- Roman Grigoriadi (Oracle Corporation)
/*
* Copyright (c) 2004, 2020 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Distribution License v. 1.0, which is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
package jakarta.xml.bind.annotation.adapters;
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 Jakarta XML Binding binding
framework during marshaling and unmarshalling:
- XmlAdapter.marshal(...): During marshalling, Jakarta XML Binding
binding framework invokes XmlAdapter.marshal(..) to adapt a
bound type to value type, which is then marshaled to XML
representation.
- XmlAdapter.unmarshal(...): During unmarshalling,
Jakarta XML Binding 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>
Author: - Sekhar Vajjhala, Sun Microsystems Inc.
- Kohsuke Kawaguchi, Sun Microsystems Inc.
Type parameters: See Also: Since: 1.6, JAXB 2.0
/**
* Adapts a Java type for custom marshaling.
*
* <p> <b> Usage: </b> </p>
*
* <p>
* Some Java types do not map naturally to an XML representation, for
* example {@code 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 <i> bound type </i>, used by an application to
* access XML content and the <i> value type</i>, that is mapped to an
* XML representation.
*
* <p>
* This abstract class defines methods for adapting a bound type to a value
* type or vice versa. The methods are invoked by the Jakarta XML Binding binding
* framework during marshaling and unmarshalling:
*
* <ul>
* <li> <b> XmlAdapter.marshal(...): </b> During marshalling, Jakarta XML Binding
* binding framework invokes XmlAdapter.marshal(..) to adapt a
* bound type to value type, which is then marshaled to XML
* representation. </li>
*
* <li> <b> XmlAdapter.unmarshal(...): </b> During unmarshalling,
* Jakarta XML Binding binding framework first unmarshals XML representation
* to a value type and then invokes XmlAdapter.unmarshal(..) to
* adapt the value type to a bound type. </li>
* </ul>
*
* Writing an adapter therefore involves the following steps:
*
* <ul>
* <li> Write an adapter that implements this abstract class. </li>
* <li> Install the adapter using the annotation {@link
* XmlJavaTypeAdapter} </li>
* </ul>
*
* <p><b>Example:</b> Customized mapping of {@code HashMap}</p>
* <p> The following example illustrates the use of
* {@code @XmlAdapter} and {@code @XmlJavaTypeAdapter} to
* customize the mapping of a {@code HashMap}.
*
* <p> <b> Step 1: </b> Determine the desired XML representation for HashMap.
*
* <pre>{@code
* <hashmap>
* <entry key="id123">this is a value</entry>
* <entry key="id312">this is another value</entry>
* ...
* </hashmap>
* }</pre>
*
* <p> <b> Step 2: </b> Determine the schema definition that the
* desired XML representation shown above should follow.
*
* <pre>{@code
*
* <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>
*
* }</pre>
*
* <p> <b> Step 3: </b> Write value types that can generate the above
* schema definition.
*
* <pre>
* public class MyHashMapType {
* List<MyHashMapEntryType> entry;
* }
*
* public class MyHashMapEntryType {
* @XmlAttribute
* public Integer key;
*
* @XmlValue
* public String value;
* }
* </pre>
*
* <p> <b> Step 4: </b> Write the adapter that adapts the value type,
* MyHashMapType to a bound type, HashMap, used by the application.
*
* <pre>{@code
* public final class MyHashMapAdapter extends
* XmlAdapter<MyHashMapType,HashMap> { ... }
*
* }</pre>
*
* <p> <b> Step 5: </b> Use the adapter.
*
* <pre>
* public class Foo {
* @XmlJavaTypeAdapter(MyHashMapAdapter.class)
* HashMap hashmap;
* ...
* }
* </pre>
*
* The above code fragment will map to the following schema:
*
* <pre>{@code
* <xs:complexType name="Foo">
* <xs:sequence>
* <xs:element name="hashmap" type="myHashMapType">
* </xs:sequence>
* </xs:complexType>
* }</pre>
*
* @param <BoundType>
* The type that Jakarta XML Binding doesn't know how to handle. An adapter is written
* to allow this type to be used as an in-memory representation through
* the {@code ValueType}.
* @param <ValueType>
* The type that Jakarta XML Binding knows how to handle out of the box.
*
* @author <ul><li>Sekhar Vajjhala, Sun Microsystems Inc.</li> <li> Kohsuke Kawaguchi, Sun Microsystems Inc.</li></ul>
* @see XmlJavaTypeAdapter
* @since 1.6, JAXB 2.0
*/
public abstract class XmlAdapter<ValueType,BoundType> {
Do-nothing constructor for the derived classes.
/**
* Do-nothing constructor for the derived classes.
*/
protected XmlAdapter() {}
Convert a value type to a bound type.
Params: - 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 through
ValidationEventHandler.
/**
* Convert a value type to a bound type.
*
* @param 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 through {@link jakarta.xml.bind.ValidationEventHandler}.
*/
public abstract BoundType unmarshal(ValueType v) throws Exception;
Convert a bound type to a value type.
Params: - 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 through
ValidationEventHandler.
/**
* Convert a bound type to a value type.
*
* @param 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 through {@link jakarta.xml.bind.ValidationEventHandler}.
*/
public abstract ValueType marshal(BoundType v) throws Exception;
}