Jackson: XML to Map with List deserialization

Question

Is there a way to deserialize the following xml into Map holding List of items using Jackson?

<order>
    <number>12345678</number>
    <amount>100.10</amount>
    <items>
        <item>
            <itemId>123</itemId>
            <amount>100.0</amount>
            <itemName>Item Name1</itemName>
        </item>
        <item>
            <itemId>234</itemId>
            <amount>200.00</amount>
            <itemName>Item Name1</itemName>
        </item>
    </items>
</order>

I tried with

XmlMapper mapper = new XmlMapper();
LinkedHashMap map = (LinkedHashMap)mapper.readValue(xml, Object.class);

and got the following Map. The first item in the list is missing.

{
    order={
        number=12345678,
        amount=100.1,
        items={
            item={
                amount=200.0,
                itemName=ItemName2,
                itemId=234
            }
        }
    }
}

I do not want to use POJO to hold order data. The idea here is to use Map and List as a generic data structure. — Raj, Dec 19 '12 at 23:03
This "problem" also occurs when one uses `mapper.readTree(xml);` which one might hope builds a tree map — Richard Donovan, Sep 12 '13 at 18:27

Volkan Yazıcı · Answer 1 · 2018-09-14T19:24:44.767

This is a known jackson-dataformat-xml bug filed under issue 205. In a nutshell, duplicated elements in the XML get swallowed by the current UntypedObjectDeserializer implementation. Fortunately, the author (João Paulo Varandas) of the report also provided a temporary fix in the form a custom UntypedObjectDeserializer implementation. Below I share my interpretation of the fix:

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.deser.std.UntypedObjectDeserializer;
import com.fasterxml.jackson.databind.module.SimpleModule;
import com.fasterxml.jackson.dataformat.xml.XmlMapper;

import javax.annotation.Nullable;
import java.io.IOException;
import java.util.*;

public enum JacksonDataformatXmlIssue205Fix {;

    public static void main(String[] args) throws IOException {
        String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
                "<items>\n" +
                "    <item><id>1</id></item>\n" +
                "    <item><id>2</id></item>\n" +
                "    <item><id>3</id></item>\n" +
                "</items>";
        SimpleModule module = new SimpleModule().addDeserializer(Object.class, Issue205FixedUntypedObjectDeserializer.getInstance());
        XmlMapper xmlMapper = (XmlMapper) new XmlMapper().registerModule(module);
        Object object = xmlMapper.readValue(xml, Object.class);
        System.out.println(object);     // {item=[{id=1}, {id=2}, {id=3}]}
    }

    @SuppressWarnings({ "deprecation", "serial" })
    public static class Issue205FixedUntypedObjectDeserializer extends UntypedObjectDeserializer {

        private static final Issue205FixedUntypedObjectDeserializer INSTANCE = new Issue205FixedUntypedObjectDeserializer();

        private Issue205FixedUntypedObjectDeserializer() {}

        public static Issue205FixedUntypedObjectDeserializer getInstance() {
            return INSTANCE;
        }

        @Override
        @SuppressWarnings({ "unchecked", "rawtypes" })
        protected Object mapObject(JsonParser parser, DeserializationContext context) throws IOException {

            // Read the first key.
            @Nullable String firstKey;
            JsonToken token = parser.getCurrentToken();
            if (token == JsonToken.START_OBJECT) {
                firstKey = parser.nextFieldName();
            } else if (token == JsonToken.FIELD_NAME) {
                firstKey = parser.getCurrentName();
            } else {
                if (token != JsonToken.END_OBJECT) {
                    throw context.mappingException(handledType(), parser.getCurrentToken());
                }
                return Collections.emptyMap();
            }

            // Populate entries.
            Map<String, Object> valueByKey = new LinkedHashMap<>();
            String nextKey = firstKey;
            do {

                // Read the next value.
                parser.nextToken();
                Object nextValue = deserialize(parser, context);

                // Key conflict? Combine existing and current entries into a list.
                if (valueByKey.containsKey(nextKey)) {
                    Object existingValue = valueByKey.get(nextKey);
                    if (existingValue instanceof List) {
                        List<Object> values = (List<Object>) existingValue;
                        values.add(nextValue);
                    } else {
                        List<Object> values = new ArrayList<>();
                        values.add(existingValue);
                        values.add(nextValue);
                        valueByKey.put(nextKey, values);
                    }
                }

                // New key? Put into the map.
                else {
                    valueByKey.put(nextKey, nextValue);
                }

            } while ((nextKey = parser.nextFieldName()) != null);

            // Ship back the collected entries.
            return valueByKey;

        }

    }

}

What about UntypedObjectDeserializer's constructor being deprecated? — Evgeni Atanasov, Apr 02 '19 at 15:51
Good approach! I use similar approach but with guava multimap plus special configured writer. https://stackoverflow.com/a/62468955/1485527 — jschnasse, Jun 29 '20 at 11:03

score 2 · Answer 2 · answered Aug 11 '19 at 15:20

The other answers don't work if you have to use readTree() and JsonNode. I know it's an ugly solution but at least you don't need to paste someone's gist in your project.

Add org.json to your project dependencies.

And then do the following:

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.json.JSONObject;
import org.json.XML;
...
private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
...
    JSONObject soapDatainJsonObject = XML.toJSONObject(data);
    return OBJECT_MAPPER.readTree(soapDatainJsonObject.toString());

The conversion goes as follows:

XML -> JSONObject (using org.json) -> string -> JsonNode (using readTree)

Of course, toJSONObject handles duplicates without any problems, I suggest to avoid using Jackson and readTree() if you can.

score 0 · Answer 3 · answered Dec 25 '12 at 21:36

0

Created a custom deserializer by extending UntypedObjectDeserializer to do this job.

answered Dec 25 '12 at 21:36

Raj

209
2
4

2

can you expand on that answer? It would be greatly appreciated – Richard Donovan Sep 12 '13 at 18:26

score 0 · Answer 4 · answered Nov 01 '22 at 13:50

If you aren't tied to Jackson, underscore-java will do this very nicely:

import com.github.underscore.U;
import java.util.Map;

public class MyClass {
    public static void main(String args[]) {
      Map map = U.fromXmlMap(
          "<order>\r\n" +
            "<number>12345678</number>\r\n" +
            "<amount>100.10</amount>\r\n" +
            "<items>\r\n" +
                "<item>\r\n" +
                    "<itemId>123</itemId>\r\n" +
                    "<amount>100.0</amount>\r\n" +
                    "<itemName>Item Name1</itemName>\r\n" +
                "</item>\r\n" +
                "<item>\r\n" +
                    "<itemId>234</itemId>\r\n" +
                    "<amount>200.00</amount>\r\n" +
                    "<itemName>Item Name1</itemName>\r\n" +
                "</item>\r\n" +
            "</items>\r\n" +
        "</order>"
      );
      System.out.println(map);
      // {order={number=12345678, amount=100.10, items={item=[{itemId=123, amount=100.0, itemName=Item Name1}, {itemId=234, amount=200.00, itemName=Item Name1}]}}, #omit-xml-declaration=yes}
    }
}

Jackson: XML to Map with List deserialization

4 Answers4

Linked