0-arity and just returns a new object. (Why are some classes given JAXBElement wrapper helpers and others not?) I guess in that case we must create the wrapper ourselves?

[NullPumpkinException]

This worked for me with JDK 1.7u71. A top level element gets assigned the @XmlRootElement by xjc. Initially I had a top level complex type only. Having to wrap in a JAXBElement is plain ugly.

[Evan LaHurd]

I've noticed this sometimes too @CarlG. Can anyone explain?

[manash]

@CarlG I'm in the same situation - no XmlRootElement nor JAXBElement appears in my classes. Have you found a solution for this case?

[manash]

That's not true for me. My type is anonymous (embedded inside my root element) and no XmlRootElement annotation is generated. Any idea?

[manash]

I have a case where my ObjectFactory class only defines methods that return regular instances and not JAXBElement instances...

[Arun]

what is jc in the above snippet?

[Gurnard]

@ArunRaj it is the JAXBContext class

[Steve Pitchers]

Further elaboration of 'someSource':String pathname = "file.xml"; InputStream stream = new FileInputStream(pathname); JAXBContext jaxbContext = JAXBContext.newInstance(UserType.class); Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller(); XMLInputFactory factory = XMLInputFactory.newInstance(); XMLEventReader someSource = factory.createXMLEventReader(stream); JAXBElement<UserType> userElement = jaxbUnmarshaller.unmarshal(someSource, UserType.class); UserType user = userElement.getValue();

[aliopi]

the wrapping tag should be <jaxb:bindings> ... <jaxws:bindings> ... </jaxws:bindings> ... </jaxb:bindings>

[Tristan]

404 : "We're sorry the java.net site has closed. Most Open Source projects previously hosted on java.net have been relocated."

[D-Klotz]

web.archive.org/web/20070812073809/http://weblogs.java.net/b‌​log/…

[MattWeiler]

Using the ObjectFactory helped to solve my problem, thanks :)

[Angelina]

to your point... how do I use JAXBElement<?> create...() methods from ObjectFactory for nested elements? i.e. : <SOAP-ENV:Header> <wsse:Security> <wsse:UsernameToken></wsse:UsernameToken> </wsse:Security> </SOAP-ENV:Header> I get: "unable to marshal type "UsernameTokenType" as an element because it is missing an @XmlRootElement annotation"

[RRR_J]

Thanks for giving the code reference with spring webservice template as was struggling to figure it out for quite some time!

[Boris Mitioglov]

this also helps in case you see your ObjectFactory generated methods without parameters

[gratinierer]

indeed this pretty clear code expample did the trick for me. Thanks for saving me from deep-diving into library-code :)

[Simon Logic]

how to dynamically extract namespace from package-info?