A while back a friend of mine asked for a link on how to use JAXB.  So I went to Google and attempted to find one.  After a few minutes of searching I said, “Wait a minute, it would take me like five minutes to work up a sample.” Enjoy.

JAXB is a technology to read and write XML documents, among other things.  The following tutorial uses the annotations provided by JAXB, therefore requiring Java 5 or greater.  Also, an important thing to note is that Java 6 has JAXB in the JRE distribution!  Java 5 developers just need to download the jars.

So lets get started.  Lets assume you have (or have created) the following XML document:

<?xml version="1.0" encoding="UTF-8"?>
<car>
  <feature name="leather">
    <desc>Corinthian</desc>
  </feature>
  <feature name="automatic">
    <desc>5 speed</desc>
  </feature>
</car>

The first thing to do is to create the classes necessary to represent the XML document.  In this case we will create two classes; one for each element (car and feature).

Car class:

// the tag type this class represents
// and the variable order (not necessary)
@XmlType(name = "car", propOrder = {"color", "features"})
// the tag name in the xml document
@XmlRootElement(name = "car")
public class JaxbCar {
  // any simple type, String, primitives
  @XmlElement(required = false)
  // the variable, uses "color" as the name to
  // look for in the xml document
  private String color;
  // list of stuff, the name in the xml document
  @XmlElement(required = false, name = "feature")
  // the variable
  private List<JaxbFeature> features = new arrayList<JaxbFeature>();
  // getter/setters
}

Feature class:

@XmlType(name = "feature", propOrder = {"name", "description"})
@XmlRootElement(name = "feature")
public class JaxbFeature {
  // defines an attribute instead of an element
  @XmlAttribute(required = false)
  private String name;
  @XmlElement(required = false, name = "desc")
  private String description;
  // getter/setters
}

Next, we need to create an XML registry, which will be used by the Unmarshaller to create the classes when reading the XML document.

ObjectFactory class:

@XmlRegistry
public class ObjectFactory {
  // there has to be a method for each
  // element in the xml document
  public JaxbCar createCar() {
    return new JaxbCar();
  }
  public JaxbFeature createFeature() {
    return new JaxbFeature();
  }
}

I can’t remember if the name of the registry has to be ObjectFactory.  I don’t think it does (in which case you have to configure it somewhere), but I haven’t had time to research it.

Next we have the definition of the schema which is done on the package-info.java file in the same package as the above classes.

package-info.java file:

@javax.xml.bind.annotation.XmlSchema(namespace="", elementFormDefault=javax.xml.bind.annotation.XmlNsForm.QUALIFIED)
@javax.xml.bind.annotation.XmlAccessorType(value=javax.xml.bind.annotation.XmlAccessType.NONE)
package thep.ackage.containing.the.above.classes;

Once the above is created we can unmarshall (read) and marshall (write) our XML document.

Sample method:

// create the Jaxb context
JAXBContext context = JAXBContext.newInstance("thep.ackage.containing.the.above.classes");
// create an unmarshaller
Unmarshaller unmarshaller = context.createUnmarshaller();
// use a marshaller to write xml
try {
  // use the unmarshaller to translate an inputstream
  JaxbCar car = (JaxbCar) unmarshaller.unmarshal(inputstream);
} catch ( MalformedURLException e ) {
} catch ( ProtocolException e ) {
} catch ( IOException e ) {
}