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 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 * {@code java.net.FtpClientProvider} 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 * {@code java.net.FtpClientProvider} in the resource
120 * directory {@code META-INF/services}, 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 }