maven-wrapper/src/main/java/org/apache/maven/wrapper/BootstrapMainStarter.java

package org.apache.maven.wrapper;

/*
 * 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.FileNotFoundException;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.nio.file.DirectoryStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Iterator;
import java.util.Locale;
import java.util.Properties;

/**
 * Maven starter, from a provided Maven home directory.
 *
 * @author Hans Dockter
 */
public class BootstrapMainStarter
{
    public void start( String[] args, Path mavenHome, Properties properties )
        throws Exception
    {
        final Path mavenJar = findLauncherJar( mavenHome );
        URLClassLoader contextClassLoader = new URLClassLoader( new URL[] { mavenJar.toUri().toURL() },
                ClassLoader.getSystemClassLoader().getParent() );

        // can be useful to leak the classloader with some daemon mojo but generally a wrong idea so off by default
        if ( Boolean.parseBoolean( properties.getProperty( getClass().getName() + ".leakClassloader" ) ) )
        {
            doStart( args, mavenHome, properties, contextClassLoader );
            return;
        }

        try ( final URLClassLoader ref = contextClassLoader )
        {
            doStart( args, mavenHome, properties, contextClassLoader );
        }
    }

    private void doStart( final String[] args, final Path mavenHome,
                          final Properties properties,
                          final URLClassLoader contextClassLoader )
            throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException
    {
        Thread.currentThread().setContextClassLoader( contextClassLoader );
        Class<?> mainClass = contextClassLoader.loadClass( "org.codehaus.plexus.classworlds.launcher.Launcher" );

        System.setProperty( "maven.home", mavenHome.toAbsolutePath().toString() );
        System.setProperty( "classworlds.conf", getClassworldsConf( properties, mavenHome ) );

        Method mainMethod = mainClass.getMethod( "main", String[].class );
        mainMethod.invoke( null, new Object[] { args } );
    }

    private String getClassworldsConf( Properties properties, Path mavenHome )
    {
        final String override = properties.getProperty( "classworlds.conf" );
        if ( override != null )
        {
            return override;
        }
        return mavenHome.resolve( "bin/m2.conf" ).toAbsolutePath().toString();
    }

    private Path findLauncherJar( Path mavenHome )
        throws IOException
    {
        final Path mavenBoot = mavenHome.resolve( "boot" );
        if ( Files.isDirectory( mavenBoot ) )
        {
            try ( DirectoryStream<Path> ds = Files.newDirectoryStream( mavenBoot, "plexus-classworlds-*.jar" ) )
            {
                Iterator<Path> iterator = ds.iterator();
                if ( iterator.hasNext() )
                {
                    return iterator.next();
                }
            }
        }
        throw new FileNotFoundException( String.format( Locale.ROOT, "Could not locate the Maven launcher JAR"
            + " in Maven distribution '%s'.", mavenHome ) );
    }
}