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+/* 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;
+ }
+}