src/main/java/org/apache/maven/plugins/shade/resource/ComponentsXmlResourceTransformer.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 org.codehaus.plexus.util.ReaderFactory;
import org.codehaus.plexus.util.WriterFactory;
import org.codehaus.plexus.util.xml.Xpp3Dom;
import org.codehaus.plexus.util.xml.Xpp3DomBuilder;
import org.codehaus.plexus.util.xml.Xpp3DomWriter;

import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.io.Writer;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.jar.JarEntry;
import java.util.jar.JarOutputStream;

/**
 * A resource processor that aggregates plexus <code>components.xml</code> files.
 */
public class ComponentsXmlResourceTransformer
    implements ResourceTransformer
{
    private Map<String, Xpp3Dom> components = new LinkedHashMap<>();

    public static final String COMPONENTS_XML_PATH = "META-INF/plexus/components.xml";

    public boolean canTransformResource( String resource )
    {
        return COMPONENTS_XML_PATH.equals( resource );
    }

    public void processResource( String resource, InputStream is, List<Relocator> relocators )
        throws IOException
    {
        Xpp3Dom newDom;

        try
        {
            BufferedInputStream bis = new BufferedInputStream( is )
            {
                public void close()
                    throws IOException
                {
                    // leave ZIP open
                }
            };

            Reader reader = ReaderFactory.newXmlReader( bis );

            newDom = Xpp3DomBuilder.build( reader );
        }
        catch ( Exception e )
        {
            throw new IOException( "Error parsing components.xml in " + is, e );
        }

        // Only try to merge in components if there are some elements in the component-set
        if ( newDom.getChild( "components" ) == null )
        {
            return;
        }

        Xpp3Dom[] children = newDom.getChild( "components" ).getChildren( "component" );

        for ( Xpp3Dom component : children )
        {
            String role = getValue( component, "role" );
            role = getRelocatedClass( role, relocators );
            setValue( component, "role", role );

            String roleHint = getValue( component, "role-hint" );

            String impl = getValue( component, "implementation" );
            impl = getRelocatedClass( impl, relocators );
            setValue( component, "implementation", impl );

            String key = role + ':' + roleHint;
            if ( components.containsKey( key ) )
            {
                // TODO: use the tools in Plexus to merge these properly. For now, I just need an all-or-nothing
                // configuration carry over

                Xpp3Dom dom = components.get( key );
                if ( dom.getChild( "configuration" ) != null )
                {
                    component.addChild( dom.getChild( "configuration" ) );
                }
            }

            Xpp3Dom requirements = component.getChild( "requirements" );
            if ( requirements != null && requirements.getChildCount() > 0 )
            {
                for ( int r = requirements.getChildCount() - 1; r >= 0; r-- )
                {
                    Xpp3Dom requirement = requirements.getChild( r );

                    String requiredRole = getValue( requirement, "role" );
                    requiredRole = getRelocatedClass( requiredRole, relocators );
                    setValue( requirement, "role", requiredRole );
                }
            }

            components.put( key, component );
        }
    }

    public void modifyOutputStream( JarOutputStream jos )
        throws IOException
    {
        byte[] data = getTransformedResource();

        jos.putNextEntry( new JarEntry( COMPONENTS_XML_PATH ) );

        jos.write( data );

        components.clear();
    }

    public boolean hasTransformedResource()
    {
        return !components.isEmpty();
    }

    byte[] getTransformedResource()
        throws IOException
    {
        ByteArrayOutputStream baos = new ByteArrayOutputStream( 1024 * 4 );

        try ( Writer writer = WriterFactory.newXmlWriter( baos ) )
        {
            Xpp3Dom dom = new Xpp3Dom( "component-set" );

            Xpp3Dom componentDom = new Xpp3Dom( "components" );

            dom.addChild( componentDom );

            for ( Xpp3Dom component : components.values() )
            {
                componentDom.addChild( component );
            }

            Xpp3DomWriter.write( writer, dom );
        }

        return baos.toByteArray();
    }

    private String getRelocatedClass( String className, List<Relocator> relocators )
    {
        if ( className != null && className.length() > 0 && relocators != null )
        {
            for ( Relocator relocator : relocators )
            {
                if ( relocator.canRelocateClass( className ) )
                {
                    return relocator.relocateClass( className );
                }
            }
        }

        return className;
    }

    private static String getValue( Xpp3Dom dom, String element )
    {
        Xpp3Dom child = dom.getChild( element );

        return ( child != null && child.getValue() != null ) ? child.getValue() : "";
    }

    private static void setValue( Xpp3Dom dom, String element, String value )
    {
        Xpp3Dom child = dom.getChild( element );

        if ( child == null || value == null || value.length() <= 0 )
        {
            return;
        }

        child.setValue( value );
    }

}