JAXB in 3 minutes

JAXB is a handy technology that easily transforms Java objects to XML documents and vice versa.

Define the object

There is a business need to define and use messages. For every message we need:

• The sender
• The receiver
• The actual message
• A unique identification

@XmlRootElement
public class Message {
   private String from;
   private String to;
   private String text;
   private int id;
}

API: XmlRootElement

We would like the id to be an attribute of the root element.

@XmlRootElement
public class Message {
   private String from;
   private String to;
   private String text;
   private int id;

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

API: XmlAttribute

Here’s the complete class.

/**
 * A message.
 */
@XmlRootElement
public class Message {
   /**
    * The sender.
    */
   private String from;
   /**
    * The receiver.
    */
   private String to;
   /**
    * A unique identification.
    */
   private int id;
   /**
    * The actual message.
    */
   private String text;
   /**
    * Default contstructor.
    */
   public Message() {
   }
   public String getFrom() {
      return from;
   }
   public void setFrom(String from) {
      this.from = from;
   }
   public String getTo() {
      return to;
   }
   public void setTo(String to) {
      this.to = to;
   }
   public String getText() {
      return text;
   }
   public void setText(String text) {
      this.text = text;
   }
   public int getId() {
      return id;
   }
   @XmlAttribute
   public void setId(int id) {
      this.id = id;
   }
   public String toString() {
      return String.format("Message[id=%s, from=%s, to=%s, text=%s]", id, from, to, text);
   }
}

Write the object to XML

In order to write/serialize/marshal the Java object to XML follow these simple steps.

Message message = new Message();
message.setFrom("Nikos");
message.setTo("Sofia");
message.setText("Hello from JAXB!");
message.setId(123);

// Create a JAXB context and a marshaller
JAXBContext context = JAXBContext.newInstance(Message.class);
Marshaller handler = context.createMarshaller();
// Set the output in pretty format
handler.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
// Make the actual serialization
handler.marshal(message, new File("/output.xml"));

API: JAXBContext, Marshaller

Get the object from XML

It is equally easy to read/deserialize/unmarshal the Java object from its XML representation.

// Create a JAXB context and an unmarshaller
JAXBContext context = JAXBContext.newInstance(Message.class);
Unmarshaller handler = context.createUnmarshaller();
// Get the object
Message msg = (Message)handler.unmarshal(new File("/output.xml"));

API: Unmarshaller

Summary

The output should be

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<message id="123">
   <from>Nikos</from>
   <text>Hello from JAXB!</text>
   <to>Sofia</to>
</message>

Java Architecture for XML-Binding is part of core Java since Standard Edition 6. Moreover, it is a basic component of Java Web Services.

• API
• Reference Implementation
• Using JAXB, from the The Java Web Services Tutorial

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