Launcher.java

/*
 * Copyright (c) 2009-present 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 com.planet57.gshell.launcher;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.Arrays;
import java.util.List;

/**
 * Bootstrap launcher.
 *
 * @author <a href="mailto:jason@planet57.com">Jason Dillon</a>
 * @since 2.0
 */
public final class Launcher
{
  private final Configuration config = new Configuration();

  public static void main(final String[] args) {
    new Launcher().run(args);
  }

  public void run(final String[] args) {
    Log.debug("Running");

    try {
      config.configure();

      launch(args);

      Log.debug("Exiting");

      System.exit(config.getSuccessExitCode());
    }
    catch (Throwable t) {
      Log.debug("Failure: ", t);
      t.printStackTrace();
      System.err.flush();
      System.exit(config.getFailureExitCode());
    }
  }

  public void launch(final String[] args) throws Exception {
    assert args != null;

    Log.debug("Launching");

    ClassLoader cl = getClassLoader();
    Class<?> type = cl.loadClass(config.getMainClass());
    Method method = getMainMethod(type);

    Thread.currentThread().setContextClassLoader(cl);

    Log.debug("Invoking: ", method, ", with args: ", Arrays.toString(args));

    try {
      method.invoke(null, new Object[]{args});
    }
    catch (InvocationTargetException e) {
      Log.debug("Invoke failed", e);

      Throwable cause = e.getTargetException();
      if (cause instanceof Exception) {
        throw (Exception) cause;
      }
      if (cause instanceof Error) {
        throw (Error) cause;
      }
      else {
        throw e;
      }
    }
  }

  private ClassLoader getClassLoader() throws Exception {
    List<URL> classPath = config.getClassPath();

    if (Log.DEBUG) {
      Log.debug("Classpath:");
      for (URL url : classPath) {
        Log.debug("    ", url);
      }
    }

    ClassLoader parent = getClass().getClassLoader();
    return new URLClassLoader(classPath.toArray(new URL[classPath.size()]), parent);
  }

  private Method getMainMethod(final Class<?> type) throws Exception {
    assert type != null;

    Method method = type.getMethod("main", String[].class);
    int modifiers = method.getModifiers();

    if (Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers) && method.getReturnType() == Void.TYPE) {
      return method;
    }

    throw new NoSuchMethodException("public static void main(String[] args) in " + type);
  }
}