/*
 * Copyright 2001-2004 The Apache Software Foundation
 *
 * Licensed 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.net.ftp;
import java.io.BufferedReader;
import java.io.IOException;
import java.util.List;

/**
 * FTPFileEntryParser defines the interface for parsing a single FTP file
 * listing and converting that information into an
 * <a href="org.apache.commons.net.ftp.FTPFile.html"> FTPFile </a> instance.
 * Sometimes you will want to parse unusual listing formats, in which
 * case you would create your own implementation of FTPFileEntryParser and
 * if necessary, subclass FTPFile.
 * <p>
 * Here are some examples showing how to use one of the classes that
 * implement this interface.
 * <p>
 * The first example shows how to get an <b>iterable</b> list of files in which the
 * more expensive <code>FTPFile</code> objects are not created until needed.  This
 * is suitable for paged displays.   It requires that a parser object be created
 * beforehand: <code>parser</code> is an object (in the package
 * <code>org.apache.commons.net.ftp.parser</code>)
 * implementing this inteface.
 *
 * <pre>
 *    FTPClient f=FTPClient();
 *    f.connect(server);
 *    f.login(username, password);
 *    FTPFileList list = f.createFileList(directory, parser);
 *    FTPFileIterator iter = list.iterator();
 *
 *    while (iter.hasNext()) {
 *       FTPFile[] files = iter.getNext(25);  // "page size" you want
 *       //do whatever you want with these files, display them, etc.
 *       //expensive FTPFile objects not created until needed.
 *    }
 * </pre>
 *
 * The second example uses the revised <code>FTPClient.listFiles()</code>
 * API to pull the whole list from the subfolder <code>subfolder</code> in
 * one call, attempting to automatically detect the parser type.  This
 * method, without a parserKey parameter, indicates that autodection should
 * be used.
 *
 * <pre>
 *    FTPClient f=FTPClient();
 *    f.connect(server);
 *    f.login(username, password);
 *    FTPFile[] files = f.listFiles("subfolder");
 * </pre>
 *
 * The third example uses the revised <code>FTPClient.listFiles()</code>>
 * API to pull the whole list from the current working directory in one call,
 * but specifying by classname the parser to be used.  For this particular
 * parser class, this approach is necessary since there is no way to
 * autodetect this server type.
 *
 * <pre>
 *    FTPClient f=FTPClient();
 *    f.connect(server);
 *    f.login(username, password);
 *    FTPFile[] files = f.listFiles(
 *      "org.apache.commons.net.ftp.parser.EnterpriseUnixFTPFileEntryParser",
 *      ".");
 * </pre>
 *
 * The fourth example uses the revised <code>FTPClient.listFiles()</code>
 * API to pull a single file listing in an arbitrary directory in one call,
 * specifying by KEY the parser to be used, in this case, VMS.
 *
 * <pre>
 *    FTPClient f=FTPClient();
 *    f.connect(server);
 *    f.login(username, password);
 *    FTPFile[] files = f.listFiles("VMS", "subfolder/foo.java");
 * </pre>
 *
 * @author <a href="mailto:scohen@apache.org">Steve Cohen</a>
 * @version $Id: FTPFileEntryParser.java,v 1.19 2004/04/21 23:30:33 scohen Exp $
 * @see org.apache.commons.net.ftp.FTPFile
 * @see org.apache.commons.net.ftp.FTPClient#createFileList
 */
public interface FTPFileEntryParser
{
    /**
     * Parses a line of an FTP server file listing and converts it into a usable
     * format in the form of an <code> FTPFile </code> instance.  If the
     * file listing line doesn't describe a file, <code> null </code> should be
     * returned, otherwise a <code> FTPFile </code> instance representing the
     * files in the directory is returned.
     * <p>
     * @param listEntry A line of text from the file listing
     * @return An FTPFile instance corresponding to the supplied entry
     */
    FTPFile parseFTPEntry(String listEntry);

    /**
     * Reads the next entry using the supplied BufferedReader object up to
     * whatever delemits one entry from the next.  Implementors must define
     * this for the particular ftp system being parsed.  In many but not all
     * cases, this can be defined simply by calling BufferedReader.readLine().
     *
     * @param reader The BufferedReader object from which entries are to be
     * read.
     *
     * @return A string representing the next ftp entry or null if none found.
     * @exception IOException thrown on any IO Error reading from the reader.
     */
    String readNextEntry(BufferedReader reader) throws IOException;


    /**
     * This method is a hook for those implementors (such as
     * VMSVersioningFTPEntryParser, and possibly others) which need to
     * perform some action upon the FTPFileList after it has been created
     * from the server stream, but before any clients see the list.
     *
     * The default implementation can be a no-op.
     *
     * @param original Original list after it has been created from the server stream
     *
     * @return Original list as processed by this method.
     */
    List preParse(List original);


}


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