JAXB and JSON via Jettison - Namespace Example

In a previous post I described how Jettison can be leveraged by a JAXB implementation to produce/consume JSON.  A reader correctly pointed out that I did not describe how to handle namespaces.  Since JSON does not support namespaces you would not normally include them in your mappings.  However if you wanted to map your object model to both JSON and XML with namespaces, this post will demonstrate how it can be done.

Java Model

The following Java class will be used for the domain model in this example.

package-info

@XmlSchema(
    namespace = "http://www.example.org/package",
    elementFormDefault = XmlNsForm.QUALIFIED) 
package blog.json.ns;

import javax.xml.bind.annotation.XmlSchema;
import javax.xml.bind.annotation.XmlNsForm;

Customer

package blog.json.ns;

import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
 
@XmlRootElement
public class Customer {
 
    private long id;
    private String name;
 
    @XmlAttribute
    public long getId() {
        return id;
    }
 
    public void setId(long id) {
        this.id = id;
    }
 
    @XmlElement(namespace="http://www.example.org/property")
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
}

XML Input

The JAXB metadata we have applied to our domain model, allow us to interact with the XML document below.  We will use the following XML document to populate our domain model.

<ns:customer
    xmlns="http://www.example.org/property"
    xmlns:ns="http://www.example.org/package"
    id="123">
    <name>Jane Doe</name>
</ns:customer>

Marshal Demo

Jettison works by exposing StAX interfaces to JSON data.  Since JAXB knows how to deal with StAX interfaces we can easily marshal to them.  To handle the namespaces we will leverage the Config object.  On the Config object we can set a Map of namespaces to JSON prefixes.

package blog.json.ns;

import java.io.File;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.util.HashMap;
import java.util.Map;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import javax.xml.stream.XMLStreamWriter;

import org.codehaus.jettison.mapped.Configuration;
import org.codehaus.jettison.mapped.MappedNamespaceConvention;
import org.codehaus.jettison.mapped.MappedXMLStreamWriter;

public class MarshalDemo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Customer.class);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        Customer customer = (Customer) unmarshaller.unmarshal(new File("src/blog/json/ns/input.xml"));

        Configuration config = new Configuration();
        Map<String, String> xmlToJsonNamespaces = new HashMap<String,String>(1);
        xmlToJsonNamespaces.put("http://www.example.org/package", "");
        xmlToJsonNamespaces.put("http://www.example.org/property", "prop");
        config.setXmlToJsonNamespaces(xmlToJsonNamespaces);
        MappedNamespaceConvention con = new MappedNamespaceConvention(config);
        Writer writer = new OutputStreamWriter(System.out);
        XMLStreamWriter xmlStreamWriter = new MappedXMLStreamWriter(con, writer);

        Marshaller marshaller = jc.createMarshaller();
        marshaller.marshal(customer, xmlStreamWriter);
    }

}

JSON Output

The following JSON was produced.  Note how the nodes corresponding to the 

"http://www.example.org/property" namespace are prefixed with "prop.". The "prop." prefix was what we specified on the Config object.

{"customer":{"@id":"123","prop.name":"Jane Doe"}}

Unmarshal Demo

Similar to the marshal use case, we we will unmarshal from a Jettison object (MappedXMLStreamReader) that implements the StAX interface XMLStreamReader.  Again the Config object is leveraged to specify namespace mappings.

package blog.json.ns;

import java.util.HashMap;
import java.util.Map;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import javax.xml.stream.XMLStreamReader;

import org.codehaus.jettison.json.JSONObject;
import org.codehaus.jettison.mapped.Configuration;
import org.codehaus.jettison.mapped.MappedNamespaceConvention;
import org.codehaus.jettison.mapped.MappedXMLStreamReader;

public class UnmarshalDemo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Customer.class);

        JSONObject obj = new JSONObject("{\"customer\":{\"@id\":\"123\",\"prop.name\":\"Jane Doe\"}}");
        Configuration config = new Configuration();
        Map<String, String> xmlToJsonNamespaces = new HashMap<String,String>(1);
        xmlToJsonNamespaces.put("http://www.example.org/package", "");
        xmlToJsonNamespaces.put("http://www.example.org/property", "prop");
        config.setXmlToJsonNamespaces(xmlToJsonNamespaces);
        MappedNamespaceConvention con = new MappedNamespaceConvention(config);
        XMLStreamReader xmlStreamReader = new MappedXMLStreamReader(obj, con);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        Customer customer = (Customer) unmarshaller.unmarshal(xmlStreamReader);

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(customer, System.out);
    }

}

Further Reading

If you enjoyed this post you may also be interested in: 

• JAXB and JSON via Jettison
• JAXB & Namespaces