src/main/java/org/apache/maven/plugins/shade/resource/ManifestResourceTransformer.java

package org.apache.maven.plugins.shade.resource;

/*
 * 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 org.apache.maven.plugins.shade.relocation.Relocator;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import java.util.Map;
import java.util.jar.Attributes;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;
import java.util.jar.JarOutputStream;
import java.util.jar.Manifest;

/**
 * A resource processor that allows the arbitrary addition of attributes to
 * the first MANIFEST.MF that is found in the set of JARs being processed, or
 * to a newly created manifest for the shaded JAR.
 *
 * @author Jason van Zyl
 * @since 1.2
 */
public class ManifestResourceTransformer
    implements ResourceTransformer
{

    // Configuration
    private String mainClass;

    private Map<String, Object> manifestEntries;

    // Fields
    private boolean manifestDiscovered;

    private Manifest manifest;

    public boolean canTransformResource( String resource )
    {
        if ( JarFile.MANIFEST_NAME.equalsIgnoreCase( resource ) )
        {
            return true;
        }

        return false;
    }

    public void processResource( String resource, InputStream is, List<Relocator> relocators )
        throws IOException
    {
        // We just want to take the first manifest we come across as that's our project's manifest. This is the behavior
        // now which is situational at best. Right now there is no context passed in with the processing so we cannot
        // tell what artifact is being processed.
        if ( !manifestDiscovered )
        {
            manifest = new Manifest( is );
            manifestDiscovered = true;
        }
    }

    public boolean hasTransformedResource()
    {
        return true;
    }

    public void modifyOutputStream( JarOutputStream jos )
        throws IOException
    {
        // If we didn't find a manifest, then let's create one.
        if ( manifest == null )
        {
            manifest = new Manifest();
        }

        Attributes attributes = manifest.getMainAttributes();

        if ( mainClass != null )
        {
            attributes.put( Attributes.Name.MAIN_CLASS, mainClass );
        }

        if ( manifestEntries != null )
        {
            for ( Map.Entry<String, Object> entry : manifestEntries.entrySet() )
            {
                attributes.put( new Attributes.Name( entry.getKey() ), entry.getValue() );
            }
        }

        jos.putNextEntry( new JarEntry( JarFile.MANIFEST_NAME ) );
        manifest.write( jos );
    }
}