Add Archiver that creates modular JAR files using the JDK jar tool.

It would allow clients of Plexus Archiver to specify
the version and the main class of a Java module.

Also the jar tool have the nice side effect
of verifying the resulting modular JAR file.

Closes #84, Closes #67, Closes #68

src/main/java/org/codehaus/plexus/archiver/jar/JarToolModularJarArchiver.java

@@ -0,0 +1,256 @@
+/**
+ *
+ * Copyright 2018 The Apache Software Foundation
+ *
+ * Licensed 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.
+ */
+package org.codehaus.plexus.archiver.jar;
+
+import org.apache.commons.compress.parallel.InputStreamSupplier;
+import org.codehaus.plexus.archiver.ArchiverException;
+import org.codehaus.plexus.archiver.util.ArchiveEntryUtils;
+import org.codehaus.plexus.archiver.util.ResourceUtils;
+import org.codehaus.plexus.archiver.zip.ConcurrentJarCreator;
+import org.codehaus.plexus.components.io.resources.PlexusIoResource;
+import org.codehaus.plexus.util.FileUtils;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.PrintStream;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.regex.Pattern;
+
+/**
+ * A {@link ModularJarArchiver} implementation that uses
+ * the {@code jar} tool provided by
+ * {@code java.util.spi.ToolProvider} to create
+ * modular JAR files.
+ *
+ * <p>
+ * The basic JAR archive is created by {@link JarArchiver}
+ * and the {@code jar} tool is used to upgrade it to modular JAR.
+ *
+ * <p>
+ * If the JAR file does not contain module descriptor
+ * or the JDK does not provide the {@code jar} tool
+ * (for example JDK prior to Java 9), then the
+ * archive created by {@link JarArchiver}
+ * is left unchanged.
+ */
+public class JarToolModularJarArchiver
+    extends ModularJarArchiver
+{
+    private static final String MODULE_DESCRIPTOR_FILE_NAME
+        = "module-info.class";
+
+    private static final Pattern MRJAR_VERSION_AREA
+        = Pattern.compile( "META-INF/versions/\\d+/" );
+
+    private Object jarTool;
+
+    private boolean moduleDescriptorFound;
+
+    private Path tempDir;
+
+    public JarToolModularJarArchiver()
+    {
+        try
+        {
+            Class<?> toolProviderClass =
+                Class.forName( "java.util.spi.ToolProvider" );
+            Object jarToolOptional = toolProviderClass
+                .getMethod( "findFirst", String.class )
+                .invoke( null, "jar" );
+
+            jarTool = jarToolOptional.getClass().getMethod( "get" )
+                .invoke( jarToolOptional );
+        }
+        catch ( ReflectiveOperationException | SecurityException e )
+        {
+            // Ignore. It is expected that the jar tool
+            // may not be available.
+        }
+    }
+
+    @Override
+    protected void zipFile( InputStreamSupplier is, ConcurrentJarCreator zOut,
+                            String vPath, long lastModified, File fromArchive,
+                            int mode, String symlinkDestination,
+                            boolean addInParallel )
+        throws IOException, ArchiverException
+    {
+        // We store the module descriptors in temporary location
+        // and then add it to the JAR file using the JDK jar tool.
+        // It may look strange at first, but to update a JAR file
+        // you need to add new files[1] and the only files
+        //  we're sure that exists in modular JAR file
+        // are the module descriptors.
+        //
+        // [1] There are some exceptions but we need at least one file to
+        // ensure it will work in all cases.
+        if ( jarTool != null && isModuleDescriptor( vPath ) )
+        {
+            getLogger().debug( "Module descriptor found: " + vPath );
+
+            moduleDescriptorFound = true;
+
+            // Copy the module descriptor to temporary directory
+            // so later then can be added to the JAR archive
+            // by the jar tool.
+
+            if ( tempDir == null )
+            {
+                tempDir = Files
+                    .createTempDirectory( "plexus-archiver-modular_jar-" );
+                tempDir.toFile().deleteOnExit();
+            }
+
+            File destFile = tempDir.resolve( vPath ).toFile();
+            destFile.getParentFile().mkdirs();
+            destFile.deleteOnExit();
+
+            ResourceUtils.copyFile( is.get(), destFile );
+            ArchiveEntryUtils.chmod( destFile,  mode );
+            destFile.setLastModified( lastModified == PlexusIoResource.UNKNOWN_MODIFICATION_DATE
+                                                      ? System.currentTimeMillis()
+                                                      : lastModified );
+        }
+        else
+        {
+            super.zipFile( is, zOut, vPath, lastModified,
+                fromArchive, mode, symlinkDestination, addInParallel );
+        }
+    }
+
+    @Override
+    protected void postCreateArchive()
+        throws ArchiverException
+    {
+        if ( !moduleDescriptorFound )
+        {
+            // no need to update the JAR archive
+            return;
+        }
+
+        try
+        {
+            getLogger().debug( "Using the jar tool to " +
+                "update the archive to modular JAR." );
+
+			Integer result = (Integer) jarTool.getClass()
+                .getMethod( "run",
+                    PrintStream.class, PrintStream.class, String[].class )
+                .invoke( jarTool,
+                    System.out, System.err,
+                    getJarToolArguments() );
+
+            if ( result != null && result != 0 )
+            {
+                throw new ArchiverException( "Could not create modular JAR file. " +
+                    "The JDK jar tool exited with " + result );
+            }
+        }
+        catch ( ReflectiveOperationException | SecurityException e )
+        {
+            throw new ArchiverException( "Exception occurred " +
+                "while creating modular JAR file", e );
+        }
+        finally
+        {
+            clearTempDirectory();
+        }
+    }
+
+    /**
+     * Returns {@code true} if {@code path}
+     * is a module descriptor.
+     */
+    private boolean isModuleDescriptor( String path )
+    {
+        if ( path.endsWith( MODULE_DESCRIPTOR_FILE_NAME ) )
+        {
+            String prefix = path.substring( 0,
+                path.lastIndexOf( MODULE_DESCRIPTOR_FILE_NAME ) );
+
+            // the path is a module descriptor if it located
+            // into the root of the archive or into the
+            // version are of a multi-release JAR file
+            return prefix.isEmpty() ||
+                MRJAR_VERSION_AREA.matcher( prefix ).matches();
+        }
+        else
+        {
+            return false;
+        }
+    }
+
+    /**
+     * Prepares the arguments for the jar tool.
+     * It takes into account the module version,
+     * main class, etc.
+     */
+    private String[] getJarToolArguments()
+    {
+        List<String> args = new ArrayList<>();
+
+        args.add( "--update" );
+        args.add( "--file" );
+        args.add( getDestFile().getAbsolutePath() );
+
+        if ( getModuleMainClass() != null )
+        {
+            args.add( "--main-class" );
+            args.add( getModuleMainClass() );
+        }
+
+        if ( getModuleVersion() != null )
+        {
+            args.add( "--module-version" );
+            args.add( getModuleVersion() );
+        }
+
+        if ( !isCompress() )
+        {
+            args.add( "--no-compress" );
+        }
+
+        args.add( "-C" );
+        args.add( tempDir.toFile().getAbsolutePath() );
+        args.add( "." );
+
+        return args.toArray( new String[]{} );
+    }
+
+    /**
+     * Makes best effort the clean up
+     * the temporary directory used.
+     */
+    private void clearTempDirectory()
+    {
+        try
+        {
+            if ( tempDir != null )
+            {
+                FileUtils.deleteDirectory( tempDir.toFile() );
+            }
+        }
+        catch ( IOException e )
+        {
+            // Ignore. It is just best effort.
+        }
+    }
+
+}

src/main/java/org/codehaus/plexus/archiver/jar/ModularJarArchiver.java

@@ -0,0 +1,76 @@
+/**
+ *
+ * Copyright 2018 The Apache Software Foundation
+ *
+ * Licensed 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.
+ */
+package org.codehaus.plexus.archiver.jar;
+
+/**
+ * Base class for creating modular JAR archives.
+ *
+ * Subclasses are required to be able to handle both
+ * JAR archives with module descriptor (modular JAR)
+ * and without ("regular" JAR).
+ * That would allow clients of this class to use
+ * it without prior knowledge if the classes
+ * they are going to add are part of module
+ * (contain module descriptor class) or not.
+ *
+ * @since 3.6
+ */
+public abstract class ModularJarArchiver
+    extends JarArchiver
+{
+    private String moduleMainClass;
+
+    private String moduleVersion;
+
+    public String getModuleMainClass()
+    {
+        return moduleMainClass;
+    }
+
+    /**
+     * Sets the module main class.
+     * Ignored if the JAR file does not contain
+     * module descriptor.
+     *
+     * <p>Note that implementations may choose
+     * to replace the value set in the manifest as well.
+     *
+     * @param moduleMainClass the module main class.
+     */
+    public void setModuleMainClass( String moduleMainClass )
+    {
+        this.moduleMainClass = moduleMainClass;
+    }
+
+    public String getModuleVersion()
+    {
+        return moduleVersion;
+    }
+
+    /**
+     * Sets the module version.
+     * Ignored if the JAR file does not contain
+     * module descriptor.
+     *
+     * @param moduleVersion the module version.
+     */
+    public void setModuleVersion( String moduleVersion )
+    {
+        this.moduleVersion = moduleVersion;
+    }
+
+}

src/main/resources/META-INF/plexus/components.xml

@@ -41,6 +41,12 @@
       <implementation>org.codehaus.plexus.archiver.jar.JarArchiver</implementation>
       <instantiation-strategy>per-lookup</instantiation-strategy>
     </component>
+    <component>
+      <role>org.codehaus.plexus.archiver.Archiver</role>
+      <role-hint>mjar</role-hint>
+      <implementation>org.codehaus.plexus.archiver.jar.JarToolModularJarArchiver</implementation>
+      <instantiation-strategy>per-lookup</instantiation-strategy>
+    </component>
 
     <component>
       <role>org.codehaus.plexus.archiver.Archiver</role>