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}{@code ("ftpClientProvider")}
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            @SuppressWarnings("deprecation")
71            Object o = Class.forName(cm, true, null).newInstance();
72            provider = (FtpClientProvider)o;
73            return true;
74        } catch (ClassNotFoundException |
75                 IllegalAccessException |
76                 InstantiationException |
77                 SecurityException x) {
78            throw new ServiceConfigurationError(x.toString());
79        }
80    }
81
82    private static boolean loadProviderAsService() {
83//        Iterator<FtpClientProvider> i =
84//                ServiceLoader.load(FtpClientProvider.class,
85//                                   ClassLoader.getSystemClassLoader()).iterator();
86//
87//        while (i.hasNext()) {
88//            try {
89//                provider = i.next();
90//                return true;
91//            } catch (ServiceConfigurationError sce) {
92//                if (sce.getCause() instanceof SecurityException) {
93//                    // Ignore, try next provider, if any
94//                    continue;
95//                }
96//                throw sce;
97//            }
98//        }
99        return false;
100    }
101
102    /**
103     * Returns the system wide default FtpClientProvider for this invocation of
104     * the Java virtual machine.
105     *
106     * <p> The first invocation of this method locates the default provider
107     * object as follows: </p>
108     *
109     * <ol>
110     *
111     *   <li><p> If the system property
112     *   {@code java.net.FtpClientProvider} is defined then it is
113     *   taken to be the fully-qualified name of a concrete provider class.
114     *   The class is loaded and instantiated; if this process fails then an
115     *   unspecified unchecked error or exception is thrown.  </p></li>
116     *
117     *   <li><p> If a provider class has been installed in a jar file that is
118     *   visible to the system class loader, and that jar file contains a
119     *   provider-configuration file named
120     *   {@code java.net.FtpClientProvider} in the resource
121     *   directory {@code META-INF/services}, then the first class name
122     *   specified in that file is taken.  The class is loaded and
123     *   instantiated; if this process fails then an unspecified unchecked error or exception is
124     *   thrown.  </p></li>
125     *
126     *   <li><p> Finally, if no provider has been specified by any of the above
127     *   means then the system-default provider class is instantiated and the
128     *   result is returned.  </p></li>
129     *
130     * </ol>
131     *
132     * <p> Subsequent invocations of this method return the provider that was
133     * returned by the first invocation.  </p>
134     *
135     * @return  The system-wide default FtpClientProvider
136     */
137    public static FtpClientProvider provider() {
138        synchronized (lock) {
139            if (provider != null) {
140                return provider;
141            }
142            return (FtpClientProvider) AccessController.doPrivileged(
143                    new PrivilegedAction<Object>() {
144
145                        public Object run() {
146                            if (loadProviderFromProperty()) {
147                                return provider;
148                            }
149                            if (loadProviderAsService()) {
150                                return provider;
151                            }
152                            provider = new sun.net.ftp.impl.DefaultFtpClientProvider();
153                            return provider;
154                        }
155                    });
156        }
157    }
158}
159