/*
 * Copyright 2010 the original author or authors.
 *
 * Licensed 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.
 */
package org.apache.maven.wrapper;

import java.io.File;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;

/**
 * @author Hans Dockter
 */
public class BootstrapMainStarter {
  public void start(String[] args, File mavenHome) throws Exception {
    File mavenJar = findLauncherJar(mavenHome);
    URLClassLoader contextClassLoader = new URLClassLoader(new URL[] {
      mavenJar.toURI().toURL()
    }, ClassLoader.getSystemClassLoader().getParent());
    Thread.currentThread().setContextClassLoader(contextClassLoader);
    Class<?> mainClass = contextClassLoader.loadClass("org.codehaus.plexus.classworlds.launcher.Launcher");

    System.setProperty("maven.home", mavenHome.getAbsolutePath());
    System.setProperty("classworlds.conf", new File(mavenHome, "/bin/m2.conf").getAbsolutePath());

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

  private File findLauncherJar(File mavenHome) {
    for (File file : new File(mavenHome, "boot").listFiles()) {
      if (file.getName().matches("plexus-classworlds-.*\\.jar")) {
        return file;
      }
    }
    throw new RuntimeException(String.format("Could not locate the Maven launcher JAR in Maven distribution '%s'.", mavenHome));
  }
}

/*
 * Copyright 2010 the original author or authors.
 *
 * Licensed 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.
 */
package org.apache.maven.wrapper;

import java.io.File;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;

/**
 * @author Hans Dockter
 */
public class BootstrapMainStarter {
  public void start(String[] args, File mavenHome) throws Exception {
    File mavenJar = findLauncherJar(mavenHome);
    URLClassLoader contextClassLoader = new URLClassLoader(new URL[] {
      mavenJar.toURI().toURL()
    }, ClassLoader.getSystemClassLoader().getParent());
    Thread.currentThread().setContextClassLoader(contextClassLoader);
    Class<?> mainClass = contextClassLoader.loadClass("org.codehaus.plexus.classworlds.launcher.Launcher");

    System.setProperty("maven.multiModuleProjectDirectory", System.getProperty("user.dir"));
    System.setProperty("maven.home", mavenHome.getAbsolutePath());
    System.setProperty("classworlds.conf", new File(mavenHome, "/bin/m2.conf").getAbsolutePath());

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

  private File findLauncherJar(File mavenHome) {
    for (File file : new File(mavenHome, "boot").listFiles()) {
      if (file.getName().matches("plexus-classworlds-.*\\.jar")) {
        return file;
      }
    }
    throw new RuntimeException(String.format("Could not locate the Maven launcher JAR in Maven distribution '%s'.", mavenHome));
  }  
}

Make sure the maven.multiModuleProjectDirectory envar is set for proper 3.3.1+ execution