/*
* 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
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*/
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;
}
});
}
}
}