Using Jackson to add XML attributes to manually-built node-tree

Question

I'm trying to set up code to create a node tree using Jackson which can then be used to write either JSON or XML. I've created the node tree manually like so:

XmlMapper nodeMapper = new XmlMapper();

ObjectNode rootNode = nodeMapper.createObjectNode();
ObjectNode currentNode = rootNode.putObject("Examples");
currentNode.put("Puppy", TRUE)
           .put("Apple", 2)
           .put("Jet", "Li");
currentNode = rootNode.putObject("Single");
currentNode.put("One", 1);

String writePath = "C:/users/itsameamario/Documents/basicXMLtest.xml";
nodeMapper.writeValue(new File(writePath), rootNode);

My XML output is:

<?xml version="1.0"?>
<ObjectNode>
    <Examples>
        <Puppy>true</Puppy>
        <Apple>2</Apple>
        <Jet>Li</Jet>
    </Examples>
    <Single>
        <One>1</One>
    </Single>
</ObjectNode>

However for some parts of the XML I would like to add an attribute to one of the nodes like so:

<Examples overlyComplicated="yes">
<!--...-->
</Examples>

All the examples I've found that include attributes are applied to a pre-existing class. I have been unable to find a method to add attributes to a manually-built node-tree as above. Is it doable using Jackson?

score 8 · Accepted Answer · answered Jul 17 '19 at 00:02

It is not possible to mark given property as attribute since ObjectNode does not know anything about the serialisation. You can do that for POJO class and com.fasterxml.jackson.dataformat.xml.ser.ToXmlGenerator will handle it only if @JacksonXmlProperty(isAttribute = true) annotation is used for given property. I suggest to create POJO for element where you need attribute and use Jackson XML annotations or implement JsonSerializable interface. It could look like below:

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializable;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.jsontype.TypeSerializer;
import com.fasterxml.jackson.databind.node.ObjectNode;
import com.fasterxml.jackson.dataformat.xml.XmlMapper;
import com.fasterxml.jackson.dataformat.xml.ser.ToXmlGenerator;

import java.io.IOException;
import java.util.LinkedHashMap;
import java.util.Map;

public class XmlMapperApp {

    public static void main(String[] args) throws Exception {
        Map<String, Object> map = new LinkedHashMap<>();
        map.put("Puppy", Boolean.TRUE);
        map.put("Apple", 2);
        map.put("Jet", "Li");
        Examples examples = new Examples();
        examples.setOverlyComplicated("yes");
        examples.setMap(map);

        XmlMapper mapper = new XmlMapper();
        mapper.enable(SerializationFeature.INDENT_OUTPUT);

        ObjectNode rootNode = mapper.createObjectNode();
        rootNode.putPOJO("Examples", examples);
        ObjectNode currentNode = rootNode.putObject("Single");
        currentNode.put("One", 1);

        mapper.writeValue(System.out, rootNode);
    }
}

class Examples implements JsonSerializable {

    @Override
    public void serialize(JsonGenerator gen, SerializerProvider serializers) throws IOException {
        ToXmlGenerator toXmlGenerator = (ToXmlGenerator) gen;
        toXmlGenerator.writeStartObject();

        writeAttributes(toXmlGenerator);
        writeMap(toXmlGenerator);

        toXmlGenerator.writeEndObject();
    }

    private void writeAttributes(ToXmlGenerator gen) throws IOException {
        if (overlyComplicated != null) {
            gen.setNextIsAttribute(true);
            gen.writeFieldName("overlyComplicated");
            gen.writeString(overlyComplicated);
            gen.setNextIsAttribute(false);
        }
    }

    private void writeMap(ToXmlGenerator toXmlGenerator) throws IOException {
        for (Map.Entry<String, Object> entry : map.entrySet()) {
            toXmlGenerator.writeObjectField(entry.getKey(), entry.getValue());
        }
    }

    @Override
    public void serializeWithType(JsonGenerator gen, SerializerProvider serializers, TypeSerializer typeSer) throws IOException {
        serialize(gen, serializers);
    }

    private String overlyComplicated;
    private Map<String, Object> map;

    // getters, setters, toString
}

Above code prints:

<ObjectNode>
  <Examples overlyComplicated="yes">
    <Puppy>true</Puppy>
    <Apple>2</Apple>
    <Jet>Li</Jet>
  </Examples>
  <Single>
    <One>1</One>
  </Single>
</ObjectNode>

In case you want to use the same Example POJO for JSON serialisation you need to handle it in serialize method or create another ObjectNode instead of Examlples object.

Using Jackson to add XML attributes to manually-built node-tree

1 Answers1

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