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 */
25 package sun.net.ftp;
26
27 import java.security.AccessController;
28 import java.security.PrivilegedAction;
29 import 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 */
40 public 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 }