Java Architecture for XML Binding (JAXB) is a Java API that allows Java developers to map Java classes to XML representations.

jaxb-api-2.3.1.jar is the JAR file for the JAXB API 2.3 specification. You can download and use it directly without any building process as shown in the last tutorial.

If you want to rebuild the JAR file, you can download the source code at JAXB API Maven Website.

You can also browse the source code below:

⏎ javax/xml/bind/annotation/XmlElementWrapper.java

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 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * https://oss.oracle.com/licenses/CDDL+GPL-1.1
 * or LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at LICENSE.txt.
 *
 * GPL Classpath Exception:
 * Oracle designates this particular file as subject to the "Classpath"
 * exception as provided by Oracle in the GPL Version 2 section of the License
 * file that accompanied this code.
 *
 * Modifications:
 * If applicable, add the following below the License Header, with the fields
 * enclosed by brackets [] replaced by your own identifying information:
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 * If you wish your version of this file to be governed by only the CDDL or
 * only the GPL Version 2, indicate your decision by adding "[Contributor]
 * elects to include this software in this distribution under the [CDDL or GPL
 * Version 2] license."  If you don't indicate a single choice of license, a
 * recipient has the option to distribute your version of this file under
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 */

package javax.xml.bind.annotation;

import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * Generates a wrapper element around XML representation.
 *
 * This is primarily intended to be used to produce a wrapper
 * XML element around collections. The annotation therefore supports
 * two forms of serialization shown below. 
 *
 * <pre>{@code
 *    //Example: code fragment
 *      int[] names;
 *
 *    // XML Serialization Form 1 (Unwrapped collection)
 *    <names> ... </names>
 *    <names> ... </names>
 * 
 *    // XML Serialization Form 2 ( Wrapped collection )
 *    <wrapperElement>
 *       <names> value-of-item </names>
 *       <names> value-of-item </names>
 *       ....
 *    </wrapperElement>
 * }</pre>
 *
 * <p> The two serialized XML forms allow a null collection to be
 * represented either by absence or presence of an element with a
 * nillable attribute.
 * 
 * <p> <b>Usage</b> </p>
 * <p>
 * The {@code @XmlElementWrapper} annotation can be used with the
 * following program elements: 
 * <ul> 
 *   <li> JavaBean property </li>
 *   <li> non static, non transient field </li>
 * </ul>
 *
 * <p>The usage is subject to the following constraints:
 * <ul>
 *   <li> The property must be a collection property </li>
 *   <li> This annotation can be used with the following annotations:
 *            {@link XmlElement}, 
 *            {@link XmlElements},
 *            {@link XmlElementRef},
 *            {@link XmlElementRefs},
 *            {@link XmlJavaTypeAdapter}.</li>
 * </ul>
 *
 * <p>See "Package Specification" in javax.xml.bind.package javadoc for
 * additional common information.</p>
 *
 * @author <ul><li>Kohsuke Kawaguchi, Sun Microsystems, Inc.</li><li>Sekhar Vajjhala, Sun Microsystems, Inc.</li></ul>
 * @see XmlElement 
 * @see XmlElements
 * @see XmlElementRef
 * @see XmlElementRefs
 * @since 1.6, JAXB 2.0
 *
 */

@Retention(RUNTIME) @Target({FIELD, METHOD})
public @interface XmlElementWrapper {
    /**
     * Name of the XML wrapper element. By default, the XML wrapper
     * element name is derived from the JavaBean property name.
     */
    String name() default "##default";

    /**
     * XML target namespace of the XML wrapper element.
     * <p>
     * If the value is "##default", then the namespace is determined
     * as follows:
     * <ol>
     *  <li>
     *  If the enclosing package has {@link XmlSchema} annotation,
     *  and its {@link XmlSchema#elementFormDefault() elementFormDefault}
     *  is {@link XmlNsForm#QUALIFIED QUALIFIED}, then the namespace of
     *  the enclosing class.
     *
     *  <li>
     *  Otherwise "" (which produces unqualified element in the default
     *  namespace.
     * </ol>
     */
    String namespace() default "##default";

    /**
     * If true, the absence of the collection is represented by
     * using {@code xsi:nil='true'}. Otherwise, it is represented by
     * the absence of the element.
     */
    boolean nillable() default false;

    /**
     * Customize the wrapper element declaration to be required.
     *
     * <p>
     * If required() is true, then the corresponding generated
     * XML schema element declaration will have {@code minOccurs="1"},
     * to indicate that the wrapper element is always expected.
     *
     * <p>
     * Note that this only affects the schema generation, and
     * not the unmarshalling or marshalling capability. This is
     * simply a mechanism to let users express their application constraints
     * better.
     *
     * @since 1.6, JAXB 2.1
     */
    boolean required() default false;
}

⏎ javax/xml/bind/annotation/XmlElementWrapper.java

Or download all of them as a single archive file:

File name: jaxb-api-2.3.1-sources.jar
File size: 271123 bytes
Release date: 2018-10-10
Download 

⇒ Download JAXB 2.2 Specification and API JAR

⇐ Download JAXB 2.3 Specification and API JAR

⇑ JAXB (Java Architecture for XML Binding) API Specification

⇑⇑ FAQ for jaxb-*.jar - Java Architecture for XML Binding