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Java Enterprise Edition (EE)

XmlAdapter


javax.xml.bind.annotation.adapters
Class XmlAdapter<ValueType,BoundType>

java.lang.Object
  javax.xml.bind.annotation.adapters.XmlAdapter<ValueType,BoundType>
Type Parameters:
BoundType - The type that JAXB doesn't know how to handle. An adapter is written to allow this type to be used as an in-memory representation through the ValueType.
ValueType - The type that JAXB knows how to handle out of the box.
Direct Known Subclasses:
CollapsedStringAdapter, HexBinaryAdapter, NormalizedStringAdapter
public abstract class XmlAdapter<ValueType,BoundType>
extends java.lang.Object

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<MyHashMapType,HashMap> { ... }
      
 

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>
 

Since:
JAXB 2.0
Author:
  • Sekhar Vajjhala, Sun Microsystems Inc.
  • Kohsuke Kawaguchi, Sun Microsystems Inc.
See Also:
XmlJavaTypeAdapter

Constructor Summary
protected XmlAdapter()
          Do-nothing constructor for the derived classes.
 
Method Summary
abstract  ValueType marshal(BoundType v)
          Convert a bound type to a value type.
abstract  BoundType unmarshal(ValueType v)
          Convert a value type to a bound type.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

XmlAdapter

protected XmlAdapter()
Do-nothing constructor for the derived classes.

Method Detail

unmarshal

public abstract BoundType unmarshal(ValueType v)
                             throws java.lang.Exception
Convert a value type to a bound type.

Parameters:
v - The value to be converted. Can be null.
Throws:
java.lang.Exception - if there's an error during the conversion. The caller is responsible for reporting the error to the user through ValidationEventHandler.

marshal

public abstract ValueType marshal(BoundType v)
                           throws java.lang.Exception
Convert a bound type to a value type.

Parameters:
v - The value to be convereted. Can be null.
Throws:
java.lang.Exception - if there's an error during the conversion. The caller is responsible for reporting the error to the user through ValidationEventHandler.


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