Home/ Questions/Q 6768061
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-26T15:01:42+00:00

I am using Jackson to serialize a JAXB annotated object into a map object.

  • 0

I am using Jackson to serialize a JAXB annotated object into a map object. Here is some code to illustrate my problem:

    public class Test {

    @XmlAccessorType(XmlAccessType.NONE)
    public static class Inner {
        @XmlAttribute
        public int foo;
    }

    @XmlAccessorType(XmlAccessType.NONE)
    public static class Outer {
        @XmlAttribute
        public String bar;

        @XmlElement
        public Inner in;
    }

    public static void main(String[] args) throws Exception {
        ObjectMapper mapper = getMapper();

        mapper.enableDefaultTyping();

        Inner in = new Inner();
        in.foo = 42;
        Outer out = new Outer();
        out.in = in;
        out.bar = "thecakeisalie";

        Object o = mapper.convertValue(out, TreeMap.class);
        System.out.println(o);
    }

    public static ObjectMapper getMapper() {
        ObjectMapper mapper = new ObjectMapper();
        AnnotationIntrospector introspector = new JaxbAnnotationIntrospector();
        mapper.setAnnotationIntrospector(introspector);
        return mapper;
    }
}

This results in the following error:

Exception in thread "main" java.lang.IllegalArgumentException: Unexpected token (START_OBJECT), expected START_ARRAY: need JSON Array to contain As.WRAPPER_ARRAY type information for class java.lang.Object
 at [Source: N/A; line: -1, column: -1]
    at org.codehaus.jackson.map.ObjectMapper._convert(ObjectMapper.java:2493)
    at org.codehaus.jackson.map.ObjectMapper.convertValue(ObjectMapper.java:2459)
    at com.example.test.Test.main(Test.java:49)
Caused by: org.codehaus.jackson.map.JsonMappingException: Unexpected token (START_OBJECT), expected START_ARRAY: need JSON Array to contain As.WRAPPER_ARRAY type information for class java.lang.Object
 at [Source: N/A; line: -1, column: -1]
    at org.codehaus.jackson.map.JsonMappingException.from(JsonMappingException.java:163)
    at org.codehaus.jackson.map.deser.StdDeserializationContext.wrongTokenException(StdDeserializationContext.java:261)
    at org.codehaus.jackson.map.jsontype.impl.AsArrayTypeDeserializer._locateTypeId(AsArrayTypeDeserializer.java:100)
    at org.codehaus.jackson.map.jsontype.impl.AsArrayTypeDeserializer._deserialize(AsArrayTypeDeserializer.java:86)
    at org.codehaus.jackson.map.jsontype.impl.AsArrayTypeDeserializer.deserializeTypedFromAny(AsArrayTypeDeserializer.java:69)
    at org.codehaus.jackson.map.deser.std.UntypedObjectDeserializer.deserializeWithType(UntypedObjectDeserializer.java:106)
    at org.codehaus.jackson.map.deser.std.MapDeserializer._readAndBind(MapDeserializer.java:321)
    at org.codehaus.jackson.map.deser.std.MapDeserializer.deserialize(MapDeserializer.java:249)
    at org.codehaus.jackson.map.deser.std.MapDeserializer.deserialize(MapDeserializer.java:33)
    at org.codehaus.jackson.map.ObjectMapper._readValue(ObjectMapper.java:2695)
    at org.codehaus.jackson.map.ObjectMapper.readValue(ObjectMapper.java:1308)
    at org.codehaus.jackson.map.ObjectMapper._convert(ObjectMapper.java:2489)
    ... 2 more

If the line mapper.enableDefaultTyping(); is omitted, the code works and outputs the following:

{bar=thecakeisalie, in={foo=42}}

If I use the mapper to serialize to json, it will work with default typing.

Is default typing incompatible with object conversions, or am I using it wrong?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    Ok. Hmmh. The problem stems from sort of incompatible usage: what happens is that when serializing, default typing will only add type information as per its configuration, and in this case type information is not included (types are not abstract, nor declared as java.lang.Object).
    But when deserializing (as part of conversion), result type expects type information, since nominal type is TreeMap<Object,Object>; and that’s where exception comes from.

    But since you are converting to a Map — which is essentially an “untyped” type — you are best off just not enabling default typing. That type information would be discarded anyway.

    Or, if you really want to see that included type information, you need to do two-phase processing: serialize with default typing enabled (using mapper that has it enabled), and deserialize as TreeMap, with ObjectMapper that has default typing disabled.

    • 0