Question

I’m using JAXB with Scala, my marshalling code looks like this:

def marshalToXml(): String = {
  val context = JAXBContext.newInstance(this.getClass())
  val writer = new StringWriter
  context.createMarshaller.marshal(this, writer)
  writer.toString()
}

Then for my nullable elements I’m using the annotation @XmlElement(nillable = true) as per JAXB Marshalling with null fields. This gives me XML output like so:

<name>Alex Dean</name>
<customerReference xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
<quantity>1</quantity>
<createdAt>2011-05-14T00:00:00+03:00</createdAt>

This is a good start but what I’d really like to marshal for these fields is:

<name>Alex Dean</name>
<customerReference nil="true"/>
<quantity type="integer">1</quantity>
<createdAt type="datetime">2011-05-14T00:00:00+03:00</createdAt>

In other words, I would like to remove the namespace attributes and prefixes, and add in explicit XML datatype attributes for all but strings. It’s probably quite simple to do but I can’t seem to find how in the JAXB documentation.

Any help gratefully received!

Answer 1

You could use JAXB with a StAX parser and do the following:

Customer

Each property in your domain model will be mapped with @XmlElement(nillable=true, type=Object.class). Setting the type=Object.class will force an xsi:type attribute to be written out.

package forum8198945;

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

@XmlRootElement
public class Customer {

    private String name;
    private Customer customerReference;
    private Integer quantity;
    private Date createdAt;

    @XmlElement(nillable=true, type=Object.class)
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @XmlElement(nillable=true, type=Object.class)
    public Customer getCustomerReference() {
        return customerReference;
    }

    public void setCustomerReference(Customer customerReference) {
        this.customerReference = customerReference;
    }

    @XmlElement(nillable=true, type=Object.class)
    public Integer getQuantity() {
        return quantity;
    }

    public void setQuantity(Integer quantity) {
        this.quantity = quantity;
    }

    @XmlElement(nillable=true, type=Object.class)
    public Date getCreatedAt() {
        return createdAt;
    }

    public void setCreatedAt(Date createdAt) {
        this.createdAt = createdAt;
    }

}

XMLStreamWriterWrapper

We will write a create a wrapper for an XMLStreamWriter that strips off all the information we do not want written to XML.

package forum8198945;

import javax.xml.namespace.NamespaceContext;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamWriter;

public class XMLStreamWriterWrapper implements XMLStreamWriter {

    private XMLStreamWriter xmlStreamWriter;

    public XMLStreamWriterWrapper(XMLStreamWriter xmlStreamWriter) {
        this.xmlStreamWriter = xmlStreamWriter;
    }

    public void writeStartElement(String localName) throws XMLStreamException {
        xmlStreamWriter.writeStartElement(localName);
    }

    public void writeStartElement(String namespaceURI, String localName) throws XMLStreamException {
        xmlStreamWriter.writeStartElement(namespaceURI, localName);
    }

    public void writeStartElement(String prefix, String localName, String namespaceURI) throws XMLStreamException {
        xmlStreamWriter.writeStartElement(prefix, localName, namespaceURI);
    }

    public void writeEmptyElement(String namespaceURI, String localName) throws XMLStreamException {
        xmlStreamWriter.writeEmptyElement(namespaceURI, localName);
    }

    public void writeEmptyElement(String prefix, String localName, String namespaceURI) throws XMLStreamException {
        xmlStreamWriter.writeEmptyElement(prefix, localName, namespaceURI);
    }

    public void writeEmptyElement(String localName) throws XMLStreamException {
        xmlStreamWriter.writeEmptyElement(localName);
    }

    public void writeEndElement() throws XMLStreamException {
        xmlStreamWriter.writeEndElement();
    }

    public void writeEndDocument() throws XMLStreamException {
        xmlStreamWriter.writeEndDocument();
    }

    public void close() throws XMLStreamException {
        xmlStreamWriter.close();
    }

    public void flush() throws XMLStreamException {
        xmlStreamWriter.flush();
    }

    public void writeAttribute(String localName, String value) throws XMLStreamException {
        xmlStreamWriter.writeAttribute(localName, value);
    }

    public void writeAttribute(String prefix, String namespaceURI, String localName, String value) throws XMLStreamException {
        if("http://www.w3.org/2001/XMLSchema-instance".equals(namespaceURI)) {
            int colonIndex = value.indexOf(':');
            if(colonIndex > -1) {
                value = value.substring(colonIndex + 1);
            }
            xmlStreamWriter.writeAttribute(localName, value);
        } else {
            xmlStreamWriter.writeAttribute(prefix, namespaceURI, localName, value);
        }
    }

    public void writeAttribute(String namespaceURI, String localName, String value) throws XMLStreamException {
        if("http://www.w3.org/2001/XMLSchema-instance".equals(namespaceURI)) {
            int colonIndex = value.indexOf(':');
            if(colonIndex > -1) {
                value = value.substring(colonIndex + 1);
            }
            xmlStreamWriter.writeAttribute(localName, value);
        } else {
            xmlStreamWriter.writeAttribute(namespaceURI, localName, value);
        }
    }

    public void writeNamespace(String prefix, String namespaceURI) throws XMLStreamException {
        if(!"http://www.w3.org/2001/XMLSchema-instance".equals(namespaceURI) && !"http://www.w3.org/2001/XMLSchema".equals(namespaceURI)) {
            xmlStreamWriter.writeNamespace(prefix, namespaceURI);
        }
    }

    public void writeDefaultNamespace(String namespaceURI) throws XMLStreamException {
        if(!"http://www.w3.org/2001/XMLSchema-instance".equals(namespaceURI)) {
            xmlStreamWriter.writeDefaultNamespace(namespaceURI);
        }
    }

    public void writeComment(String data) throws XMLStreamException {
        // TODO Auto-generated method stub
    }

    public void writeProcessingInstruction(String target) throws XMLStreamException {
        // TODO Auto-generated method stub
    }

    public void writeProcessingInstruction(String target, String data) throws XMLStreamException {
        // TODO Auto-generated method stub
    }

    public void writeCData(String data) throws XMLStreamException {
        // TODO Auto-generated method stub
    }

    public void writeDTD(String dtd) throws XMLStreamException {
        // TODO Auto-generated method stub
    }

    public void writeEntityRef(String name) throws XMLStreamException {
        // TODO Auto-generated method stub
    }

    public void writeStartDocument() throws XMLStreamException {
        xmlStreamWriter.writeStartDocument();
    }

    public void writeStartDocument(String version) throws XMLStreamException {
        xmlStreamWriter.writeStartDocument(version);
    }

    public void writeStartDocument(String encoding, String version) throws XMLStreamException {
        xmlStreamWriter.writeStartDocument(encoding, version);
    }

    public void writeCharacters(String text) throws XMLStreamException {
        xmlStreamWriter.writeCharacters(text);
    }

    public void writeCharacters(char[] text, int start, int len) throws XMLStreamException {
        xmlStreamWriter.writeCharacters(text, start, len);
    }

    public String getPrefix(String uri) throws XMLStreamException {
        return xmlStreamWriter.getPrefix(uri);
    }

    public void setPrefix(String prefix, String uri) throws XMLStreamException {
        xmlStreamWriter.setPrefix(prefix, uri);
    }

    public void setDefaultNamespace(String uri) throws XMLStreamException {
        xmlStreamWriter.setDefaultNamespace(uri);
    }

    public void setNamespaceContext(NamespaceContext context) throws XMLStreamException {
        xmlStreamWriter.setNamespaceContext(context);
    }

    public NamespaceContext getNamespaceContext() {
        return xmlStreamWriter.getNamespaceContext();
    }

    public Object getProperty(String name) throws IllegalArgumentException {
        return xmlStreamWriter.getProperty(name);
    }

}

XMLStreamReaderWrapper

We need to create a wrapper for XMLStreamReader that adds everything that we stripped off on the XMLStreamWriter. This is easier to do for XMLStreamReader since we can extend StreamReaderDelegate.

package forum8198945;

import javax.xml.stream.XMLStreamReader;
import javax.xml.stream.util.StreamReaderDelegate;

public class XMLStreamReaderWrapper extends StreamReaderDelegate {

    public XMLStreamReaderWrapper(XMLStreamReader xmlStreamReader) {
        super(xmlStreamReader);
    }

    @Override
    public String getAttributeNamespace(int index) {
        String attributeName = getAttributeLocalName(index);
        if("type".equals(attributeName) || "nil".equals(attributeName)) {
            return "http://www.w3.org/2001/XMLSchema-instance";
        }
        return super.getAttributeNamespace(index);
    }


}

Demo

The following demonstrates how everything comes together:

package forum8198945;

import java.io.StringReader;
import java.io.StringWriter;
import java.util.Date;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLOutputFactory;
import javax.xml.stream.XMLStreamWriter;

public class Demo {

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

        Customer customer = new Customer();
        customer.setName("Alex Dean");
        customer.setCustomerReference(null);
        customer.setQuantity(1);
        customer.setCreatedAt(new Date());

        StringWriter stringWriter = new StringWriter();
        XMLOutputFactory xof = XMLOutputFactory.newFactory();
        XMLStreamWriter xsw = xof.createXMLStreamWriter(stringWriter);
        xsw = new XMLStreamWriterWrapper(xsw);
        Marshaller marshaller = jc.createMarshaller();
        marshaller.marshal(customer, xsw);

        String xml = stringWriter.toString();
        System.out.println(xml);

        XMLInputFactory xif = XMLInputFactory.newFactory();
        xif.createXMLStreamReader(new StringReader(xml));

        printValue(customer.getName());
        printValue(customer.getCustomerReference());
        printValue(customer.getQuantity());
        printValue(customer.getCreatedAt());
    }

    private static void printValue(Object value) {
        System.out.print(value);
        System.out.print(" ");
        if(null != value) {
            System.out.print(value.getClass());
        }
        System.out.println();
    }

}

Output

<?xml version="1.0"?><customer><createdAt type="dateTime">2011-11-25T13:36:49.095</createdAt><customerReference nil="true"></customerReference><name type="string">Alex Dean</name><quantity type="int">1</quantity></customer>
Alex Dean class java.lang.String
null 
1 class java.lang.Integer
Fri Nov 25 13:36:49 EST 2011 class java.util.Date