Serialization of a polymorphic class As.Property with Identity information doesn't work

[pgelinas]

Basically, XmlBeanSerializer#serializeWithType doesn't take into account Object Id when it sets "NextIsAttribute". I'll try to attach a unit test, probably tomorrow.

Exception in thread "main" java.io.IOException: javax.xml.stream.XMLStreamException: Trying to write an attribute when there is no open start element.
    at com.fasterxml.jackson.dataformat.xml.util.StaxUtil.throwXmlAsIOException(StaxUtil.java:24)
    at com.fasterxml.jackson.dataformat.xml.ser.ToXmlGenerator.writeString(ToXmlGenerator.java:498)
    at com.fasterxml.jackson.databind.ser.std.StringSerializer.serialize(StringSerializer.java:39)
    at com.fasterxml.jackson.databind.ser.std.StringSerializer.serialize(StringSerializer.java:21)
    at com.fasterxml.jackson.databind.ser.impl.WritableObjectId.writeAsId(WritableObjectId.java:36)
    at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase._serializeWithObjectId(BeanSerializerBase.java:575)
    at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeWithType(BeanSerializerBase.java:514)
    at com.fasterxml.jackson.dataformat.xml.ser.XmlBeanSerializer.serializeWithType(XmlBeanSerializer.java:253)
    at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:543)
    at com.fasterxml.jackson.dataformat.xml.ser.XmlBeanSerializer.serializeFields(XmlBeanSerializer.java:161)
    at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase._serializeWithObjectId(BeanSerializerBase.java:560)
    at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:145)
    at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:100)
    at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:21)
    at com.fasterxml.jackson.databind.ser.std.AsArraySerializerBase.serialize(AsArraySerializerBase.java:183)
    at com.fasterxml.jackson.dataformat.xml.ser.XmlBeanPropertyWriter.serializeAsField(XmlBeanPropertyWriter.java:127)
    at com.fasterxml.jackson.dataformat.xml.ser.XmlBeanSerializer.serializeFields(XmlBeanSerializer.java:161)
    at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:152)
    at com.fasterxml.jackson.dataformat.xml.ser.XmlSerializerProvider.serializeValue(XmlSerializerProvider.java:92)
    at com.fasterxml.jackson.databind.ObjectWriter._configAndWriteValue(ObjectWriter.java:809)
    at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:633)
    at com.nuecho.desjardins.CsvConfigLoader.main(CsvConfigLoader.java:355)
Caused by: javax.xml.stream.XMLStreamException: Trying to write an attribute when there is no open start element.
    at com.ctc.wstx.sw.BaseStreamWriter.throwOutputError(BaseStreamWriter.java:1522)
    at com.ctc.wstx.sw.RepairingNsStreamWriter.writeAttribute(RepairingNsStreamWriter.java:110)
    at com.fasterxml.jackson.dataformat.xml.ser.ToXmlGenerator.writeString(ToXmlGenerator.java:482)
    ... 20 more

[pgelinas]

As a note, this happens when trying to write an object as a reference, only the id and not the full object.

[pgelinas]

I found two ways to fix this issue:

• the assumption to generate the "type" property as an xml attribute is removed. This is the easiest code modification, but it changes how the Xml is serialized. Not a big deal, IMHO.
• Change BeanSerializerBase to enable sub-class to modify the object id serialization processing flow. Basically, this require either removing the "final" modifier on _serializeWithObjectId or extracting the bottom part of that method (starting at String typeStr = (_typeId == null) ? null :_customTypeId(bean);) into a new method, which isn't final. This is still relatively simple to do, but it changes a little bit the API so dataformat-xml 2.3.1 would require databind 2.3.1 and not 2.3.0 anymore, so I don't know if this is possible for a patch version.

Currently, I've built locally a SNAPSHOT version of databind and dataformat xml with the second solution and using that in the project, and it works pretty well.

[lightbringer]

This seems to be a pretty old issue, but I've just encountered it in 2.8.9:

@JsonIdentityInfo( generator = ObjectIdGenerators.IntSequenceGenerator.class, property = "id" )
@JacksonXmlRootElement( localName = "a" )
public class A {
    public static void main( String[] args ) throws IOException {
        final A a = new A();
        a.b = new B(); //B has a reference back to A
        a.b.setA( a );
        
        final XmlMapper mapper = new XmlMapper();
        final String json = mapper.writeValueAsString( a );
        System.out.println( json );
    }

    private B b;

    private String name = "test";

    
    @JacksonXmlProperty( isAttribute = true ) //test runs with isAttribute set to false (but serializes name as an elment
    public String getName() {
        return name;
    }
 //other getter/setter omitted for brevity    

Expected output:

<a name="test">
<id>1</id>
<b>
<a>1</a>
</b>
</a>

Instead the exception:

Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Unexpected IOException (of type java.io.IOException): javax.xml.stream.XMLStreamException: Trying to write an attribute when there is no open start element.
at com.fasterxml.jackson.databind.JsonMappingException.fromUnexpectedIOE(JsonMappingException.java:333)
at com.fasterxml.jackson.databind.ObjectMapper.writeValueAsString(ObjectMapper.java:3077)
at test.A.main(A.java:20)

is thrown. Removing the JsonIdentityInfo annotation solves the issue as well, i.e. name is serialized as an attribute, but then the circular reference causes a stack overflow.