FasterXML/jackson-databind · error · IllegalStateException

_anySetter already set to non-null

Error message

_anySetter already set to non-null

What it means

Thrown by BeanDeserializerBuilder.setAnySetter as IllegalStateException when setAnySetter is invoked twice with non-null values. A bean can have at most one 'any setter' (the catch-all for unknown properties, via @JsonAnySetter); encountering a second candidate means the type declares multiple any-setter members.

Source

Thrown at src/main/java/tools/jackson/databind/deser/BeanDeserializerBuilder.java:299

    /**
     * Method called by deserializer factory, when a "creator property"
     * (something that is passed via constructor- or factory method argument;
     * instead of setter or field).
     *<p>
     * Default implementation does not do anything; we may need to revisit this
     * decision if these properties need to be available through accessors.
     * For now, however, we just have to ensure that we don't try to resolve
     * types that masked setter/field has (see [JACKSON-700] for details).
     */
    public void addCreatorProperty(SettableBeanProperty prop)
    {
        addProperty(prop);
    }

    public void setAnySetter(SettableAnyProperty s)
    {
        if (_anySetter != null && s != null) {
            throw new IllegalStateException("_anySetter already set to non-null");
        }
        _anySetter = s;
    }

    public void setIgnoreUnknownProperties(boolean ignore) {
        _ignoreAllUnknown = ignore;
    }

    public void setValueInstantiator(ValueInstantiator inst) {
        _valueInstantiator = inst;
        _propsBasedCreatorParams = inst.getFromObjectArguments(_config);
    }

    public void setObjectIdReader(ObjectIdReader r) {
        _objectIdReader = r;
    }

    public void setPOJOBuilder(AnnotatedMethod buildMethod, JsonPOJOBuilder.Value config) {

View on GitHub (pinned to 87876ca5c0)

Solutions

1. Ensure the target type declares exactly one @JsonAnySetter member (typically a single-arg Map setter or a (String, Object) method).
2. Remove redundant @JsonAnySetter annotations after refactoring.
3. Check mixins applied to the type do not add a second any-setter.

Example fix

// before: two any-setters
class Pojo {
    @JsonAnySetter private Map<String,Object> extra;
    @JsonAnySetter public void add(String k, Object v){...}
}

// after: single any-setter
class Pojo {
    @JsonAnySetter public void add(String k, Object v){...}
}

// Count @JsonAnySetter members on the type (and mixins).
long anySetters = Arrays.stream(cls.getDeclaredMethods())
    .filter(m -> m.isAnnotationPresent(JsonAnySetter.class)).count();
if (anySetters > 1) {
    throw new IllegalStateException(cls + " has multiple @JsonAnySetter methods");
}

When it happens

Trigger: A bean declares more than one @JsonAnySetter (e.g., a field of type Map plus a setter method, or two any-setter methods), causing the factory to call setAnySetter twice with non-null.

Common situations: Adding @JsonAnySetter to both a Map field and a method; refactoring a setter into a field but leaving the old annotation; mixins/merged types that collectively declare two any-setters; combining @JsonAnySetter with @JsonSetter on the same logical slot.

Related errors

• Duplicate property '${prop.getName()}' for ${_beanDescRef.ge
• Invalid Object Id definition for %s: cannot find property wi
• Unsuitable method ({}) decorated with @JsonCreator (for Enum
• Cannot deserialize Class ${type.getName()} (of type ${typeSt
• Cannot deserialize Proxy class ${type.getName()} as a Bean

AI-assisted analysis of FasterXML/jackson-databind@87876ca5c0 (2026-08-11). Data as JSON: /api/errors/920ca1ee467b3b9a. Report an issue: GitHub.