[MJAR-238] Allow setting of module main class

Closes #2 from plamentotev:modular-jar-files

pom.xml

@@ -76,6 +76,7 @@
 
   <properties>
     <mavenArchiverVersion>3.3.0</mavenArchiverVersion>
+    <mavenFileManagementVersion>3.0.0</mavenFileManagementVersion>
     <mavenVersion>3.0</mavenVersion>
     <javaVersion>7</javaVersion>
   </properties>
@@ -96,6 +97,11 @@
       <artifactId>maven-artifact</artifactId>
       <version>${mavenVersion}</version>
     </dependency>
+    <dependency>
+      <groupId>org.apache.maven.shared</groupId>
+      <artifactId>file-management</artifactId>
+      <version>${mavenFileManagementVersion}</version>
+    </dependency>
     <dependency>
       <groupId>org.apache.maven</groupId>
       <artifactId>maven-archiver</artifactId>

src/it/MJAR-238-modular-jar-main-class/invoker.properties

@@ -0,0 +1,18 @@
+# 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.
+
+invoker.java.version = 9+

src/it/MJAR-238-modular-jar-main-class/pom.xml

@@ -0,0 +1,57 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  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.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>org.apache.maven.plugins</groupId>
+  <artifactId>mjar-238-modular-jar-main-class</artifactId>
+  <name>mjar-238-modular-jar-main-class</name>
+  <description>Verifies that the modular descriptor main class is set for modular Jar files</description>
+  <packaging>jar</packaging>
+  <version>1.0-SNAPSHOT</version>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-jar-plugin</artifactId>
+        <version>@project.version@</version>
+        <configuration>
+          <archive>
+            <manifest>
+              <mainClass>myproject.HelloWorld</mainClass>
+            </manifest>
+          </archive>
+        </configuration>
+      </plugin>
+    </plugins>
+
+    <pluginManagement>
+      <plugins>
+        <plugin>
+          <artifactId>maven-compiler-plugin</artifactId>
+          <configuration>
+            <source>1.9</source>
+            <target>1.9</target>
+          </configuration>
+        </plugin>
+      </plugins>
+    </pluginManagement>
+  </build>
+</project>

src/it/MJAR-238-modular-jar-main-class/src/main/java/module-info.java

@@ -0,0 +1,22 @@
+/*
+ * 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.
+ */
+
+module myproject {
+    exports myproject;
+}

src/it/MJAR-238-modular-jar-main-class/src/main/java/myproject/HelloWorld.java

@@ -0,0 +1,36 @@
+package myproject;
+
+/*
+ * 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.
+ */
+
+/**
+ * The classic Hello World App.
+ */
+public class HelloWorld {
+
+  /**
+     * Main method.
+     *
+     * @param args Not used
+     */
+    public static void main( String[] args )
+    {
+        System.out.println( "Hi!" );
+    } 
+}

src/it/MJAR-238-modular-jar-main-class/verify.bsh

@@ -0,0 +1,75 @@
+/*
+ * 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 java.io.*;
+import java.lang.module.*;
+import java.util.jar.*;
+
+boolean result = true;
+JarFile jar;
+
+try
+{
+    File target = new File( basedir, "target" );
+    if ( !target.exists() || !target.isDirectory() )
+    {
+        System.err.println( "target file is missing or not a directory." );
+        return false;
+    }
+
+    File artifact = new File( target, "mjar-238-modular-jar-main-class-1.0-SNAPSHOT.jar" );
+    if ( !artifact.exists() || artifact.isDirectory() )
+    {
+        System.err.println( "artifact file is missing or a directory." );
+        return false;
+    }
+
+    jar = new JarFile( artifact );
+
+    Attributes manifest = jar.getManifest().getMainAttributes();
+
+    if ( !"myproject.HelloWorld".equals( manifest.get( Attributes.Name.MAIN_CLASS ) ) )
+    {
+        System.err.println( "Manifest main class attribute not equals myproject.HelloWorld" );
+        return false;
+    }
+
+    InputStream moduleDescriptorInputStream = jar.getInputStream( jar.getEntry( "module-info.class" ) );
+    ModuleDescriptor moduleDescriptor = ModuleDescriptor.read( moduleDescriptorInputStream );
+
+    if ( !"myproject.HelloWorld".equals( moduleDescriptor.mainClass().orElse( null ) ) )
+    {
+        System.err.println( "Module descriptor main class not equals myproject.HelloWorld" );
+        return false;
+    }
+}
+catch( Throwable e )
+{
+    e.printStackTrace();
+    result = false;
+}
+finally
+{
+    if ( jar != null )
+    {
+        jar.close();
+    }
+}
+
+return result;

src/main/java/org/apache/maven/plugins/jar/AbstractJarMojo.java

@@ -28,10 +28,14 @@
 import org.apache.maven.plugins.annotations.Parameter;
 import org.apache.maven.project.MavenProject;
 import org.apache.maven.project.MavenProjectHelper;
+import org.apache.maven.shared.model.fileset.FileSet;
+import org.apache.maven.shared.model.fileset.util.FileSetManager;
 import org.codehaus.plexus.archiver.Archiver;
 import org.codehaus.plexus.archiver.jar.JarArchiver;
 
 import java.io.File;
+import java.util.Arrays;
+import java.util.Map;
 
 /**
  * Base class for creating a jar from project classes.
@@ -47,6 +51,8 @@ public abstract class AbstractJarMojo
 
     private static final String[] DEFAULT_INCLUDES = new String[] { "**/**" };
 
+    private static final String MODULE_DESCRIPTOR_FILE_NAME = "module-info.class";
+
     /**
      * List of files to include. Specified as fileset patterns which are relative to the input directory whose contents
      * is being packaged into the JAR.
@@ -76,8 +82,8 @@ public abstract class AbstractJarMojo
     /**
      * The Jar archiver.
      */
-    @Component( role = Archiver.class, hint = "jar" )
-    private JarArchiver jarArchiver;
+    @Component
+    private Map<String, Archiver> archivers;
 
     /**
      * The {@link {MavenProject}.
@@ -201,9 +207,41 @@ public File createArchive()
     {
         File jarFile = getJarFile( outputDirectory, finalName, getClassifier() );
 
+        FileSetManager fileSetManager = new FileSetManager();
+        FileSet jarContentFileSet = new FileSet();
+        jarContentFileSet.setDirectory( getClassesDirectory().getAbsolutePath() );
+        jarContentFileSet.setIncludes( Arrays.asList( getIncludes() ) );
+        jarContentFileSet.setExcludes( Arrays.asList( getExcludes() ) );
+
+        boolean containsModuleDescriptor = false;
+        String[] includedFiles = fileSetManager.getIncludedFiles( jarContentFileSet );
+        for ( String includedFile : includedFiles )
+        {
+            // May give false positives if the files is named as module descriptor
+            // but is not in the root of the archive or in the versioned area
+            // (and hence not actually a module descriptor).
+            // That is fine since the modular Jar archiver will gracefully
+            // handle such case.
+            // And also such case is unlikely to happen as file ending
+            // with "module-info.class" is unlikely to be included in Jar file
+            // unless it is a module descriptor.
+            if ( includedFile.endsWith( MODULE_DESCRIPTOR_FILE_NAME ) )
+            {
+                containsModuleDescriptor = true;
+                break;
+            }
+        }
+
         MavenArchiver archiver = new MavenArchiver();
 
-        archiver.setArchiver( jarArchiver );
+        if ( containsModuleDescriptor )
+        {
+            archiver.setArchiver( (JarArchiver) archivers.get( "mjar" ) );
+        }
+        else
+        {
+            archiver.setArchiver( (JarArchiver) archivers.get( "jar" ) );
+        }
 
         archiver.setOutputFile( jarFile );
 

src/site/apt/usage.apt.vm

@@ -78,3 +78,22 @@ mvn package
   the {{{/guides/introduction/introduction-to-the-lifecycle.html}Maven Build Life Cycle}}.
 
   For full documentation, click {{{./plugin-info.html}here}}.
+
+* Modular JAR files
+
+  The {{{https://openjdk.java.net/projects/jigsaw/spec/}Java Platform Module System (JPMS)}} introduced
+  {{{https://cr.openjdk.java.net/~mr/jigsaw/spec/jar.html}changes in the JAR file specifications}}
+  as well - Modular JAR files. Modular JAR files are JAR files with <<<module-info.class>>> file in the root directory
+  (or in the versioned area for multi-release JAR files). If the project contains <<<module-info.class>>>
+  the resulting JAR will be a Modular JAR without a need for any configuration regardless of the plugin version used.
+
+  Starting with version 3.1.2, if the JAR file contains <<<module-info.class>>>, this plugin will update
+  the modular descriptor (<<<module-info.class>>>) with additional attributes such as the list of packages included
+  and will validate the resulting modular descriptor (for example if all services provided by the module are actually
+  included in the JAR file). The most notable additional attribute added is the module main class.
+  If the JAR manifest contains <<<Main-Class>>> attribute this plugin will set the module main class to the same value
+  (for example how to set it read {{{../../shared/maven-archiver/examples/classpath.html}Make The Jar Executable}}).
+  Internally the plugin uses the JDK <<<jar>>> tool so in order to add the additional attributes and to
+  verify the modular descriptor Maven should be run with JDK version 9 or newer. If version 8 or earlier is used
+  the resulting JAR still will be Modular JAR (as it contains <<<module-info.class>>>) but no additional attributes
+  will be added and no validation will be performed.