src/main/java/org/apache/commons/net/ftp/FTPListParseEngine.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
 *
 *      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.io.InputStream;
import java.io.InputStreamReader;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;


/**
 * This class handles the entire process of parsing a listing of
 * file entries from the server.
 * <p>
 * This object defines a two-part parsing mechanism.
 * <p>
 * The first part is comprised of reading the raw input into an internal
 * list of strings.  Every item in this list corresponds to an actual
 * file.  All extraneous matter emitted by the server will have been
 * removed by the end of this phase.  This is accomplished in conjunction
 * with the FTPFileEntryParser associated with this engine, by calling
 * its methods <code>readNextEntry()</code> - which handles the issue of
 * what delimits one entry from another, usually but not always a line
 * feed and <code>preParse()</code> - which handles removal of
 * extraneous matter such as the preliminary lines of a listing, removal
 * of duplicates on versioning systems, etc.
 * <p>
 * The second part is composed of the actual parsing, again in conjunction
 * with the particular parser used by this engine.  This is controlled
 * by an iterator over the internal list of strings.  This may be done
 * either in block mode, by calling the <code>getNext()</code> and
 * <code>getPrevious()</code> methods to provide "paged" output of less
 * than the whole list at one time, or by calling the
 * <code>getFiles()</code> method to return the entire list.
 * <p>
 * Examples:
 * <p>
 * Paged access:
 * <pre>
 *    FTPClient f=FTPClient();
 *    f.connect(server);
 *    f.login(username, password);
 *    FTPListParseEngine engine = f.initiateListParsing(directory);
 *
 *    while (engine.hasNext()) {
 *       FTPFile[] files = engine.getNext(25);  // "page size" you want
 *       //do whatever you want with these files, display them, etc.
 *       //expensive FTPFile objects not created until needed.
 *    }
 * </pre>
 * <p>
 * For unpaged access, simply use FTPClient.listFiles().  That method
 * uses this class transparently.
 * @version $Id$
 */
public class FTPListParseEngine {
    private List<String> entries = new LinkedList<String>();
    private ListIterator<String> _internalIterator = entries.listIterator();

    FTPFileEntryParser parser = null;

    public FTPListParseEngine(FTPFileEntryParser parser) {
        this.parser = parser;
    }

    /**
     * handle the initial reading and preparsing of the list returned by
     * the server.  After this method has completed, this object will contain
     * a list of unparsed entries (Strings) each referring to a unique file
     * on the server.
     *
     * @param stream input stream provided by the server socket.
     *
     * @exception IOException
     *                   thrown on any failure to read from the sever.
     */
    public void readServerList(InputStream stream, String encoding)
    throws IOException
    {
        this.entries = new LinkedList<String>();
        readStream(stream, encoding);
        this.parser.preParse(this.entries);
        resetIterator();
    }
    
  
    /**
     * Internal method for reading the input into the <code>entries</code> list.
     * After this method has completed, <code>entries</code> will contain a
     * collection of entries (as defined by
     * <code>FTPFileEntryParser.readNextEntry()</code>), but this may contain
     * various non-entry preliminary lines from the server output, duplicates,
     * and other data that will not be part of the final listing.
     *
     * @param stream The socket stream on which the input will be read.
     * @param encoding The encoding to use.
     *
     * @exception IOException
     *                   thrown on any failure to read the stream
     */
    private void readStream(InputStream stream, String encoding) throws IOException
    {
        BufferedReader reader;
        if (encoding == null)
        {
            reader = new BufferedReader(new InputStreamReader(stream));
        }
        else
        {
            reader = new BufferedReader(new InputStreamReader(stream, encoding));
        }
        
        String line = this.parser.readNextEntry(reader);

        while (line != null)
        {
            this.entries.add(line);
            line = this.parser.readNextEntry(reader);
        }
        reader.close();
    }

    /**
     * Returns an array of at most <code>quantityRequested</code> FTPFile
     * objects starting at this object's internal iterator's current position.
     * If fewer than <code>quantityRequested</code> such
     * elements are available, the returned array will have a length equal
     * to the number of entries at and after after the current position.
     * If no such entries are found, this array will have a length of 0.
     *
     * After this method is called this object's internal iterator is advanced
     * by a number of positions equal to the size of the array returned.
     *
     * @param quantityRequested
     * the maximum number of entries we want to get.
     *
     * @return an array of at most <code>quantityRequested</code> FTPFile
     * objects starting at the current position of this iterator within its
     * list and at least the number of elements which  exist in the list at
     * and after its current position.
     * <p><b> 
     * NOTE:</b> This array may contain null members if any of the 
     * individual file listings failed to parse.  The caller should 
     * check each entry for null before referencing it.
     */
    public FTPFile[] getNext(int quantityRequested) {
        List<FTPFile> tmpResults = new LinkedList<FTPFile>();
        int count = quantityRequested;
        while (count > 0 && this._internalIterator.hasNext()) {
            String entry = this._internalIterator.next();
            FTPFile temp = this.parser.parseFTPEntry(entry);
            tmpResults.add(temp);
            count--;
        }
        return tmpResults.toArray(new FTPFile[0]);

    }

    /**
     * Returns an array of at most <code>quantityRequested</code> FTPFile
     * objects starting at this object's internal iterator's current position,
     * and working back toward the beginning.
     *
     * If fewer than <code>quantityRequested</code> such
     * elements are available, the returned array will have a length equal
     * to the number of entries at and after after the current position.
     * If no such entries are found, this array will have a length of 0.
     *
     * After this method is called this object's internal iterator is moved
     * back by a number of positions equal to the size of the array returned.
     *
     * @param quantityRequested
     * the maximum number of entries we want to get.
     *
     * @return an array of at most <code>quantityRequested</code> FTPFile
     * objects starting at the current position of this iterator within its
     * list and at least the number of elements which  exist in the list at
     * and after its current position.  This array will be in the same order
     * as the underlying list (not reversed).
     * <p><b> 
     * NOTE:</b> This array may contain null members if any of the 
     * individual file listings failed to parse.  The caller should 
     * check each entry for null before referencing it.
     */
    public FTPFile[] getPrevious(int quantityRequested) {
        List<FTPFile> tmpResults = new LinkedList<FTPFile>();
        int count = quantityRequested;
        while (count > 0 && this._internalIterator.hasPrevious()) {
            String entry = this._internalIterator.previous();
            FTPFile temp = this.parser.parseFTPEntry(entry);
            tmpResults.add(0,temp);
            count--;
        }
        return tmpResults.toArray(new FTPFile[0]);
    }

    /**
     * Returns an array of FTPFile objects containing the whole list of
     * files returned by the server as read by this object's parser.
     *
     * @return an array of FTPFile objects containing the whole list of
     *         files returned by the server as read by this object's parser.
     * <p><b> 
     * NOTE:</b> This array may contain null members if any of the 
     * individual file listings failed to parse.  The caller should 
     * check each entry for null before referencing it.
     * @exception IOException
     */
    public FTPFile[] getFiles()
    throws IOException
    {
        List<FTPFile> tmpResults = new LinkedList<FTPFile>();
        Iterator<String> iter = this.entries.iterator();
        while (iter.hasNext()) {
            String entry = iter.next();
            FTPFile temp = this.parser.parseFTPEntry(entry);
            tmpResults.add(temp);
        }
        return tmpResults.toArray(new FTPFile[0]);

    }

    /**
     * convenience method to allow clients to know whether this object's
     * internal iterator's current position is at the end of the list.
     *
     * @return true if internal iterator is not at end of list, false
     * otherwise.
     */
    public boolean hasNext() {
        return _internalIterator.hasNext();
    }

    /**
     * convenience method to allow clients to know whether this object's
     * internal iterator's current position is at the beginning of the list.
     *
     * @return true if internal iterator is not at beginning of list, false
     * otherwise.
     */
    public boolean hasPrevious() {
        return _internalIterator.hasPrevious();
    }

    /**
     * resets this object's internal iterator to the beginning of the list.
     */
    public void resetIterator() {
        this._internalIterator = this.entries.listIterator();
    }
}