Class 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 Object
    Adapts a Java type for custom marshaling.


    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.

             <entry key="id123">this is a value</entry>
             <entry key="id312">this is another value</entry>

    Step 2: Determine the schema definition that the desired XML representation shown above should follow.

         <xs:complexType name="myHashMapType">
             <xs:element name="entry" type="myHashMapEntryType"
                            minOccurs = "0" maxOccurs="unbounded"/>
         <xs:complexType name="myHashMapEntryType">
             <xs:extension base="xs:string">
               <xs:attribute name="key" type="xs:int"/>

    Step 3: Write value types that can generate the above schema definition.

         public class MyHashMapType {
             List<MyHashMapEntryType> entry;
         public class MyHashMapEntryType {
             public Integer key;
             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 {
             HashMap hashmap;
    The above code fragment will map to the following schema:
         <xs:complexType name="Foo">
             <xs:element name="hashmap" type="myHashMapType">
    1.6, JAXB 2.0
    See Also:
    • Constructor Detail

      • XmlAdapter

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

      • unmarshal

        public abstract BoundType unmarshal​(ValueType v)
                                     throws Exception
        Convert a value type to a bound type.
        v - The value to be converted. Can be null.
        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 Exception
        Convert a bound type to a value type.
        v - The value to be convereted. Can be null.
        Exception - if there's an error during the conversion. The caller is responsible for reporting the error to the user through ValidationEventHandler.