Case Insensitive Unmarshalling with JAXB

Recently I've been asked in a couple different forums how to handle case insensitive unmarshalling in JAXB.  In this post I'll discuss an approach using a StAX StreamReaderDelegate.

I am considering adding this as an official feature, and would be interested in your feed back.  I am using the following bug to track this issue:

• https://bugs.eclipse.org/331241

XML Inputs

We want our JAXB implementation to be able to unmarshal the following XML documents to the same object model:

<customer id="1">
    <name>Jane Doe</name>
    <address>
        <street>123 A Street</street>
    </address>
</customer>

<CUSTOMER ID="1">
    <NAME>Jane Doe</NAME>
    <ADDRESS>
        <STREET>123 A Street</STREET>
    </ADDRESS>
</CUSTOMER>

<CuStOMeR Id="1">
    <NaMe>Jane Doe</NaMe>
    <AdDrEsS>
        <StReEt>123 A Street</StReEt>
    </AdDrEsS>
</CuStOMeR>

Java Model

In the object model we will ensure that all the resulting node names are lower case.  For this object model the default mappings give us this behavior.  For other object models we could leverage the @XmlElement and @XmlAttribute annotations to achieve this:

package blog.caseinsensitive;

import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class Customer {

    private int id;
    private String name;
    private Address address;

    @XmlAttribute
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public Address getAddress() {
        return address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

}

package blog.caseinsensitive;

public class Address {

    private String street;

    public String getStreet() {
        return street;
    }

    public void setStreet(String street) {
        this.street = street;
    }

}

Demo Code

We will achieve the desired effect by filtering the XML input.  This will be done by using a StreamReaderDelegate.  This delegate lets us filter the output from an XMLStreamReader.  We will leverage this delegate to return all element and attribute names as lower case.

package blog.caseinsensitive;

import java.io.FileInputStream;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamReader;
import javax.xml.stream.util.StreamReaderDelegate;

public class Demo {

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

        XMLInputFactory xif = XMLInputFactory.newInstance();
        XMLStreamReader xsr = xif.createXMLStreamReader(new FileInputStream("src/blog/caseinsensitive/input2.xml"));
        xsr = new MyStreamReaderDelegate(xsr);

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

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

    private static class MyStreamReaderDelegate extends StreamReaderDelegate {

        public MyStreamReaderDelegate(XMLStreamReader xsr) {
            super(xsr);
        }

        @Override
        public String getAttributeLocalName(int index) {
            return super.getAttributeLocalName(index).toLowerCase();
        }

        @Override
        public String getLocalName() {
            return super.getLocalName().toLowerCase();
        }

    }

}

XML Output

The following is the resulting XML, the output will match the provided JAXB mappings:

<customer id="1">
    <name>Jane Doe</name>
    <address>
        <street>123 A Street</street>
    </address>
</customer>