Adapts a Java type for custom marshaling.
Usage:
Some Java types do not map naturally to an XML representation, for
example
HashMap or other non JavaBean classes. Conversely,
an XML representation may map to a Java type but an application may
choose to access the XML representation using another Java
type. For example, the schema to Java binding rules bind
xs:DateTime by default to XmlGregorianCalendar. But an application
may desire to bind xs:DateTime to a custom type,
MyXmlGregorianCalendar, for example. In both cases, there is a
mismatch between bound type , used by an application to
access XML content and the value type, that is mapped to an
XML representation.
This abstract class defines methods for adapting a bound type to a value
type or vice versa. The methods are invoked by the JAXB binding
framework during marshaling and unmarshalling:
- XmlAdapter.marshal(...): During marshalling, JAXB
binding framework invokes XmlAdapter.marshal(..) to adapt a
bound type to value type, which is then marshaled to XML
representation.
- XmlAdapter.unmarshal(...): During unmarshalling,
JAXB binding framework first unmarshals XML representation
to a value type and then invokes XmlAdapter.unmarshal(..) to
adapt the value type to a bound type.
Writing an adapter therefore involves the following steps:
- Write an adapter that implements this abstract class.
- Install the adapter using the annotation
XmlJavaTypeAdapter
Example: Customized mapping of
HashMap
The following example illustrates the use of
@XmlAdapter and
@XmlJavaTypeAdapter to
customize the mapping of a
HashMap.
Step 1: Determine the desired XML representation for HashMap.
Step 2: Determine the schema definition that the
desired XML representation shown above should follow.
Step 3: Write value types that can generate the above
schema definition.
public class MyHashMapType {
List<MyHashMapEntryType> entry;
}
public class MyHashMapEntryType {
@XmlAttribute
public Integer key;
@XmlValue
public String value;
}
Step 4: Write the adapter that adapts the value type,
MyHashMapType to a bound type, HashMap, used by the application.
public final class MyHashMapAdapter extendsXmlAdapter { ... }
}
Step 5: Use the adapter.
public class Foo {
@XmlJavaTypeAdapter(MyHashMapAdapter.class)
HashMap hashmap;
...
}
The above code fragment will map to the following schema: