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/* * Copyright (c) 2009, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation.  Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code 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 * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */package sun.net.ftp; import java.security.AccessController;import java.security.PrivilegedAction;import java.util.ServiceConfigurationError;//import sun.misc.Service; /** * Service provider class for FtpClient. * Sub-classes of FtpClientProvider provide an implementation of {@link FtpClient} * and associated classes. Applications do not normally use this class directly. * See {@link #provider() } for how providers are found and loaded. * * @since 1.7 */public abstract class FtpClientProvider {     /**     * Creates a FtpClient from this provider.     *     * @return The created {@link FtpClient}.     */    public abstract FtpClient createFtpClient();    private static final Object lock = new Object();    private static FtpClientProvider provider = null;     /**     * Initializes a new instance of this class.     *     * @throws SecurityException if a security manager is installed and it denies     *         {@link RuntimePermission}<tt>("ftpClientProvider")</tt>     */    protected FtpClientProvider() {        SecurityManager sm = System.getSecurityManager();        if (sm != null) {            sm.checkPermission(new RuntimePermission("ftpClientProvider"));        }    }     private static boolean loadProviderFromProperty() {        String cm = System.getProperty("sun.net.ftpClientProvider");        if (cm == null) {            return false;        }        try {            Class c = Class.forName(cm, true, null);            provider = (FtpClientProvider) c.newInstance();            return true;        } catch (ClassNotFoundException x) {            throw new ServiceConfigurationError(x.toString());        } catch (IllegalAccessException x) {            throw new ServiceConfigurationError(x.toString());        } catch (InstantiationException x) {            throw new ServiceConfigurationError(x.toString());        } catch (SecurityException x) {            throw new ServiceConfigurationError(x.toString());        }    }     private static boolean loadProviderAsService() {        //        Iterator i = Service.providers(FtpClientProvider.class,        //                ClassLoader.getSystemClassLoader());        //        while (i.hasNext()) {        //            try {        //                provider = (FtpClientProvider) i.next();        //                return true;        //            } catch (ServiceConfigurationError sce) {        //                if (sce.getCause() instanceof SecurityException) {        //                    // Ignore, try next provider, if any        //                    continue;        //                }        //                throw sce;        //            }        //        }        return false;    }     /**     * Returns the system wide default FtpClientProvider for this invocation of     * the Java virtual machine.     *     * <p> The first invocation of this method locates the default provider     * object as follows: </p>     *     * <ol>     *     *   <li><p> If the system property     *   <tt>java.net.FtpClientProvider</tt> is defined then it is     *   taken to be the fully-qualified name of a concrete provider class.     *   The class is loaded and instantiated; if this process fails then an     *   unspecified unchecked error or exception is thrown.  </p></li>     *     *   <li><p> If a provider class has been installed in a jar file that is     *   visible to the system class loader, and that jar file contains a     *   provider-configuration file named     *   <tt>java.net.FtpClientProvider</tt> in the resource     *   directory <tt>META-INF/services</tt>, then the first class name     *   specified in that file is taken.  The class is loaded and     *   instantiated; if this process fails then an unspecified unchecked error or exception is     *   thrown.  </p></li>     *     *   <li><p> Finally, if no provider has been specified by any of the above     *   means then the system-default provider class is instantiated and the     *   result is returned.  </p></li>     *     * </ol>     *     * <p> Subsequent invocations of this method return the provider that was     * returned by the first invocation.  </p>     *     * @return  The system-wide default FtpClientProvider     */    public static FtpClientProvider provider() {        synchronized (lock) {            if (provider != null) {                return provider;            }            return (FtpClientProvider) AccessController.doPrivileged(                    new PrivilegedAction<Object>() {                         public Object run() {                            if (loadProviderFromProperty()) {                                return provider;                            }                            if (loadProviderAsService()) {                                return provider;                            }                            provider = new sun.net.ftp.impl.DefaultFtpClientProvider();                            return provider;                        }                    });        }    }}