| Adapts a Java type for custom marshaling.
Usage:
Some Java types do not map naturally to a XML representation, for
example HashMap or other non JavaBean classes. Conversely,
a XML repsentation may map to a Java type but an application may
choose to accesss 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.
<hashmap>
<entry key="id123">this is a value</entry>
<entry key="id312">this is another value</entry>
...
</hashmap>
Step 2: Determine the schema definition that the
desired XML representation shown above should follow.
<xs:complexType name="myHashMapType">
<xs:sequence>
<xs:element name="entry" type="myHashMapEntryType"
minOccurs = "0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="myHashMapEntryType">
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="key" type="xs:int"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
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 extends
XmlAdapter<HashMap, MyHashMapType> { ... }
Step 5: Use the adapter.
public class Foo {
@XmlJavaTypeAdapter(MyHashMapAdapter.class)
HashMap hashmap;
...
}
The above code fragment will map to the following schema:
<xs:complexType name="Foo">
<xs:sequence>
<xs:element name="hashmap" type="myHashMapType"
</xs:sequence>
</xs:complexType>
<
Parameters:
BoundType - >The type that JAXB doesn't know how to handle. An adapter is writtento allow this type to be used as an in-memory representation throughthe ValueType.<
Parameters:
ValueType - >The type that JAXB knows how to handle out of the box.
author:
- Sekhar Vajjhala, Sun Microsystems Inc.
- Kohsuke Kawaguchi, Sun Microsystems Inc.
See Also: XmlJavaTypeAdapter
since:
JAXB 2.0 | 