package org.codehaus.mojo.jaxb2.schemageneration;
   
   /*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
   * with the License.  You may obtain a copy of the License at
   *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing,
   * software distributed under the License is distributed on an
   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   * KIND, either express or implied.  See the License for the
   * specific language governing permissions and limitations
   * under the License.
   */
  
  import com.sun.tools.jxc.SchemaGenerator;
  import com.thoughtworks.qdox.JavaProjectBuilder;
  import com.thoughtworks.qdox.model.JavaClass;
  import com.thoughtworks.qdox.model.JavaPackage;
  import com.thoughtworks.qdox.model.JavaSource;
  import org.apache.maven.plugin.MojoExecutionException;
  import org.apache.maven.plugin.MojoFailureException;
  import org.apache.maven.plugins.annotations.Parameter;
  import org.codehaus.mojo.jaxb2.AbstractJaxbMojo;
  import org.codehaus.mojo.jaxb2.schemageneration.postprocessing.javadoc.DefaultJavaDocRenderer;
  import org.codehaus.mojo.jaxb2.schemageneration.postprocessing.javadoc.JavaDocExtractor;
  import org.codehaus.mojo.jaxb2.schemageneration.postprocessing.javadoc.JavaDocRenderer;
  import org.codehaus.mojo.jaxb2.schemageneration.postprocessing.javadoc.SearchableDocumentation;
  import org.codehaus.mojo.jaxb2.schemageneration.postprocessing.schemaenhancement.SimpleNamespaceResolver;
  import org.codehaus.mojo.jaxb2.schemageneration.postprocessing.schemaenhancement.TransformSchema;
  import org.codehaus.mojo.jaxb2.shared.FileSystemUtilities;
  import org.codehaus.mojo.jaxb2.shared.arguments.ArgumentBuilder;
  import org.codehaus.mojo.jaxb2.shared.environment.EnvironmentFacet;
  import org.codehaus.mojo.jaxb2.shared.environment.ToolExecutionEnvironment;
  import org.codehaus.mojo.jaxb2.shared.environment.classloading.ThreadContextClassLoaderBuilder;
  import org.codehaus.mojo.jaxb2.shared.environment.locale.LocaleFacet;
  import org.codehaus.mojo.jaxb2.shared.environment.logging.LoggingHandlerEnvironmentFacet;
  import org.codehaus.mojo.jaxb2.shared.filters.Filter;
  import org.codehaus.mojo.jaxb2.shared.filters.pattern.PatternFileFilter;
  import org.codehaus.plexus.classworlds.realm.ClassRealm;
  import org.codehaus.plexus.util.FileUtils;
  
  import javax.tools.ToolProvider;
  import java.io.File;
  import java.io.IOException;
  import java.net.HttpURLConnection;
  import java.net.URL;
  import java.net.URLConnection;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.List;
  import java.util.Map;
  import java.util.SortedMap;
  import java.util.TreeMap;
  import java.util.regex.Pattern;
  
  /**
   * <p>Abstract superclass for Mojos that generate XSD files from annotated Java Sources.
   * This Mojo delegates execution to the {@code schemagen} tool to perform the XSD file
   * generation. Moreover, the AbstractXsdGeneratorMojo provides an augmented processing
   * pipeline by optionally letting a set of NodeProcessors improve the 'vanilla' XSD files.</p>
   *
   * @author <a href="mailto:lj@jguru.se">Lennart J&ouml;relid</a>
   * @see <a href="https://jaxb.java.net/">The JAXB Reference Implementation</a>
   */
  public abstract class AbstractXsdGeneratorMojo extends AbstractJaxbMojo {
  
      /**
       * <p>Pattern matching the names of files emitted by the JAXB/JDK SchemaGenerator.
       * According to the JAXB Schema Generator documentation:</p>
       * <blockquote>There is no way to control the name of the generated schema files at this time.</blockquote>
       */
      public static final Pattern SCHEMAGEN_EMITTED_FILENAME = Pattern.compile("schema\\p{javaDigit}+.xsd");
  
      /**
       * <p>The default JavaDocRenderer used unless another JavaDocRenderer should be used.</p>
       *
       * @see #javaDocRenderer
       * @since 2.0
       */
      public static final JavaDocRenderer STANDARD_JAVADOC_RENDERER = new DefaultJavaDocRenderer();
  
      /**
       * <p>Default exclude file name suffixes for testSources, used unless overridden by an
       * explicit configuration in the {@code testSourceExcludeSuffixes} parameter.
       * </p>
       * <pre>
       *     <code>
       *         final List&lt;Filter&lt;File&gt;&gt; schemagenTmp = new ArrayList&lt;Filter&lt;File&gt;&gt;();
       *         schemagenTmp.addAll(AbstractJaxbMojo.STANDARD_EXCLUDE_FILTERS);
       *         schemagenTmp.add(new PatternFileFilter(Arrays.asList("\\.java", "\\.scala", "\\.mdo"), false));
      *         STANDARD_BYTECODE_EXCLUDE_FILTERS = Collections.unmodifiableList(schemagenTmp);
      *     </code>
      * </pre>
      */
     public static final List<Filter<File>> STANDARD_BYTECODE_EXCLUDE_FILTERS;
 
     /**
      * Filter list containing a PatternFileFilter including ".class" files.
      */
     public static final List<Filter<File>> CLASS_INCLUDE_FILTERS;
 
     /**
      * Specification for packages which must be loaded using the SystemToolClassLoader (and not in the plugin's
      * ThreadContext ClassLoader). The SystemToolClassLoader is used by SchemaGen to process some stuff from the
      * {@code tools.jar} archive, in particular its exception types used to signal JAXB annotation Exceptions.
      *
      * @see ToolProvider#getSystemToolClassLoader()
      */
     public static final List<String> SYSTEM_TOOLS_CLASSLOADER_PACKAGES = Arrays.asList(
             "com.sun.source.util",
             "com.sun.source.tree");
 
     static {
 
         final List<Filter<File>> schemagenTmp = new ArrayList<Filter<File>>();
         schemagenTmp.addAll(AbstractJaxbMojo.STANDARD_EXCLUDE_FILTERS);
         schemagenTmp.add(new PatternFileFilter(Arrays.asList("\\.java", "\\.scala", "\\.mdo"), false));
         STANDARD_BYTECODE_EXCLUDE_FILTERS = Collections.unmodifiableList(schemagenTmp);
 
         CLASS_INCLUDE_FILTERS = new ArrayList<Filter<File>>();
         CLASS_INCLUDE_FILTERS.add(new PatternFileFilter(Arrays.asList("\\.class"), true));
     }
 
     // Internal state
     private static final int SCHEMAGEN_INCORRECT_OPTIONS = -1;
     private static final int SCHEMAGEN_COMPLETED_OK = 0;
     private static final int SCHEMAGEN_JAXB_ERRORS = 1;
 
     /**
      * <p>A List holding desired schema mappings, each of which binds a schema namespace URI to its desired prefix
      * [optional] and the name of the resulting schema file [optional]. All given elements (uri, prefix, file) must be
      * unique within the configuration; no two elements may have the same values.</p>
      * <p>The example schema configuration below maps two namespace uris to prefixes and generated file names. This implies
      * that <tt>http://some/namespace</tt> will be represented by the prefix <tt>some</tt> within the generated XML
      * Schema files; creating namespace definitions on the form <tt>xmlns:some="http://some/namespace"</tt>, and
      * corresponding uses on the form <tt>&lt;xs:element minOccurs="0"
      * ref="<strong>some:</strong>anOptionalElementInSomeNamespace"/></tt>. Moreover, the file element defines that the
      * <tt>http://some/namespace</tt> definitions will be written to the file <tt>some_schema.xsd</tt>, and that all
      * import references will be on the form <tt>&lt;xs:import namespace="http://some/namespace"
      * schemaLocation="<strong>some_schema.xsd</strong>"/></tt></p>
      * <p>The example configuration below also performs identical operations for the namespace uri
      * <tt>http://another/namespace</tt> with the prefix <tt>another</tt> and the file <tt>another_schema.xsd</tt>.
      * </p>
      * <pre>
      *     <code>
      * &lt;transformSchemas>
      *   &lt;transformSchema>
      *     &lt;uri>http://some/namespace&lt;/uri>
      *     &lt;toPrefix>some&lt;/toPrefix>
      *     &lt;toFile>some_schema.xsd&lt;/toFile>
      *   &lt;transformSchema>
      *     &lt;uri>http://another/namespace&lt;/uri>
      *     &lt;toPrefix>another&lt;/toPrefix>
      *     &lt;toFile>another_schema.xsd&lt;/toFile>
      *   &lt;/transformSchema>
      * &lt;/transformSchemas>
      *     </code>
      * </pre>
      *
      * @since 1.4
      */
     @Parameter
     private List<TransformSchema> transformSchemas;
 
     /**
      * <strong>Deprecated - will be removed in a future release</strong>
      * <p>From plugin version 2.4, this parameter will not be used.
      * Instead, episode files are generated by default with all JAXB operations.</p>
      * <p>Starting with plugin version 2.4, use the parameter {@link #episodeFileName} to provide a custom
      * name of the generated episode File (or rely on the standard file name {@link #STANDARD_EPISODE_FILENAME}).</p>
      *
      * @since 2.0
      * @deprecated
      */
     @Deprecated
     @Parameter(defaultValue = "true")
     protected boolean generateEpisode;
 
     /**
      * <p>Corresponding SchemaGen parameter: {@code episode}.</p>
      * <p>Generate an episode file with the supplied name from this XSD generation, so that other schemas that rely
      * on this schema can be compiled later and rely on classes that are generated from this compilation.
      * The generated episode file is simply a JAXB customization file (but with vendor extensions), normally known
      * as a <em>binding file</em> with the suffix <code>.xjb</code>.</p>
      * <p>If the <code>episodeFileName</code> parameter is not given, the episode file name is synthesized on the form
      * <code>"episode_" + executionID + ".xjb"</code> - typically something like <em>episode_schemagen.xjb</em>, but
      * it depends on the actual ID given in the execution element:</p>
      * <pre>
      *     <code>
      * &lt;executions&gt;
      *     &lt;execution&gt;
      *         &lt;id&gt;schemagen&lt;/id&gt;
      *         &lt;goals&gt;
      *             &lt;goal&gt;schemagen&lt;/goal&gt;
      *         &lt;/goals&gt;
      *     &lt;/execution&gt;
      * &lt;/executions&gt;
      *      </code>
      * </pre>
      *
      * @see #STANDARD_EPISODE_FILENAME
      * @since 2.4
      */
     @Parameter
     protected String episodeFileName;
 
     /**
      * <p>If {@code true}, Elements or Attributes in the generated XSD files will be annotated with any
      * JavaDoc found for their respective properties. If {@code false}, no XML documentation annotations will be
      * generated in post-processing any results from the JAXB SchemaGenerator.</p>
      *
      * @since 2.0
      */
     @Parameter(defaultValue = "true")
     protected boolean createJavaDocAnnotations;
 
     /**
      * <p>A renderer used to create XML annotation text from JavaDoc comments found within the source code.
      * Unless another implementation is provided, the standard JavaDocRenderer used is
      * {@linkplain org.codehaus.mojo.jaxb2.schemageneration.postprocessing.javadoc.DefaultJavaDocRenderer}.</p>
      *
      * @see org.codehaus.mojo.jaxb2.schemageneration.postprocessing.javadoc.DefaultJavaDocRenderer
      * @since 2.0
      */
     @Parameter
     protected JavaDocRenderer javaDocRenderer;
 
     /**
      * <p>Removes all files from the output directory before running SchemaGenerator.</p>
      *
      * @since 2.0
      */
     @Parameter(defaultValue = "true")
     protected boolean clearOutputDir;
 
     /**
      * <p>XSD schema files are not generated from POM projects or if no includes have been supplied.</p>
      * {@inheritDoc}
      */
     @Override
     protected boolean shouldExecutionBeSkipped() {
 
         boolean toReturn = false;
 
         if ("pom".equalsIgnoreCase(getProject().getPackaging())) {
             warnAboutIncorrectPluginConfiguration("packaging", "POM-packaged projects should not generate XSDs.");
             toReturn = true;
         }
 
         if (getSources().isEmpty()) {
             warnAboutIncorrectPluginConfiguration("sources", "At least one Java Source file has to be included.");
             toReturn = true;
         }
 
         // All done.
         return toReturn;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     protected boolean isReGenerationRequired() {
 
         //
         // Use the stale flag method to identify if we should re-generate the XSDs from the sources.
         // Basically, we should re-generate the XSDs if:
         //
         // a) The staleFile does not exist
         // b) The staleFile exists and is older than one of the sources (Java or XJB files).
         //    "Older" is determined by comparing the modification timestamp of the staleFile and the source files.
         //
         final File staleFile = getStaleFile();
         final String debugPrefix = "StaleFile [" + FileSystemUtilities.getCanonicalPath(staleFile) + "]";
 
         boolean stale = !staleFile.exists();
         if (stale) {
             getLog().debug(debugPrefix + " not found. XML Schema (re-)generation required.");
         } else {
 
             final List<URL> sources = getSources();
 
             if (getLog().isDebugEnabled()) {
                 getLog().debug(debugPrefix + " found. Checking timestamps on source Java "
                         + "files to determine if XML Schema (re-)generation is required.");
             }
 
             final long staleFileLastModified = staleFile.lastModified();
             for (URL current : sources) {
 
                 final URLConnection sourceFileConnection;
                 try {
                     sourceFileConnection = current.openConnection();
                     sourceFileConnection.connect();
                 } catch (Exception e) {
 
                     if (getLog().isDebugEnabled()) {
                         getLog().debug("Could not open a sourceFileConnection to [" + current + "]", e);
                     }
 
                     // Can't determine if the staleFile is younger than this source.
                     // Re-generate to be on the safe side.
                     stale = true;
                     break;
                 }
 
                 try {
                     if (sourceFileConnection.getLastModified() > staleFileLastModified) {
 
                         if (getLog().isDebugEnabled()) {
                             getLog().debug(current.toString() + " is newer than the stale flag file.");
                         }
                         stale = true;
                     }
                 } finally {
                     if (sourceFileConnection instanceof HttpURLConnection) {
                         ((HttpURLConnection) sourceFileConnection).disconnect();
                     }
                 }
             }
         }
 
         // All done.
         return stale;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     protected boolean performExecution() throws MojoExecutionException, MojoFailureException {
 
         boolean updateStaleFileTimestamp = false;
         ToolExecutionEnvironment environment = null;
 
         try {
 
             //
             // Ensure that classes that SchemaGen expects to be loaded in the SystemToolClassLoader
             // is delegated to that ClassLoader, to comply with SchemaGen's internal reflective loading
             // of classes. Otherwise we will have ClassCastExceptions instead of proper execution.
             //
             final ClassRealm localRealm = (ClassRealm) getClass().getClassLoader();
             for (String current : SYSTEM_TOOLS_CLASSLOADER_PACKAGES) {
                 localRealm.importFrom(ToolProvider.getSystemToolClassLoader(), current);
             }
 
             // Configure the ThreadContextClassLoaderBuilder, to enable synthesizing a correct ClassPath for the tool.
             final ThreadContextClassLoaderBuilder classLoaderBuilder = ThreadContextClassLoaderBuilder
                     .createFor(this.getClass(), getLog(), getEncoding(false))
                     .addPaths(getClasspath())
                     .addPaths(getProject().getCompileSourceRoots());
 
             final LocaleFacet localeFacet = locale == null ? null : LocaleFacet.createFor(locale, getLog());
 
             // Create the execution environment as required by the XJC tool.
             environment = new ToolExecutionEnvironment(
                     getLog(),
                     classLoaderBuilder,
                     LoggingHandlerEnvironmentFacet.create(getLog(), getClass(), getEncoding(false)),
                     localeFacet);
             final String projectBasedirPath = FileSystemUtilities.getCanonicalPath(getProject().getBasedir());
 
             // Add any extra configured EnvironmentFacets, as configured in the POM.
             if (extraFacets != null) {
                 for (EnvironmentFacet current : extraFacets) {
                     environment.add(current);
                 }
             }
 
             // Setup the environment.
             environment.setup();
 
             // Compile the SchemaGen arguments
             final File episodeFile = getEpisodeFile(episodeFileName);
             final List<URL> sources = getSources();
             final String[] schemaGenArguments = getSchemaGenArguments(
                     environment.getClassPathAsArgument(),
                     episodeFile,
                     sources);
 
             // Ensure that the outputDirectory and workDirectory exists.
             // Clear them if configured to do so.
             FileSystemUtilities.createDirectory(getOutputDirectory(), clearOutputDir);
             FileSystemUtilities.createDirectory(getWorkDirectory(), clearOutputDir);
 
             // Re-generate the episode file's parent directory.
             getEpisodeFile(episodeFileName);
             // Do we need to re-create the episode file's parent directory?
             /*final boolean reCreateEpisodeFileParentDirectory = generateEpisode && clearOutputDir;
             if (reCreateEpisodeFileParentDirectory) {
 
             }
             */
 
             try {
 
                 // Check the system properties.
                 // logSystemPropertiesAndBasedir();
 
                 // Fire the SchemaGenerator
                 final int result = SchemaGenerator.run(
                         schemaGenArguments,
                         Thread.currentThread().getContextClassLoader());
 
                 if (SCHEMAGEN_INCORRECT_OPTIONS == result) {
                     printSchemaGenCommandAndThrowException(projectBasedirPath,
                             sources,
                             schemaGenArguments,
                             result,
                             null);
                 } else if (SCHEMAGEN_JAXB_ERRORS == result) {
 
                     // TODO: Collect the error message(s) which was emitted by SchemaGen. How can this be done?
                     throw new MojoExecutionException("JAXB errors arose while SchemaGen compiled sources to XML.");
                 }
 
                 // Copy generated XSDs and episode files from the WorkDirectory to the OutputDirectory,
                 // but do not copy the intermediary bytecode files generated by schemagen.
                 final List<Filter<File>> exclusionFilters = PatternFileFilter.createIncludeFilterList(
                         getLog(), "\\.class");
 
                 final List<File> toCopy = FileSystemUtilities.resolveRecursively(
                         Arrays.asList(getWorkDirectory()),
                         exclusionFilters, getLog());
                 for (File current : toCopy) {
 
                     // Get the path to the current file
                     final String currentPath = FileSystemUtilities.getCanonicalPath(current.getAbsoluteFile());
                     final File target = new File(getOutputDirectory(),
                             FileSystemUtilities.relativize(currentPath, getWorkDirectory(), true));
 
                     // Copy the file to the same relative structure within the output directory.
                     FileSystemUtilities.createDirectory(target.getParentFile(), false);
                     FileUtils.copyFile(current, target);
                 }
 
                 //
                 // The XSD post-processing should be applied in the following order:
                 //
                 // 1. [XsdAnnotationProcessor]:            Inject JavaDoc annotations for Classes.
                 // 2. [XsdEnumerationAnnotationProcessor]: Inject JavaDoc annotations for Enums.
                 // 3. [ChangeNamespacePrefixProcessor]:    Change namespace prefixes within XSDs.
                 // 4. [ChangeFilenameProcessor]:           Change the fileNames of XSDs.
                 //
 
                 final boolean performPostProcessing = createJavaDocAnnotations || transformSchemas != null;
                 if (performPostProcessing) {
 
                     // Map the XML Namespaces to their respective XML URIs (and reverse)
                     // The keys are the generated 'vanilla' XSD file names.
                     final Map<String, SimpleNamespaceResolver> resolverMap =
                             XsdGeneratorHelper.getFileNameToResolverMap(getOutputDirectory());
 
                     if (createJavaDocAnnotations) {
 
                         if (getLog().isInfoEnabled()) {
                             getLog().info("XSD post-processing: Adding JavaDoc annotations in generated XSDs.");
                         }
 
                         // Resolve the sources
                         final List<File> fileSources = new ArrayList<File>();
                         for (URL current : sources) {
                             if ("file".equalsIgnoreCase(current.getProtocol())) {
                                 final File toAdd = new File(current.getPath());
                                 if (toAdd.exists()) {
                                     fileSources.add(toAdd);
                                 } else {
                                     if (getLog().isWarnEnabled()) {
                                         getLog().warn("Ignoring URL [" + current + "] as it is a nonexistent file.");
                                     }
                                 }
                             }
                         }
 
                         final List<File> files = FileSystemUtilities.resolveRecursively(
                                 fileSources, null, getLog());
 
                         // Acquire JavaDocs
                         final JavaDocExtractor extractor = new JavaDocExtractor(getLog()).addSourceFiles(files);
                         final SearchableDocumentation javaDocs = extractor.process();
 
                         // Modify the 'vanilla' generated XSDs by inserting the JavaDoc as annotations
                         final JavaDocRenderer renderer = javaDocRenderer == null
                                 ? STANDARD_JAVADOC_RENDERER
                                 : javaDocRenderer;
                         final int numProcessedFiles = XsdGeneratorHelper.insertJavaDocAsAnnotations(getLog(),
                                 getEncoding(false),
                                 getOutputDirectory(),
                                 javaDocs,
                                 renderer);
 
                         if (getLog().isDebugEnabled()) {
                             getLog().info("XSD post-processing: " + numProcessedFiles + " files processed.");
                         }
                     }
 
                     if (transformSchemas != null) {
 
                         if (getLog().isInfoEnabled()) {
                             getLog().info("XSD post-processing: Renaming and converting XSDs.");
                         }
 
                         // Transform all namespace prefixes as requested.
                         XsdGeneratorHelper.replaceNamespacePrefixes(resolverMap,
                                 transformSchemas,
                                 getLog(),
                                 getOutputDirectory(),
                                 getEncoding(false));
 
                         // Rename all generated schema files as requested.
                         XsdGeneratorHelper.renameGeneratedSchemaFiles(resolverMap,
                                 transformSchemas,
                                 getLog(),
                                 getOutputDirectory(),
                                 getEncoding(false));
                     }
                 }
 
             } catch (MojoExecutionException e) {
                 throw e;
             } catch (Exception e) {
 
                 // Find the root exception, and print its stack trace to the Maven Log.
                 // These invocation target exceptions tend to produce really deep stack traces,
                 // hiding the actual root cause of the exception.
                 Throwable current = e;
                 while (current.getCause() != null) {
                     current = current.getCause();
                 }
 
                 getLog().error("Execution failed.");
 
                 //
                 // Print a stack trace
                 //
                 StringBuilder rootCauseBuilder = new StringBuilder();
                 rootCauseBuilder.append("\n");
                 rootCauseBuilder.append("[Exception]: " + current.getClass().getName() + "\n");
                 rootCauseBuilder.append("[Message]: " + current.getMessage() + "\n");
                 for (StackTraceElement el : current.getStackTrace()) {
                     rootCauseBuilder.append("         " + el.toString()).append("\n");
                 }
                 getLog().error(rootCauseBuilder.toString().replaceAll("[\r\n]+", "\n"));
 
                 printSchemaGenCommandAndThrowException(projectBasedirPath,
                         sources,
                         schemaGenArguments,
                         -1,
                         current);
 
             }
 
             // Indicate that the output directory was updated.
             getBuildContext().refresh(getOutputDirectory());
 
             // Update the modification timestamp of the staleFile.
             updateStaleFileTimestamp = true;
 
         } finally {
 
             // Restore the environment
             if (environment != null) {
                 environment.restore();
             }
         }
 
         // Add generated directories to
 
         // All done.
         return updateStaleFileTimestamp;
     }
 
     /**
      * @return The working directory to which the SchemaGenerator should initially copy all its generated files,
      * including bytecode files, compiled from java sources.
      */
     protected abstract File getWorkDirectory();
 
     /**
      * Finds a List containing URLs to compiled bytecode files within this Compilation Unit.
      * Typically this equals the resolved files under the project's build directories, plus any
      * JAR artifacts found on the classpath.
      *
      * @return A non-null List containing URLs to bytecode files within this compilation unit.
      * Typically this equals the resolved files under the project's build directories, plus any JAR
      * artifacts found on the classpath.
      */
     protected abstract List<URL> getCompiledClassNames();
 
     /**
      * Override this method to acquire a List holding all URLs to the SchemaGen Java sources for which this
      * AbstractXsdGeneratorMojo should generate Xml Schema Descriptor files.
      *
      * @return A non-null List holding URLs to sources for the XSD generation.
      */
     @Override
     protected abstract List<URL> getSources();
 
     //
     // Private helpers
     //
 
     private String[] getSchemaGenArguments(final String classPath,
                                            final File episodeFile,
                                            final List<URL> sources)
             throws MojoExecutionException {
 
         final ArgumentBuilder builder = new ArgumentBuilder();
 
         // Add all flags on the form '-flagName'
         // builder.withFlag();
 
         // Add all arguments on the form '-argumentName argumentValue'
         // (i.e. in 2 separate elements of the returned String[])
         builder.withNamedArgument("encoding", getEncoding(true));
         builder.withNamedArgument("d", getWorkDirectory().getAbsolutePath());
         builder.withNamedArgument("classpath", classPath);
 
         // From 2.4: Always generate an episode file.
         //
         builder.withNamedArgument("episode", FileSystemUtilities.getCanonicalPath(episodeFile));
 
         try {
 
             //
             // The SchemaGenerator does not support directories as arguments:
             // "Caused by: java.lang.IllegalArgumentException: directories not supported"
             // ... implying we must resolve source files in the compilation unit.
             //
             // There seems to be two ways of adding sources to the SchemaGen tool:
             // 1) Using java source files
             //    Define the relative paths to source files, calculated from the System.property "user.dir"
             //    (i.e. *not* the Maven "basedir" property) on the form 'src/main/java/se/west/something/SomeClass.java'.
             //    Sample: javac -d . ../github_jaxb2_plugin/src/it/schemagen-main/src/main/java/se/west/gnat/Foo.java
             //
             // 2) Using bytecode files
             //    Define the CLASSPATH to point to build output directories (such as target/classes), and then use
             //    package notation arguments on the form 'se.west.something.SomeClass'.
             //    Sample: schemagen -d . -classpath brat se.west.gnat.Foo
             //
             // The jaxb2-maven-plugin uses these two methods in the order given.
             //
             builder.withPreCompiledArguments(getSchemaGeneratorSourceFiles(sources));
         } catch (IOException e) {
             throw new MojoExecutionException("Could not compile source paths for the SchemaGenerator", e);
         }
 
         // All done.
         return logAndReturnToolArguments(builder.build(), "SchemaGen");
     }
 
     /**
      * <p>The SchemaGenerator does not support directories as arguments, implying we must resolve source
      * files in the compilation unit. This fact is shown when supplying a directory argument as source, when
      * the tool emits:
      * <blockquote>Caused by: java.lang.IllegalArgumentException: directories not supported</blockquote></p>
      * <p>There seems to be two ways of adding sources to the SchemaGen tool:</p>
      * <dl>
      * <dt>1. <strong>Java Source</strong> files</dt>
      * <dd>Define the relative paths to source files, calculated from the System.property {@code user.dir}
      * (i.e. <strong>not</strong> the Maven {@code basedir} property) on the form
      * {@code src/main/java/se/west/something/SomeClass.java}.<br/>
      * <em>Sample</em>: {@code javac -d . .
      * ./github_jaxb2_plugin/src/it/schemagen-main/src/main/java/se/west/gnat/Foo.java}</dd>
      * <dt>2. <strong>Bytecode</strong> files</dt>
      * <dd>Define the {@code CLASSPATH} to point to build output directories (such as target/classes), and then
      * use package notation arguments on the form {@code se.west.something.SomeClass}.<br/>
      * <em>Sample</em>: {@code schemagen -d . -classpath brat se.west.gnat.Foo}</dd>
      * </dl>
      * <p>The jaxb2-maven-plugin uses these two methods in the order given</p>
      *
      * @param sources The compiled sources (as calculated from the local project's
      *                source paths, {@code getSources()}).
      * @return A sorted List holding all sources to be used by the SchemaGenerator. According to the SchemaGenerator
      * documentation, the order in which the source arguments are provided is irrelevant.
      * The sources are to be rendered as the final (open-ended) argument to the schemagen execution.
      * @see #getSources()
      */
     private List<String> getSchemaGeneratorSourceFiles(final List<URL> sources)
             throws IOException, MojoExecutionException {
 
         final SortedMap<String, String> className2SourcePath = new TreeMap<String, String>();
         final File baseDir = getProject().getBasedir();
         final File userDir = new File(System.getProperty("user.dir"));
         final String encoding = getEncoding(true);
 
         // 1) Find/add all sources available in the compilation unit.
         for (URL current : sources) {
 
             final File sourceCodeFile = FileSystemUtilities.getFileFor(current, encoding);
 
             // Calculate the relative path for the current source
             final String relativePath = FileSystemUtilities.relativize(
                     FileSystemUtilities.getCanonicalPath(sourceCodeFile),
                     userDir,
                     true);
 
             if (getLog().isDebugEnabled()) {
                 getLog().debug("SourceCodeFile ["
                         + FileSystemUtilities.getCanonicalPath(sourceCodeFile)
                         + "] and userDir [" + FileSystemUtilities.getCanonicalPath(userDir)
                         + "] ==> relativePath: "
                         + relativePath
                         + ". (baseDir: " + FileSystemUtilities.getCanonicalPath(baseDir) + "]");
             }
 
             // Find the Java class(es) within the source.
             final JavaProjectBuilder builder = new JavaProjectBuilder();
             builder.setEncoding(encoding);
 
             //
             // Ensure that we include package-info.java classes in the SchemaGen compilation.
             //
             if (sourceCodeFile.getName().trim().equalsIgnoreCase(PACKAGE_INFO_FILENAME)) {
 
                 // For some reason, QDox requires the package-info.java to be added as a URL instead of a File.
                 builder.addSource(current);
                 final Collection<JavaPackage> packages = builder.getPackages();
                 if (packages.size() != 1) {
                     throw new MojoExecutionException("Exactly one package should be present in file ["
                             + sourceCodeFile.getPath() + "]");
                 }
 
                 // Make the key indicate that this is the package-info.java file.
                 final JavaPackage javaPackage = packages.iterator().next();
                 className2SourcePath.put("package-info for (" + javaPackage.getName() + ")", relativePath);
                 continue;
             }
 
             // This is not a package-info.java file, so QDox lets us add this as a File.
             builder.addSource(sourceCodeFile);
 
             // Map any found FQCN to the relativized path of its source file.
             for (JavaSource currentJavaSource : builder.getSources()) {
                 for (JavaClass currentJavaClass : currentJavaSource.getClasses()) {
 
                     final String className = currentJavaClass.getFullyQualifiedName();
                     if (className2SourcePath.containsKey(className)) {
                         if (getLog().isWarnEnabled()) {
                             getLog().warn("Already mapped. Source class [" + className + "] within ["
                                     + className2SourcePath.get(className)
                                     + "]. Not overwriting with [" + relativePath + "]");
                         }
                     } else {
                         className2SourcePath.put(className, relativePath);
                     }
                 }
             }
         }
 
         /*
         // 2) Find any bytecode available in the compilation unit, and add its file as a SchemaGen argument.
         //
         //    The algorithm is:
         //    1) Add bytecode classpath unless its class is already added in source form.
         //    2) SchemaGen cannot handle directory arguments, so any bytecode files in classpath directories
         //       must be resolved.
         //    3) All JARs in the classpath should be added as arguments to SchemaGen.
         //
         //    .... Gosh ...
         //
         for (URL current : getCompiledClassNames()) {
             getLog().debug(" (compiled ClassName) --> " + current.toExternalForm());
         }
 
         Filters.initialize(getLog(), CLASS_INCLUDE_FILTERS);
 
         final List<URL> classPathURLs = new ArrayList<URL>();
         for (String current : getClasspath()) {
 
             final File currentFile = new File(current);
             if (FileSystemUtilities.EXISTING_FILE.accept(currentFile)) {
 
                 // This is a file/JAR. Simply add its path to SchemaGen's arguments.
                 classPathURLs.add(FileSystemUtilities.getUrlFor(currentFile));
 
             } else if (FileSystemUtilities.EXISTING_DIRECTORY.accept(currentFile)) {
 
                 // Resolve all bytecode files within this directory.
                 // FileSystemUtilities.filterFiles(baseDir, )
                 if (getLog().isDebugEnabled()) {
                     getLog().debug("TODO: Resolve and add bytecode files within: ["
                             + FileSystemUtilities.getCanonicalPath(currentFile) + "]");
                 }
 
                 // Find the byte code files within the current directory.
                 final List<File> byteCodeFiles = new ArrayList<File>();
                 for(File currentResolvedFile : FileSystemUtilities.resolveRecursively(
                         Arrays.asList(currentFile), null, getLog())) {
 
                     if(Filters.matchAtLeastOnce(currentResolvedFile, CLASS_INCLUDE_FILTERS)) {
                         byteCodeFiles.add(currentResolvedFile);
                     }
                 }
 
                 for(File currentByteCodeFile : byteCodeFiles) {
 
                     final String currentCanonicalPath = FileSystemUtilities.getCanonicalPath(
                             currentByteCodeFile.getAbsoluteFile());
 
                     final String relativized = FileSystemUtilities.relativize(currentCanonicalPath,
                             FileSystemUtilities.getCanonicalFile(currentFile.getAbsoluteFile()));
                     final String pathFromUserDir = FileSystemUtilities.relativize(currentCanonicalPath, userDir);
 
                     final String className = relativized.substring(0, relativized.indexOf(".class"))
                             .replace("/", ".")
                             .replace(File.separator, ".");
 
                     if(!className2SourcePath.containsKey(className)) {
                         className2SourcePath.put(className, pathFromUserDir);
 
                         if(getLog().isDebugEnabled()) {
                             getLog().debug("Adding ByteCode [" + className + "] at relativized path ["
                                     + pathFromUserDir + "]");
                         }
                     } else {
                         if(getLog().isDebugEnabled()) {
                             getLog().debug("ByteCode [" + className + "] already added. Not re-adding.");
                         }
                     }
                 }
 
             } else if (getLog().isWarnEnabled()) {
 
                 final String suffix = !currentFile.exists() ? " nonexistent" : " was neither a File nor a Directory";
                 getLog().warn("Classpath part [" + current + "] " + suffix + ". Ignoring it.");
             }
         }
 
         /*
         for (URL current : getCompiledClassNames()) {
 
             // TODO: FIX THIS!
             // Get the class information data from the supplied URL
             for (String currentClassPathElement : getClasspath()) {
 
                 if(getLog().isDebugEnabled()) {
                     getLog().debug("Checking class path element: [" + currentClassPathElement + "]");
                 }
             }
 
             if(getLog().isDebugEnabled()) {
                 getLog().debug("Processing compiledClassName: [" + current + "]");
             }
 
             // Find the Java class(es) within the source.
             final JavaProjectBuilder builder = new JavaProjectBuilder();
             builder.setEncoding(getEncoding(true));
             builder.addSource(current);
 
             for (JavaSource currentSource : builder.getSources()) {
                 for (JavaClass currentClass : currentSource.getClasses()) {
 
                     final String className = currentClass.getFullyQualifiedName();
                     if (className2SourcePath.containsKey(className)) {
                         if (getLog().isWarnEnabled()) {
                             getLog().warn("Already mapped. Source class [" + className + "] within ["
                                     + className2SourcePath.get(className)
                                     + "]. Not overwriting with [" + className + "]");
                         }
                     } else {
                         className2SourcePath.put(className, className);
                     }
                 }
             }
         }
         */
 
         if (getLog().isDebugEnabled()) {
 
             final int size = className2SourcePath.size();
             getLog().debug("[ClassName-2-SourcePath Map (size: " + size + ")] ...");
 
             int i = 0;
             for (Map.Entry<String, String> current : className2SourcePath.entrySet()) {
                 getLog().debug("  " + (++i) + "/" + size + ": [" + current.getKey() + "]: "
                         + current.getValue());
             }
             getLog().debug("... End [ClassName-2-SourcePath Map]");
         }
 
         // Sort the source paths and place them first in the argument array
         final ArrayList<String> toReturn = new ArrayList<String>(className2SourcePath.values());
         Collections.sort(toReturn);
 
         // All Done.
         return toReturn;
     }
 
     private void printSchemaGenCommandAndThrowException(final String projectBasedirPath,
                                                         final List<URL> sources,
                                                         final String[] schemaGenArguments,
                                                         final int result,
                                                         final Throwable cause) throws MojoExecutionException {
 
         final StringBuilder errorMsgBuilder = new StringBuilder();
         errorMsgBuilder.append("\n+=================== [SchemaGenerator Error '"
                 + (result == -1 ? "<unknown>" : result) + "']\n");
         errorMsgBuilder.append("|\n");
         errorMsgBuilder.append("| SchemaGen did not complete its operation correctly.\n");
         errorMsgBuilder.append("|\n");
         errorMsgBuilder.append("| To re-create the error (and get a proper error message), cd to:\n");
         errorMsgBuilder.append("| ").append(projectBasedirPath).append("\n");
         errorMsgBuilder.append("| ... and fire the following on a command line/in a shell:\n");
         errorMsgBuilder.append("|\n");
 
         final StringBuilder builder = new StringBuilder("schemagen ");
         for (String current : schemaGenArguments) {
             builder.append(current).append(" ");
         }
 
         errorMsgBuilder.append("| " + builder.toString() + "\n");
         errorMsgBuilder.append("|\n");
         errorMsgBuilder.append("| The following source files should be processed by schemagen:\n");
 
         for (int i = 0; i < sources.size(); i++) {
             errorMsgBuilder.append("| " + i + ": ").append(sources.get(i).toString()).append("\n");
         }
 
         errorMsgBuilder.append("|\n");
         errorMsgBuilder.append("+=================== [End SchemaGenerator Error]\n");
 
         final String msg = errorMsgBuilder.toString().replaceAll("[\r\n]+", "\n");
         if (cause != null) {
             throw new MojoExecutionException(msg, cause);
         } else {
             throw new MojoExecutionException(msg);
         }
     }
 }