- java.lang.Object
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- javax.xml.bind.annotation.adapters.XmlAdapter<ValueType,BoundType>
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- 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.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.
- 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
- See Also:
XmlJavaTypeAdapter
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Constructor Summary
Constructors Modifier Constructor and Description protected
XmlAdapter()
Do-nothing constructor for the derived classes.
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Constructor Detail
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XmlAdapter
protected XmlAdapter()
Do-nothing constructor for the derived classes.
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Method Detail
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unmarshal
public abstract BoundType unmarshal(ValueType v) throws Exception
Convert a value type to a bound type.- Parameters:
v
- The value to be converted. Can be null.- Throws:
Exception
- if there's an error during the conversion. The caller is responsible for reporting the error to the user throughValidationEventHandler
.
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marshal
public abstract ValueType marshal(BoundType v) throws Exception
Convert a bound type to a value type.- Parameters:
v
- The value to be convereted. Can be null.- Throws:
Exception
- if there's an error during the conversion. The caller is responsible for reporting the error to the user throughValidationEventHandler
.
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