Java Record XML反序列化报错：No fallback setter/field定义问题求助

使用Jackson 2.18.0处理Java Record的XML反序列化时抛出InvalidDefinitionException，提示No fallback setter/field defined for creator property 'accesslevel'，相关代码及异常信息如下：

测试代码 #

var xml = """
        <person>
            <accesslevels>
                <accesslevel>Level1</accesslevel>
                <accesslevel>Level2</accesslevel>
            </accesslevels>
        </person>
        """.trim();
var mapper = new XmlMapper();
Person person = mapper.readValue(xml, Person.class);

Person Record定义 #

public record Person(
        @JacksonXmlElementWrapper(useWrapping = false)
        @JacksonXmlProperty(localName = "accesslevels")
        List<AccessLevel> accessLevels
) {
}

AccessLevel Record定义 #

public record AccessLevel(
        @JacksonXmlProperty(localName = "accesslevel")
        String accessLevel
) {
}

异常信息 #

Exception in thread "main" com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No fallback setter/field
 defined for creator property 'accesslevel' (of `com.example.person.AccessLevel`)
 (through reference chain: com.example.person.Person["accesslevels"]->java.util.ArrayList[0]->
 com.example.person.AccessLevel["accesslevel"])
    at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67)
    at com.fasterxml.jackson.databind.deser.CreatorProperty._reportMissingSetter(CreatorProperty.java:358)
    at com.fasterxml.jackson.databind.deser.CreatorProperty._verifySetter(CreatorProperty.java:341)
    at com.fasterxml.jackson.databind.deser.CreatorProperty.deserializeAndSet(CreatorProperty.java:270)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:273)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeUsingPropertyBased(BeanDeserializer.java:472)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1497)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:348)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:185)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer._deserializeFromArray(CollectionDeserializer.java:361)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:246)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:30)
    at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:543)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeWithErrorWrapping(BeanDeserializer.java:578)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeUsingPropertyBased(BeanDeserializer.java:447)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1497)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:348)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:185)
    at com.fasterxml.jackson.dataformat.xml.deser.WrapperHandlingDeserializer.deserialize(WrapperHandlingDeserializer.java:122)
    at com.fasterxml.jackson.dataformat.xml.deser.XmlDeserializationContext.readRootValue(XmlDeserializationContext.java:104)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4917)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3860)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3828)
    at com.example.Main.main(Main.java:18)

解决思路 #

1. 修正AccessLevel的注解映射 #

XML中的<accesslevel>是直接包含文本内容的元素，而非嵌套对象。之前用@JacksonXmlProperty会让Jackson误以为要映射子元素，导致找不到对应的属性。需要改用@JacksonXmlText标记该字段是XML元素的文本内容：

public record AccessLevel(
        @JacksonXmlText
        String accessLevel
) {
}

2. 调整Person的集合映射注解 #

原来的注解组合错误，@JacksonXmlElementWrapper(useWrapping = false)会关闭集合的外层包裹，但XML里明确有<accesslevels>作为外层容器。正确的配置是用@JacksonXmlElementWrapper指定外层容器名，@JacksonXmlProperty指定集合元素对应的XML标签：

public record Person(
        @JacksonXmlElementWrapper(localName = "accesslevels")
        @JacksonXmlProperty(localName = "accesslevel")
        List<AccessLevel> accessLevels
) {
}

3. 验证修改 #

调整两个Record的注解后，运行测试代码即可正常完成XML反序列化，将<accesslevels>下的多个<accesslevel>元素映射为List<AccessLevel>。

内容的提问来源于stack exchange，提问作者Philipp Grigoryev