Read embedded object in Jackson

Question

I\'m trying to read a legacy JSON code using Jackson 2.0-RC3, however I\'m stuck with an \"embedded\" object.

Given a following JSON:

{
    \"title\"         


        

Answer 1

Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB 2 (JSR-222) expert group.

I'm not sure if Jackson supports this use case, but below is an example of how you can leverage MOXy's @XmlPath extension to meet your requirements. Note you will need to use an EclipseLink 2.4.0 nightly label from April 7, 2012 or newer.

• http://www.eclipse.org/eclipselink/downloads/nightly.php

Item

The author property on Item is mapped with @XmlPath('.'). This means that the content of Author is pulled up to the same level as the content for Item. I also needed to use an XmlAdapter for the Date property as the format you are using doesn't match MOXy's default representation.

package forum10036530;

import java.util.Date;
import javax.xml.bind.annotation.*;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
import org.eclipse.persistence.oxm.annotations.XmlPath;

@XmlAccessorType(XmlAccessType.FIELD)
class Item {
    private String title;

    @XmlElement(name="date")
    @XmlJavaTypeAdapter(DateAdapter.class)
    private Date createdAt;

    @XmlPath(".")
    private Author author;
}

Author

package forum10036530;

import java.net.URL;
import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
class Author {
    @XmlElement(name="author")
    private String name;

    @XmlElement(name="author_avatar")
    private URL avatar;

    @XmlElement(name="author_group")
    private Integer group;

    @XmlElement(name="author_prop")
    private String prop;
}

DateAdapter

package forum10036530;

import java.text.SimpleDateFormat;
import java.util.Date;
import javax.xml.bind.annotation.adapters.XmlAdapter;

public class DateAdapter extends XmlAdapter<String, Date> {

    private SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");

    @Override
    public Date unmarshal(String string) throws Exception {
        return dateFormat.parse(string);
    }

    @Override
    public String marshal(Date date) throws Exception {
        return dateFormat.format(date);
    }

}

jaxb.properties

A file called jaxb.properties with the following entry must be placed in the same package as the domain classes to specify MOXy as the JAXB (JSR-222) provider.

javax.xml.bind.context.factory = org.eclipse.persistence.jaxb.JAXBContextFactory

input.json/Output

{
   "title" : "Hello world!",
   "date" : "2012-02-02 12:23:34",
   "author" : "username",
   "author_avatar" : "http://www.example.com/foo.png",
   "author_group" : 123,
   "author_prop" : "value"
}

For More Information

• http://blog.bdoughan.com/2010/07/xpath-based-mapping.html
• http://blog.bdoughan.com/2011/08/json-binding-with-eclipselink-moxy.html
• http://blog.bdoughan.com/2011/08/binding-to-json-xml-geocode-example.html

Answer 2

I would deserialize the original JSON to a single, flat object first (kind of like an adapter), then create your own domain objects.

class ItemLegacy {
    private String title;

    @JsonProperty("date")
    private Date createdAt;

    @JsonPropery("author")
    private String name;

    @JsonPropery("author_avatar")
    private URL avatar;

    @JsonProperty("author_group")
    private Integer group;

    @JsonProperty("author_prop")
    private Integer group;
}

Then use this object to fill out your Item and Author objects and create the correct relationships.

 //... the deserialized original JSON
 ItemLegacy legacy ...

 // create an author
 Author author = new Author();
 author.setName(legacy.getName());
 author.setGroup(legacy.getGroup());
 ...

 // create an item
 Item item = new Item();
 item.setTitle(legacy.getTitle());
 ...

 // finally set the author... and you should have the desired structure
 item.setAuthor(author);

Your Item class could only be automatically deserialized from the following form:

{
    "title": "Hello world!",
    "date": "2012-02-02 12:23:34".
    "author": { 
                "name": "username", 
                "author_avatar": "http://...", 
                "author_group": "123", 
                "author_prop": "value" 
              }
}

You might be able to do something with custom deserialization, but it would not be the simpler solution for sure.

Answer 3

To deal with an "embedded" object you should use @JsonUnwrapped — it's an equivalent of the Hibernate's @Embeddable/@Embedded.

class Item {
    private String title;

    @JsonProperty("date")
    private Date createdAt;

    // How to map this?
    @JsonUnwrapped
    private Author author;
}