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Apache Commons VFS is a Virtual File System library.
There is a newer version: 2.9.0
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.vfs2.provider.ftp;

import java.io.IOException;
import java.util.Collection;
import java.util.concurrent.atomic.AtomicReference;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.commons.vfs2.Capability;
import org.apache.commons.vfs2.FileObject;
import org.apache.commons.vfs2.FileSystemException;
import org.apache.commons.vfs2.FileSystemOptions;
import org.apache.commons.vfs2.VfsLog;
import org.apache.commons.vfs2.provider.AbstractFileName;
import org.apache.commons.vfs2.provider.AbstractFileSystem;
import org.apache.commons.vfs2.provider.GenericFileName;

/**
 * An FTP file system.
 */
public class FtpFileSystem extends AbstractFileSystem {
    private static final Log LOG = LogFactory.getLog(FtpFileSystem.class);

    // private final String hostname;
    // private final int port;
    // private final String username;
    // private final String password;

    // An idle client
    private final AtomicReference idleClient = new AtomicReference<>();

    /**
     * @param rootName The root of the file system.
     * @param ftpClient The FtpClient.
     * @param fileSystemOptions The FileSystemOptions.
     * @since 2.0 (was protected)
     */
    public FtpFileSystem(final GenericFileName rootName, final FtpClient ftpClient,
            final FileSystemOptions fileSystemOptions) {
        super(rootName, null, fileSystemOptions);
        // hostname = rootName.getHostName();
        // port = rootName.getPort();

        idleClient.set(ftpClient);
    }

    @Override
    protected void doCloseCommunicationLink() {
        final FtpClient idle = idleClient.getAndSet(null);
        // Clean up the connection
        if (idle != null) {
            closeConnection(idle);
        }
    }

    /**
     * Adds the capabilities of this file system.
     */
    @Override
    protected void addCapabilities(final Collection caps) {
        caps.addAll(FtpFileProvider.capabilities);
    }

    /**
     * Cleans up the connection to the server.
     *
     * @param client The FtpClient.
     */
    private void closeConnection(final FtpClient client) {
        try {
            // Clean up
            if (client.isConnected()) {
                client.disconnect();
            }
        } catch (final IOException e) {
            // getLogger().warn("vfs.provider.ftp/close-connection.error", e);
            VfsLog.warn(getLogger(), LOG, "vfs.provider.ftp/close-connection.error", e);
        }
    }

    /**
     * Creates an FTP client to use.
     *
     * @return An FTPCleint.
     * @throws FileSystemException if an error occurs.
     */
    public FtpClient getClient() throws FileSystemException {
        FtpClient client = idleClient.getAndSet(null);

        if (client == null || !client.isConnected()) {
            client = createWrapper();
        }

        return client;
    }

    /**
     * Get the wrapper to access this file system.
     *
     * @return new instance.
     * @throws FileSystemException if any error occurs.
     * @since 2.1
     */
    protected FTPClientWrapper createWrapper() throws FileSystemException {
        return new FTPClientWrapper((GenericFileName) getRoot().getName(), getFileSystemOptions());
    }

    /**
     * Returns an FTP client after use.
     *
     * @param client The FTPClient.
     */
    public void putClient(final FtpClient client) {
        // Save client for reuse if none is idle.
        if (!idleClient.compareAndSet(null, client)) {
            // An idle client is already present so close the connection.
            closeConnection(client);
        }
    }

    /**
     * Creates a file object.
     */
    @Override
    protected FileObject createFile(final AbstractFileName name) throws FileSystemException {
        return new FtpFileObject(name, this, getRootName());
    }
}