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:

⏎ META-INF/versions/9/javax/xml/bind/ModuleUtil.java

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright (c) 2017 Oracle and/or its affiliates. All rights reserved.
 *
 * 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:
 * "Portions Copyright [year] [name of copyright owner]"
 *
 * Contributor(s):
 * 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
 * either the CDDL, the GPL Version 2 or to extend the choice of license to
 * its licensees as provided above.  However, if you add GPL Version 2 code
 * and therefore, elected the GPL Version 2 license, then the option applies
 * only if the new code is made subject to such option by the copyright
 * holder.
 */
package javax.xml.bind;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.lang.Module;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Propagates openness of JAXB annottated classess packages to JAXB impl module.
 *
 * @author Roman Grigoriadi
 */
class ModuleUtil {

    private static Logger logger = Logger.getLogger("javax.xml.bind");

    /**
     * Resolves classes from context path.
     * Only one class per package is needed to access its {@link java.lang.Module}
     */
    static Class[] getClassesFromContextPath(String contextPath, ClassLoader classLoader) throws JAXBException {
        List<Class> classes = new ArrayList<>();
        if (contextPath == null || contextPath.isEmpty()){
          return classes.toArray(new Class[]{});
        }
        
        String [] tokens = contextPath.split(":"); 
        for (String pkg : tokens){

           // look for ObjectFactory and load it
           final Class<?> o;
           try {
               o = classLoader.loadClass(pkg+".ObjectFactory");
               classes.add(o);
               continue;
           } catch (ClassNotFoundException e) {
               // not necessarily an error
           }
              
           // look for jaxb.index and load the list of classes
           try {
               final Class firstByJaxbIndex = findFirstByJaxbIndex(pkg, classLoader);
               if (firstByJaxbIndex != null) {
                   classes.add(firstByJaxbIndex);
               }
           } catch (IOException e) {
               throw new JAXBException(e);
           }
        }

        if (logger.isLoggable(Level.FINE)) {
            logger.log(Level.FINE, "Resolved classes from context path: {0}", classes);
        }
        return classes.toArray(new Class[]{});
    }

    /**
     * Find first class in package by {@code jaxb.index} file.
     */
    static Class findFirstByJaxbIndex(String pkg, ClassLoader classLoader) throws IOException, JAXBException {
        final String resource = pkg.replace('.', '/') + "/jaxb.index";
        final InputStream resourceAsStream = classLoader.getResourceAsStream(resource);

        if (resourceAsStream == null) {
            return null;
        }

        BufferedReader in =
                new BufferedReader(new InputStreamReader(resourceAsStream, "UTF-8"));
        try {
            String className = in.readLine();
            while (className != null) {
                className = className.trim();
                if (className.startsWith("#") || (className.length() == 0)) {
                    className = in.readLine();
                    continue;
                }

                try {
                    return classLoader.loadClass(pkg + '.' + className);
                } catch (ClassNotFoundException e) {
                    throw new JAXBException(Messages.format(Messages.ERROR_LOAD_CLASS, className, pkg), e);
                }

            }
        } finally {
            in.close();
        }
        return null;
    }

    /**
     * Implementation may be defined in other module than {@code java.xml.bind}. In that case openness
     * {@linkplain Module#isOpen open} of classes should be delegated to implementation module.
     *
     * @param classes used to resolve module for {@linkplain Module#addOpens(String, Module)}
     * @param factorySPI used to resolve {@link Module} of the implementation.
     *
     * @throws JAXBException if ony of a classes package is not open to {@code java.xml.bind} module.
     */
    public static void delegateAddOpensToImplModule(Class[] classes, Class<?> factorySPI) throws JAXBException {
        final Module implModule = factorySPI.getModule();

        Module jaxbModule = JAXBContext.class.getModule();

        for (Class cls : classes) {
            Class jaxbClass = cls.isArray() ?
                cls.getComponentType() : cls;

            final Module classModule = jaxbClass.getModule();
            final String packageName = jaxbClass.getPackageName();
            //no need for unnamed and java.base types
            if (!classModule.isNamed() || classModule.getName().equals("java.base")) {
                continue;
            }
            //report error if they are not open to java.xml.bind
            if (!classModule.isOpen(packageName, jaxbModule)) {
                throw new JAXBException(Messages.format(Messages.JAXB_CLASSES_NOT_OPEN,
                                                        packageName, jaxbClass.getName(), classModule.getName()));
            }
            //propagate openness to impl module
            classModule.addOpens(packageName, implModule);
            if (logger.isLoggable(Level.FINE)) {
                logger.log(Level.FINE, "Propagating openness of package {0} in {1} to {2}.",
                           new String[]{ packageName, classModule.getName(), implModule.getName() });
            }
        }
    }

}

⏎ META-INF/versions/9/javax/xml/bind/ModuleUtil.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