ExtensionDescriptorBuilder.java

package org.apache.maven.project;

/*
 * 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.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.jar.JarFile;
import java.util.zip.ZipEntry;

import org.codehaus.plexus.util.IOUtil;
import org.codehaus.plexus.util.ReaderFactory;
import org.codehaus.plexus.util.xml.Xpp3Dom;
import org.codehaus.plexus.util.xml.Xpp3DomBuilder;
import org.codehaus.plexus.util.xml.pull.XmlPullParserException;

/**
 * Creates an extension descriptor from some XML stream.
 * 
 * @author Benjamin Bentmann
 */
class ExtensionDescriptorBuilder
{

    private String getExtensionDescriptorLocation()
    {
        return "META-INF/maven/extension.xml";
    }

    /**
     * Extracts the extension descriptor (if any) from the specified JAR file.
     * 
     * @param extensionJar The JAR file or directory to extract the descriptor from, must not be {@code null}.
     * @return The extracted descriptor or {@code null} if no descriptor was found.
     * @throws IOException If the descriptor is present but could not be parsed.
     */
    public ExtensionDescriptor build( File extensionJar )
        throws IOException
    {
        ExtensionDescriptor extensionDescriptor = null;

        if ( extensionJar.isFile() )
        {
            JarFile pluginJar = new JarFile( extensionJar, false );
            try
            {
                ZipEntry pluginDescriptorEntry = pluginJar.getEntry( getExtensionDescriptorLocation() );

                if ( pluginDescriptorEntry != null )
                {
                    InputStream is = pluginJar.getInputStream( pluginDescriptorEntry );

                    extensionDescriptor = build( is );
                }
            }
            finally
            {
                pluginJar.close();
            }
        }
        else
        {
            File pluginXml = new File( extensionJar, getExtensionDescriptorLocation() );

            if ( pluginXml.canRead() )
            {
                InputStream is = new BufferedInputStream( new FileInputStream( pluginXml ) );
                try
                {
                    extensionDescriptor = build( is );
                }
                finally
                {
                    IOUtil.close( is );
                }
            }
        }

        return extensionDescriptor;
    }

    ExtensionDescriptor build( InputStream is )
        throws IOException
    {
        ExtensionDescriptor extensionDescriptor = new ExtensionDescriptor();

        Xpp3Dom dom;
        try
        {
            dom = Xpp3DomBuilder.build( ReaderFactory.newXmlReader( is ) );
        }
        catch ( XmlPullParserException e )
        {
            throw (IOException) new IOException( e.getMessage() ).initCause( e );
        }
        finally
        {
            IOUtil.close( is );
        }

        if ( !"extension".equals( dom.getName() ) )
        {
            throw new IOException( "Unexpected root element \"" + dom.getName() + "\", expected \"extension\"" );
        }

        extensionDescriptor.setExportedPackages( parseStrings( dom.getChild( "exportedPackages" ) ) );

        extensionDescriptor.setExportedArtifacts( parseStrings( dom.getChild( "exportedArtifacts" ) ) );

        return extensionDescriptor;
    }

    private List<String> parseStrings( Xpp3Dom dom )
    {
        List<String> strings = null;

        if ( dom != null )
        {
            strings = new ArrayList<String>();

            for ( Xpp3Dom child : dom.getChildren() )
            {
                String string = child.getValue();
                if ( string != null )
                {
                    string = string.trim();
                    if ( string.length() > 0 )
                    {
                        strings.add( string );
                    }
                }
            }
        }

        return strings;
    }

}