src/main/java/org/apache/commons/net/ftp/FTPFileEntryParser.java

/*
 * 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
 *
 *      https://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
 * {@link org.apache.commons.net.ftp.FTPFile} 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>
 * <p>
 * The first example uses the {@code FTPClient.listFiles()} API to pull the whole list from the subfolder {@code subfolder} in one call, attempting to
 * automatically detect the parser type. This method, without a parserKey parameter, indicates that autodection should be used.
 * </p>
 *
 * <pre>
 * FTPClient f = FTPClient();
 * f.connect(server);
 * f.login(user, password);
 * FTPFile[] files = f.listFiles("subfolder");
 * </pre>
 *
 * The second example uses the {@code FTPClient.listFiles()} API to pull the whole list from the current working directory in one call, but specifying by
 * class name 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(user, password);
 * FTPFile[] files = f.listFiles("org.apache.commons.net.ftp.parser.EnterpriseUnixFTPFileEntryParser", ".");
 * </pre>
 *
 * The third example uses the {@code FTPClient.listFiles()} 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(user, password);
 * FTPFile[] files = f.listFiles("VMS", "subfolder/foo.java");
 * </pre>
 * <p>
 * For an alternative approach, see the {@link FTPListParseEngine} class which provides iterative access.
 * </p>
 *
 * @see org.apache.commons.net.ftp.FTPFile
 * @see org.apache.commons.net.ftp.FTPClient#listFiles()
 */
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} instance. If the file listing
     * line doesn't describe a file, {@code null} should be returned, otherwise a {@code FTPFile} instance representing the files in the directory
     * is returned.
     *
     * @param listEntry A line of text from the file listing
     * @return An FTPFile instance corresponding to the supplied entry
     */
    FTPFile parseFTPEntry(String listEntry);

    /**
     * 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<String> preParse(List<String> original);

    /**
     * Reads the next entry using the supplied BufferedReader object up to whatever delimits 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.
     * @throws IOException thrown on any IO Error reading from the reader.
     */
    String readNextEntry(BufferedReader reader) throws IOException;

}