Subversion Repositories openrisc

/* ServiceProviderLoadingAction.java -- Action for loading plug-in services.

   Copyright (C) 2004  Free Software Foundation

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 2, or (at your option)

any later version.

GNU Classpath is distributed in the hope that it will be useful, but

WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

General Public License for more details.

You should have received a copy of the GNU General Public License

along with GNU Classpath; see the file COPYING.  If not, write to the

Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301 USA.

Linking this library statically or dynamically with other modules is

making a combined work based on this library.  Thus, the terms and

conditions of the GNU General Public License cover the whole

combination.

As a special exception, the copyright holders of this library give you

permission to link this library with independent modules to produce an

executable, regardless of the license terms of these independent

modules, and to copy and distribute the resulting executable under

terms of your choice, provided that you also meet, for each linked

independent module, the terms and conditions of the license of that

module.  An independent module is a module which is not derived from

or based on this library.  If you modify this library, you may extend

this exception to your version of the library, but you are not

obligated to do so.  If you do not wish to do so, delete this

exception statement from your version. */

package gnu.classpath;

import java.security.PrivilegedExceptionAction;

/**

 * A privileged action for creating a new instance of a service

 * provider.

 *

 * <p>Class loading and instantiation is encapsulated in a

 * <code>PriviledgedAction</code> in order to restrict the loaded

 * service providers to the {@link java.security.AccessControlContext}

 * that was active when {@link

 * gnu.classpath.ServiceFactory#lookupProviders(Class, ClassLoader)} was

 * called, even though the actual loading is delayed to the time when the

 * provider is actually needed.

 *

 * @author <a href="mailto:brawer@dandelis.ch">Sascha Brawer</a>

 */

final class ServiceProviderLoadingAction<P>

  implements PrivilegedExceptionAction<P>

{

  /**

   * The interface to which the loaded service provider implementation

   * must conform.  Usually, this is a Java interface type, but it

   * might also be an abstract class or even a concrete class.

   */

  private final Class<P> spi;

  /**

   * The fully qualified name of the class that gets loaded when

   * this action is executed.

   */

  private final String providerName;

  /**

   * The ClassLoader that gets used for loading the service provider

   * class.

   */

  private final ClassLoader loader;

  /**

   * Constructs a privileged action for loading a service provider.

   *

   * @param spi the interface to which the loaded service provider

   * implementation must conform. Usually, this is a Java interface

   * type, but it might also be an abstract class or even a concrete

   * superclass.

   *

   * @param providerName the fully qualified name of the class that

   * gets loaded when this action is executed.

   *

   * @param loader the ClassLoader that gets used for loading the

   * service provider class.

   *

   * @throws IllegalArgumentException if <code>spi</code>,

   * <code>providerName</code> or <code>loader</code> is

   * <code>null</code>.

   */

  ServiceProviderLoadingAction(Class<P> spi, String providerName,

                               ClassLoader loader)

  {

    if (spi == null || providerName == null || loader == null)

      throw new IllegalArgumentException();

    this.spi = spi;

    this.providerName = providerName;

    this.loader = loader;

  }

  /**

   * Loads an implementation class for a service provider, and creates

   * a new instance of the loaded class by invoking its public

   * no-argument constructor.

   *

   * @return a new instance of the class whose name was passed as

   * <code>providerName</code> to the constructor.

   *

   * @throws ClassCastException if the service provider does not

   * implement the <code>spi</code> interface that was passed to the

   * constructor.

   *

   * @throws IllegalAccessException if the service provider class or

   * its no-argument constructor are not <code>public</code>.

   *

   * @throws InstantiationException if the service provider class is

   * <code>abstract</code>, an interface, a primitive type, an array

   * class, or void; or if service provider class does not have a

   * no-argument constructor; or if there some other problem with

   * creating a new instance of the service provider.

   */

  public P run()

    throws Exception

  {

    Class<P> loadedClass;

    P serviceProvider;

    loadedClass = (Class<P>) loader.loadClass(providerName);

    serviceProvider = loadedClass.newInstance();

    // Ensure that the loaded provider is actually implementing

    // the service provider interface.

    if (!spi.isInstance(serviceProvider))

      throw new ClassCastException(spi.getName());

    return serviceProvider;

  }

}