jakarta.xml.bind.annotation.adapters.XmlAdapter Maven / Gradle / Ivy
/*
* 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 {@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 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 {@link
* XmlJavaTypeAdapter}
*
*
* Example: Customized mapping of {@code HashMap}
* The following example illustrates the use of
* {@code @XmlAdapter} and {@code @XmlJavaTypeAdapter} to
* customize the mapping of a {@code HashMap}.
*
*
Step 1: Determine the desired XML representation for HashMap.
*
*
{@code
*
* this is a value
* this is another value
* ...
*
* }
*
* Step 2: Determine the schema definition that the
* desired XML representation shown above should follow.
*
*
{@code
*
*
*
*
*
*
*
*
*
*
*
*
*
* }
*
* 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.
*
*
{@code
* public final class MyHashMapAdapter extends
* XmlAdapter { ... }
*
* }
*
* Step 5: Use the adapter.
*
*
* public class Foo {
* @XmlJavaTypeAdapter(MyHashMapAdapter.class)
* HashMap hashmap;
* ...
* }
*
*
* The above code fragment will map to the following schema:
*
* {@code
*
*
*
*
*
* }
*
* @param
* 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 {@code ValueType}.
* @param
* The type that JAXB knows how to handle out of the box.
*
* @author - Sekhar Vajjhala, Sun Microsystems Inc.
- Kohsuke Kawaguchi, Sun Microsystems Inc.
* @see XmlJavaTypeAdapter
* @since 1.6, JAXB 2.0
*/
public abstract class XmlAdapter {
/**
* Do-nothing constructor for the derived classes.
*/
protected XmlAdapter() {}
/**
* 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.
*
* @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;
}