jackson custom deserializer only getting last value in list xml

Question

I have the following xml

<root>
<date>112004</date>
<entries>
    <entry id = 1>
        <status>Active</status>
        <person>
            <Name>John</Name>
            <Age>22</Age>
        </person>
    </entry>
    <entry id = 2>
        <status>Active</status>
        <person>
            <Name>Doe</Name>
            <Age>32</Age>
        </person>
    </entry>
    <entry id = 3>
        <status>N/A</status>
    </entry>
</entries>

I am using custom jackson deserializer to get the values and pojo looks like

@JacksonXmlRootElement(localName="root", namespace="namespace")

class root { private String date;

@JacksonXmlProperty(localName = "entries", namespace="tns")
private List<Entry> entries;
//getter and setter

}

class Entry {
 private String id;
 private String status;
 private Person person;
 //getter and setter
}

And the deserializer code looks like

public class DeSerializer extends StdDeserializer<root>
{
 protected DeSerializer() {
    super(root.class);
  }
  @Override
public root deserialize(JsonParser p, DeserializationContext ctxt)  throws IOException, JsonProcessingException {
    JsonNode nodes = p.readValueAsTree();
    ObjectMapper mapper = new ObjectMapper();
    List<Entry> entry = mapper.convertValue(nodes.findValues("entry"), new TypeReference<List<Entry>>() {});
}
}

main()
{
XmlMapper x = new XmlMapper();
 final SimpleModule module = new SimpleModule("configModule",   com.fasterxml.jackson.core.Version.unknownVersion());
            module.addDeserializer(root.class, new DeSerializer());
            x.registerModule(module);
            root r = x.readValue(xmlSource, root.class); /*xmlsource is xml as string*/
}

The issue is when I debugged I am always getting the entry last value from xml. So the values of nodes (in deserializer) is {"date":"112004","entries":{"entry":{"id":"3","status":"N/A"}}} and I am not sure why it is not treating as list. I did add annotation of unwrapped = false for List but that did not work out.

Answer 1

It seems readValueAsTree does not support fetching whole collection.

I did some work around without custom DeSerializer which works.

@JacksonXmlRootElement(localName="root")
public class Root {
@JacksonXmlElementWrapper(useWrapping = true)
private List<Entry> entries;

private String date;

public List<Entry> getEntries() {
    return entries;
}

public void setEntries(List<Entry> entries) {
    if (this.entries == null){
        this.entries = new ArrayList<>(entries.size());
    }
    this.entries.addAll(entries);
}

public String getDate() {
    return date;
}

public void setDate(String date) {
    this.date = date;
}
}

class Entry {
private String id;
private String status;
private Person person;
}

class Person {
@JacksonXmlProperty(localName = "Name")
private String name;

@JacksonXmlProperty(localName = "Age")
private String age;
}

Then unit test:

    @Test
    void test_xml_XmlMapper() throws Exception {
    JacksonXmlModule xmlModule = new JacksonXmlModule();
    xmlModule.setDefaultUseWrapper(false);
    ObjectMapper xmlMapper = new XmlMapper(xmlModule);

    String xmlContent = "your xml file here"
    Root bean = xmlMapper.readValue(xmlContent, Root.class);
    assertThat(bean.getEntries().size(), Matchers.equalTo(3));
}

Answer 2

I can see why the answer by @stephen-hazra is downvoted, because he doesn't really answer the question, however: He is right.

I don't know the exact from version, but up until 2.11.x custom deserialization of an Array in an xml was broken. If we take the xml from the question and implemented a Deserializer and used it like this:

@JsonDeserialize(using = MyDeserializer.class)
private List<MyClass> entries = new ArrayList<>();

If the MyDeserializer class extended from StdSerializer, also like in the question, the deserialize method would always only ever get the last child "entry"-element from the children of entries to process.

In later versions this is fixed, you can now implement the deserialize method like follows:

@Override
public List<MyClass> deserialize(JsonParser jsonParser, DeserializationContext ctxt) throws IOException {
    final List<MyClass> result = new ArrayList<>();
    final ObjectNode node = jsonParser.getCodec().readTree(jsonParser);
    //entry and extendedEntry are different children in the xml that can be parsed as MyClass
    processNode((ContainerNode) node.get("entry"), jsonParser, result);
    processNode((ContainerNode) node.get("extendedEntry"), jsonParser, result);
    return result;
}

private void processNode(ContainerNode cNode, JsonParser jsonParser, List<MyClass> result) throws IOException {
    if (cNode == null) return;
    //cNode can either be an ObjectNode or an ArrayNode based on how many children there can be found in the xml.
    if (cNode.isArray()) { cNode.iterator().forEachRemaining(node -> {
        try {
            result.add(node.traverse(jsonParser.getCodec()).readValueAs(MyClass.class));
            } catch (IOException e) {
              //whatever
            }
        });
    } else {
        result.add(cNode.traverse(jsonParser.getCodec()).readValueAs(MyClass.class));
    }
}
    

I'm writing this example down as answer, because I was basically stuck a whole afternoon, wondering how I could process these other child elements in my xml, because in my case I also had children in the xml with different tag names, but same content type, so parsing just the content with contentUsing was not sufficient, because that way I lost important information based on the original tag name of the child. And in the end it just turned out that the jackson version 2.11 I was using, was just broken in that regard. So thanks to Stephen for pointing me into that direction.

Answer 3

If someone is still facing this issue, please upgrade to the latest jackson 2.12.3 version. I was facing this issue in 2.11.x version.