itextpdf.jar is a component in iText 5 Java library to provide core functionalities. iText Java library allows you to generate and manage PDF documents.

The Source Code files are provided at iText GitHub site.

You can compile it to generate your JAR file, using pom.xml as the build configuration file.

The source code of itextpdf-5.5.14.jar is provided below:

⏎ com/itextpdf/text/io/PagedChannelRandomAccessSource.java

/*
 *
 * This file is part of the iText (R) project.
    Copyright (c) 1998-2020 iText Group NV
 * Authors: Kevin Day, Bruno Lowagie, et al.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License version 3
 * as published by the Free Software Foundation with the addition of the
 * following permission added to Section 15 as permitted in Section 7(a):
 * FOR ANY PART OF THE COVERED WORK IN WHICH THE COPYRIGHT IS OWNED BY
 * ITEXT GROUP. ITEXT GROUP DISCLAIMS THE WARRANTY OF NON INFRINGEMENT
 * OF THIRD PARTY RIGHTS.
 *
 * This program 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 Affero General License for more
 * details. You should have received a copy of the GNU Affero General License
 * along with this program; if not, see http://www.gnu.org/licenses or write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 * MA, 02110-1301 USA, or download the license from the following URL:
 * http://itextpdf.com/terms-of-use/
 *
 * The interactive user interfaces in modified source and object code versions
 * of this program must display Appropriate Legal Notices, as required under
 * Section 5 of the GNU Affero General License.
 *
 * In accordance with Section 7(b) of the GNU Affero General License, a covered
 * work must retain the producer line in every PDF that is created or
 * manipulated using iText.
 *
 * You can be released from the requirements of the license by purchasing a
 * commercial license. Buying such a license is mandatory as soon as you develop
 * commercial activities involving the iText software without disclosing the
 * source code of your own applications. These activities include: offering paid
 * services to customers as an ASP, serving PDFs on the fly in a web
 * application, shipping iText with a closed source product.
 *
 * For more information, please contact iText Software Corp. at this address:
 * sales@itextpdf.com
 */
package com.itextpdf.text.io;

import java.io.IOException;
import java.nio.channels.FileChannel;
import java.util.Iterator;
import java.util.LinkedList;

/**
 * A RandomAccessSource that is based on an underlying {@link FileChannel}.  The channel is mapped into memory using a paging scheme to allow for efficient reads of very large files.
 * As an implementation detail, we use {@link GroupedRandomAccessSource} functionality, but override to make determination of the underlying
 * mapped page more efficient - and to close each page as another is opened
 * @since 5.3.5
 */
class PagedChannelRandomAccessSource extends GroupedRandomAccessSource implements RandomAccessSource {
	// these values were selected based on parametric testing with extracting text content from a 2.3GB file.  These settings resulted in the best improvement over
	// the single size MRU case (24% speed improvement)
    public static final int DEFAULT_TOTAL_BUFSIZE = 1 << 26; 
    public static final int DEFAULT_MAX_OPEN_BUFFERS = 16;

    /**
     * The size of each of the buffers to use when mapping files into memory.  This must be greater than 0 and less than {@link Integer#MAX_VALUE}
     */
    private final int bufferSize;
    
    /**
     * The channel this source is based on
     */
    private final FileChannel channel;
    
    /**
     * Most recently used list used to hold a number of mapped pages open at a time
     */
    private final MRU<RandomAccessSource> mru;

    /**
     * Constructs a new {@link PagedChannelRandomAccessSource} based on the specified FileChannel, with a default buffer configuration.
     * The default buffer configuration is currently 2^26 total paged bytes, spread across a maximum of 16 active buffers. This arrangement
     * resulted in a 24% speed improvement over the single buffer case in parametric tests extracting text from a 2.3 GB file.
     * @param channel the channel to use as the backing store
     * @throws IOException if the channel cannot be opened or mapped
     */
    public PagedChannelRandomAccessSource(FileChannel channel) throws IOException {
		this(channel, DEFAULT_TOTAL_BUFSIZE, DEFAULT_MAX_OPEN_BUFFERS);
	}
    
    /**
     * Constructs a new {@link PagedChannelRandomAccessSource} based on the specified FileChannel, with a specific buffer size
     * @param channel the channel to use as the backing store
     * @param bufferSize the size of the buffers to use
     * @throws IOException if the channel cannot be opened or mapped
     */
	public PagedChannelRandomAccessSource(final FileChannel channel, final int totalBufferSize, final int maxOpenBuffers) throws IOException {
        super(buildSources(channel, totalBufferSize/maxOpenBuffers));
		this.channel = channel;
        this.bufferSize = totalBufferSize/maxOpenBuffers;
        this.mru = new MRU<RandomAccessSource>(maxOpenBuffers);
	}

	/**
	 * Constructs a set of {@link MappedChannelRandomAccessSource}s for each page (of size bufferSize) of the underlying channel
	 * @param channel the underlying channel
	 * @param bufferSize the size of each page (the last page may be shorter)
	 * @return a list of sources that represent the pages of the channel
	 * @throws IOException if IO fails for any reason
	 */
	private static RandomAccessSource[] buildSources(final FileChannel channel, final int bufferSize) throws IOException{
		long size = channel.size();
		if (size <= 0)
			throw new IOException("File size must be greater than zero");
		
		int bufferCount = (int)(size/bufferSize) + (size % bufferSize == 0 ? 0 : 1);

		MappedChannelRandomAccessSource[] sources = new MappedChannelRandomAccessSource[bufferCount];
        for (int i = 0; i < bufferCount; i++){
        	long pageOffset = (long)i*bufferSize;
        	long pageLength = Math.min(size - pageOffset, bufferSize);
        	sources[i] = new MappedChannelRandomAccessSource(channel, pageOffset, pageLength);
        }
        return sources;
		
	}
	
	@Override
	/**
	 * {@inheritDoc}
	 */
	protected int getStartingSourceIndex(long offset) {
		return (int) (offset / bufferSize);
	}

	@Override
	/**
	 * {@inheritDoc}
	 * For now, close the source that is no longer being used.  In the future, we may implement an MRU that allows multiple pages to be opened at a time
	 */
	protected void sourceReleased(RandomAccessSource source) throws IOException {
		RandomAccessSource old = mru.enqueue(source);
		if (old != null)
			old.close();
	}
	
	@Override
	/**
	 * {@inheritDoc}
	 * Ensure that the source is mapped.  In the future, we may implement an MRU that allows multiple pages to be opened at a time
	 */
	protected void sourceInUse(RandomAccessSource source) throws IOException {
		((MappedChannelRandomAccessSource)source).open();
	}
	
	@Override
    /**
     * {@inheritDoc}
     * Cleans the mapped bytebuffers and closes the channel
     */
    public void close() throws IOException {
    	super.close();
        channel.close();
    }

	private static class MRU<E>{
		/**
		 * The maximum number of entries held by this MRU
		 */
		private final int limit;
		
		/**
		 * Backing list for managing the MRU
		 */
		private LinkedList<E> queue = new LinkedList<E>();

		/**
		 * Constructs an MRU with the specified size
		 * @param limit the limit
		 */
		public MRU(int limit) {
			this.limit = limit;
		}
		
		/**
		 * Adds an element to the MRU.  If the element is already in the MRU, it is moved to the top.
		 * @param newElement the element to add
		 * @return the element that was removed from the MRU to make room for the new element, or null if no element needed to be removed
		 */
		public E enqueue(E newElement){
			// TODO: this check may not be an effective optimization - the GroupedRandomAccessSource already tracks the 'current' source, so it seems unlikely that we would ever hit this code branch
			if (queue.size() > 0 && queue.getFirst() == newElement)
				return null;
			
			for(Iterator<E> it = queue.iterator(); it.hasNext();){
				E element = it.next();
				if (newElement == element){
					it.remove();
					queue.addFirst(newElement);
					return null;
				}
			}
			queue.addFirst(newElement);
			
			if (queue.size() > limit)
				return queue.removeLast();
			
			return null;
		}
	}
}

⏎ com/itextpdf/text/io/PagedChannelRandomAccessSource.java

Or download all of them as a single archive file:

File name: itextpdf-5.5.14-fyi.zip
File size: 2163839 bytes
Release date: 2009-10-09
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⇒ iText-2.1.6.jar - iText, a JAVA-PDF library

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