Binding a child object of an XmlElement list to a Java object using Jackson XmlMapper

Question

Given the following xml:

<?xml version="1.0" encoding="utf-8"?>
<live_schedules>
    <title>This Schedule</title>
    <date>20190328</date>
    <link>/v2/schedule</link>
    <id>schedule</id>
    <updated>2019-03-28T21:51:41+0</updated>
    <schedule>
        <sport id="1" name="Football" link="/v2/sport/1">
            <league id="100" name="Alliance of American Football" link="/v2/league/100" />
            <league id="101" name="Alliance of American Football" link="/v2/league/101" />
        </sport>
    </schedule>
</live_schedules>

And also given the following classes:

LiveScheduleDto.java

package com.stackoverflow.dto;

import lombok.AllArgsConstructor;
import lombok.Data;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

@Data
@AllArgsConstructor
@XmlRootElement(name = "live_schedule")
@XmlAccessorType(XmlAccessType.FIELD)
public class LiveScheduleWrapper {

    @XmlElement(name = "title")
    private String title;

    @XmlElement(name = "date")
    private String date;

    @XmlElement(name = "link")
    private String link;

    @XmlElement(name = "id")
    private String id;

    @XmlElement(name = "updated")
    private String updatedDate;

    @XmlElement(name = "schedule")
    private ScheduleDto schedule;
}

ScheduleDto.java

package com.stackoverflow.dto;

import lombok.AllArgsConstructor;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import java.util.List;

@AllArgsConstructor
@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement(name = "schedule")
class ScheduleDto {

    @XmlElement(name = "sport")
    List<SportDto> sports;
}

SportDto.java

package com.stackoverflow.dto;

import lombok.AllArgsConstructor;
import lombok.Data;

import javax.xml.bind.annotation.*;
import java.util.List;

@Data
@AllArgsConstructor
@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement(name = "sport")
public class SportDto {

    @XmlAttribute(name = "id")
    Integer id;

    @XmlAttribute(name = "name")
    String name;

    @XmlAttribute(name = "link")
    String link;

    @XmlElementWrapper(name = "league")
    List<LeagueDto> league;
}

LeagueDto.java

package com.stackoverflow.dto;

import lombok.AllArgsConstructor;

import javax.xml.bind.annotation.*;

@AllArgsConstructor
@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement(name = "league")
public class LeagueDto {

    @XmlAttribute(name = "id")
    String id;

    @XmlAttribute(name = "name")
    String name;

    @XmlAttribute(name = "link")
    String link;
}

The adaptor that performs the mapping:

package com.stackoverflow.adaptors;

import com.fasterxml.jackson.dataformat.xml.XmlMapper;
import com.fasterxml.jackson.module.jaxb.JaxbAnnotationModule;
import com.stackoverflow.dto.LiveScheduleWrapper;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;

import java.io.IOException;

public class ScheduleAdaptor {

    private final HttpClient httpClient;
    private final HttpGet httpGet;

    public ScheduleAdaptor(HttpClient httpClient, HttpGet httpGet) {
        this.httpClient = httpClient;
        this.httpGet = httpGet;
    }

    public HttpApiResponse<LiveScheduleWrapper> retrieveSchedule() {
        try {
            HttpResponse response = httpClient.execute(httpGet);
            XmlMapper mapper = new XmlMapper();
            JaxbAnnotationModule module = new JaxbAnnotationModule();
            mapper.registerModule(module);

            LiveScheduleWrapper schedule =
                    mapper.readValue(response.getEntity().getContent(), LiveScheduleWrapper.class);
            return new HttpApiResponse(response.getStatusLine().getStatusCode(), schedule);
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
}

I am seeing when I run this through a parser that it is binding the SportDto to the LeagueDto because I've defined the <sport> element as a List. This isn't what I expected. Instead I expected that it would bind the Sport XmlElement to the SportDto object then the League to the nested League object as I've defined in my example.

What's the easiest way to correctly bind the <sport> xml element list to SportDto and the <league> xml element list to the LeagueDto?

I should make it clear I'm using Jacksons XmlMapper not JAXBContext

Do you use `Jackson`'s `XmlMapper` or `JAXB`'s `JaxbContext` to deserialise `XML` to `Java` `Pojo`-s? — Michał Ziober, Apr 10 '19 at 10:51
@MichałZiober I've added an example of the code that calls the wrapper to give more context though I'm conscious that's a lot of code now. — James Murphy, Apr 10 '19 at 11:55
@MichałZiober thanks for your assistance. I needed to use the `JAXBContext` library to deserialise `XML` to `Java`. It appears it is more fully featured. — James Murphy, Apr 10 '19 at 13:14

score 0 · Answer 1 · answered Apr 10 '19 at 13:13

I managed to fix it. My issue was because I used the Jackson XmlMapper which isn't as full featured as the JAXBContext library...

I replaced my retrieveSchedule function with the following:

public HttpApiResponse<LiveScheduleWrapper> retrieveSchedule() {
    try {
        HttpResponse response = httpClient.execute(httpGet);
        JAXBContext jc = JAXBContext.newInstance(LiveScheduleWrapper.class);
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        LiveScheduleWrapper schedule = (LiveScheduleWrapper) unmarshaller.unmarshal(response.getEntity().getContent());
        return new HttpApiResponse(response.getStatusLine().getStatusCode(), schedule);
    } catch (JAXBException | IOException e) {
        e.printStackTrace();
    }
    return null;
}

This solved my issue because JAXBContext correctly recognises JAXB annotations over XmlMapper.

Binding a child object of an XmlElement list to a Java object using Jackson XmlMapper

1 Answers1