1/*
2 * Copyright (c) 2009, 2011, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.  Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25package sun.net.ftp;
26
27import java.security.AccessController;
28import java.security.PrivilegedAction;
29import java.util.ServiceConfigurationError;
30//import java.util.ServiceLoader;
31
32/**
33 * Service provider class for FtpClient.
34 * Sub-classes of FtpClientProvider provide an implementation of {@link FtpClient}
35 * and associated classes. Applications do not normally use this class directly.
36 * See {@link #provider() } for how providers are found and loaded.
37 *
38 * @since 1.7
39 */
40public abstract class FtpClientProvider {
41
42    /**
43     * Creates a FtpClient from this provider.
44     *
45     * @return The created {@link FtpClient}.
46     */
47    public abstract FtpClient createFtpClient();
48    private static final Object lock = new Object();
49    private static FtpClientProvider provider = null;
50
51    /**
52     * Initializes a new instance of this class.
53     *
54     * @throws SecurityException if a security manager is installed and it denies
55     *         {@link RuntimePermission}<tt>("ftpClientProvider")</tt>
56     */
57    protected FtpClientProvider() {
58        SecurityManager sm = System.getSecurityManager();
59        if (sm != null) {
60            sm.checkPermission(new RuntimePermission("ftpClientProvider"));
61        }
62    }
63
64    private static boolean loadProviderFromProperty() {
65        String cm = System.getProperty("sun.net.ftpClientProvider");
66        if (cm == null) {
67            return false;
68        }
69        try {
70            Class<?> c = Class.forName(cm, true, null);
71            provider = (FtpClientProvider) c.newInstance();
72            return true;
73        } catch (ClassNotFoundException |
74                 IllegalAccessException |
75                 InstantiationException |
76                 SecurityException x) {
77            throw new ServiceConfigurationError(x.toString());
78        }
79    }
80
81    private static boolean loadProviderAsService() {
82//        Iterator<FtpClientProvider> i =
83//                ServiceLoader.load(FtpClientProvider.class,
84//                                   ClassLoader.getSystemClassLoader()).iterator();
85//
86//        while (i.hasNext()) {
87//            try {
88//                provider = i.next();
89//                return true;
90//            } catch (ServiceConfigurationError sce) {
91//                if (sce.getCause() instanceof SecurityException) {
92//                    // Ignore, try next provider, if any
93//                    continue;
94//                }
95//                throw sce;
96//            }
97//        }
98        return false;
99    }
100
101    /**
102     * Returns the system wide default FtpClientProvider for this invocation of
103     * the Java virtual machine.
104     *
105     * <p> The first invocation of this method locates the default provider
106     * object as follows: </p>
107     *
108     * <ol>
109     *
110     *   <li><p> If the system property
111     *   <tt>java.net.FtpClientProvider</tt> is defined then it is
112     *   taken to be the fully-qualified name of a concrete provider class.
113     *   The class is loaded and instantiated; if this process fails then an
114     *   unspecified unchecked error or exception is thrown.  </p></li>
115     *
116     *   <li><p> If a provider class has been installed in a jar file that is
117     *   visible to the system class loader, and that jar file contains a
118     *   provider-configuration file named
119     *   <tt>java.net.FtpClientProvider</tt> in the resource
120     *   directory <tt>META-INF/services</tt>, then the first class name
121     *   specified in that file is taken.  The class is loaded and
122     *   instantiated; if this process fails then an unspecified unchecked error or exception is
123     *   thrown.  </p></li>
124     *
125     *   <li><p> Finally, if no provider has been specified by any of the above
126     *   means then the system-default provider class is instantiated and the
127     *   result is returned.  </p></li>
128     *
129     * </ol>
130     *
131     * <p> Subsequent invocations of this method return the provider that was
132     * returned by the first invocation.  </p>
133     *
134     * @return  The system-wide default FtpClientProvider
135     */
136    public static FtpClientProvider provider() {
137        synchronized (lock) {
138            if (provider != null) {
139                return provider;
140            }
141            return (FtpClientProvider) AccessController.doPrivileged(
142                    new PrivilegedAction<Object>() {
143
144                        public Object run() {
145                            if (loadProviderFromProperty()) {
146                                return provider;
147                            }
148                            if (loadProviderAsService()) {
149                                return provider;
150                            }
151                            provider = new sun.net.ftp.impl.DefaultFtpClientProvider();
152                            return provider;
153                        }
154                    });
155        }
156    }
157}
158