Strait Fram Singapuur

Most of times we find ourself in situations where the XML instance doesn't fully comply with the available Java types.

Let's define a near real world problem to understand this.

Problem: Need to process XML message coming from some XYZ source we don't have control on( the message format is shown below). As can be seen dob element has value as date of birth for Nikhil but is surrounded by brackets [ and ]. Now if we want to unmarshal this message to Person object than with this limitation we will have to declare dob as String and then provide some more methods to parse date every time we process this XML message.

So what should we do - declare dob as String?

Nikhil
[1986-08-27]

Answer is NO, we can use adapters, how? be patient ..

Let's first define our domain object

// members are public just to keep it short..
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Person {

 @XmlElement
 public String name;

 @XmlElement
 @XmlJavaTypeAdapter(DateAdapter.class)
 public Date dob;

}

As can be seen above we have declared dob as of type Date only, but how it can be populated with the kind of values we are getting, you got it - yes it is our DateAdapter class who is going to manage this, let's see how:

/**
  * Our custom dob adapter.
  */
 class DateAdapter extends XmlAdapter<String, Date> {
  
  static SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");

  public DateAdapter() {
  }

  @Override
  public String marshal(Date date) throws Exception {
   // while sending message back to the source we will obey its format
   return "[" + format.format(date) + "]";
  }

  @Override
  public Date unmarshal(String dob) throws Exception {
   // remove unwanted characters and build date
   dob = dob.replace("[", "").replace("]", "");
   return format.parse(dob);
  }

 }

Let's unmarshal the message now:

JAXBContext context = JAXBContext.newInstance(Person.class);
  Unmarshaller unmarshal = context.createUnmarshaller();
// employee file is the source of message in this example
  Person person = (Person) unmarshal.unmarshal(new File("employee"));

  Assert.assertEquals("Nikhil", person.name);
  Assert.assertEquals("Wed Aug 27 00:00:00 SGT 1986", person.dob
    .toString());

and marshalling our new Person object works fine too :)

Person person = new Person();
  person.name="Toshi";
  person.dob= format.parse("2010-10-10");
  
  Marshaller marshaller = context.createMarshaller();
  marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
  marshaller.marshal(person, System.out);
// The console output is shown below:

  
      Toshi
      [2010-10-10]
  

This is exactly what we expect, value of dob within brackets. This was just a simple example to demonstrate the power of adapters for handling alien types in Java XML world. Hope you can also use this approach in some of your Projects.

See you later !!!