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/GroupedRandomAccessSource.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;

/**
 * A RandomAccessSource that is based on a set of underlying sources, treating the sources as if they were a contiguous block of data.
 * @since 5.3.5
 */
class GroupedRandomAccessSource implements RandomAccessSource {
    /**
     * The underlying sources (along with some meta data to quickly determine where each source begins and ends)
     */
	private final SourceEntry[] sources;
    
	/**
	 * Cached value to make multiple reads from the same underlying source more efficient
	 */
    private SourceEntry currentSourceEntry;

    /**
     * Cached size of the underlying channel
     */
    private final long size;



    /**
     * Constructs a new {@link GroupedRandomAccessSource} based on the specified set of sources
     * @param sources the sources used to build this group
     */
	public GroupedRandomAccessSource(RandomAccessSource[] sources) throws IOException {
        this.sources = new SourceEntry[sources.length];
        
        long totalSize = 0;
        for(int i = 0; i < sources.length; i++){
        	this.sources[i] = new SourceEntry(i, sources[i], totalSize);
        	totalSize += sources[i].length();
        }
        size = totalSize;
        currentSourceEntry = this.sources[sources.length-1];
        sourceInUse(currentSourceEntry.source);
	}

	/**
	 * For a given offset, return the index of the source that contains the specified offset.
	 * This is an optimization feature to help optimize the access of the correct source without having to iterate
	 * through every single source each time.  It is safe to always return 0, in which case the full set of sources will be searched.
	 * Subclasses should override this method if they are able to compute the source index more efficiently (for example {@link FileChannelRandomAccessSource} takes advantage of fixed size page buffers to compute the index) 
	 * @param offset the offset
	 * @return the index of the input source that contains the specified offset, or 0 if unknown
	 */
	protected int getStartingSourceIndex(long offset){
        if (offset >= currentSourceEntry.firstByte)
        	return currentSourceEntry.index;

        return 0;
	}
	
	/**
	 * Returns the SourceEntry that contains the byte at the specified offset  
	 * sourceReleased is called as a notification callback so subclasses can take care of cleanup when the source is no longer the active source
	 * @param offset the offset of the byte to look for
	 * @return the SourceEntry that contains the byte at the specified offset
	 * @throws IOException if there is a problem with IO (usually the result of the sourceReleased() call)
	 */
	private SourceEntry getSourceEntryForOffset(long offset) throws IOException {
        if (offset >= size)
        	return null;
        
        if (offset >= currentSourceEntry.firstByte && offset <= currentSourceEntry.lastByte)
        	return currentSourceEntry;
        
        // hook to allow subclasses to release resources if necessary
        sourceReleased(currentSourceEntry.source);
        
        int startAt = getStartingSourceIndex(offset);
        
        for(int i = startAt; i < sources.length; i++){ 
        	if (offset >= sources[i].firstByte && offset <= sources[i].lastByte){
        		currentSourceEntry = sources[i];
        		sourceInUse(currentSourceEntry.source);
        		return currentSourceEntry;
        	}
        }
        
        return null;
		
	}
	
	/**
	 * Called when a given source is no longer the active source.  This gives subclasses the abilty to release resources, if appropriate. 
	 * @param source the source that is no longer the active source
	 * @throws IOException if there are any problems
	 */
	protected void sourceReleased(RandomAccessSource source) throws IOException{
		// by default, do nothing
	}
	
	/**
	 * Called when a given source is about to become the active source.  This gives subclasses the abilty to retrieve resources, if appropriate. 
	 * @param source the source that is about to become the active source
	 * @throws IOException if there are any problems
	 */
	protected void sourceInUse(RandomAccessSource source) throws IOException{
		// by default, do nothing
	}
	
    /** 
     * {@inheritDoc} 
     * The source that contains the byte at position is retrieved, the correct offset into that source computed, then the value
     * from that offset in the underlying source is returned.
     */  
	public int get(long position) throws IOException {
		SourceEntry entry = getSourceEntryForOffset(position);
		
        if (entry == null) // we have run out of data to read from
        	return -1;
        
        return entry.source.get(entry.offsetN(position));

	}
	
    /** 
     * {@inheritDoc} 
     */  
	public int get(long position, byte[] bytes, int off, int len) throws IOException {
		SourceEntry entry = getSourceEntryForOffset(position);
		
        if (entry == null) // we have run out of data to read from
        	return -1;
		
        long offN = entry.offsetN(position);

        int remaining = len;
        
        while(remaining > 0){
            if (entry == null) // we have run out of data to read from
                break;
            if (offN > entry.source.length())
                break;
            
            int count = entry.source.get(offN, bytes, off, remaining);
            if (count == -1)
            	break;
            
            off += count;
            position += count;
            remaining -= count;

            offN = 0;
            entry = getSourceEntryForOffset(position);
        }
        return remaining == len ? -1 : len - remaining;	
    }

	
    /** 
     * {@inheritDoc} 
     */  
	public long length() {
		return size;
	}

    /**
     * {@inheritDoc}
     * Closes all of the underlying sources
     */
    public void close() throws IOException {
        for (SourceEntry entry : sources) {
			entry.source.close();
		}
    }

    /**
     * Used to track each source, along with useful meta data 
     */
    private static class SourceEntry{
    	/**
    	 * The underlying source
    	 */
    	final RandomAccessSource source;
    	/**
    	 * The first byte (in the coordinates of the GroupedRandomAccessSource) that this source contains
    	 */
    	final long firstByte;
    	/**
    	 * The last byte (in the coordinates of the GroupedRandomAccessSource) that this source contains
    	 */
    	final long lastByte;
    	/**
    	 * The index of this source in the GroupedRandomAccessSource
    	 */
    	final int index;
    	
    	/**
    	 * Standard constructor
    	 * @param index the index
    	 * @param source the source
    	 * @param offset the offset of the source in the GroupedRandomAccessSource
    	 */
    	public SourceEntry(int index, RandomAccessSource source, long offset) {
			this.index = index;
    		this.source = source;
			this.firstByte = offset;
			this.lastByte = offset + source.length() - 1;
		}
    	
    	/**
    	 * Given an absolute offset (in the GroupedRandomAccessSource coordinates), calculate the effective offset in the underlying source
    	 * @param absoluteOffset the offset in the parent GroupedRandomAccessSource
    	 * @return the effective offset in the underlying source
    	 */
    	public long offsetN(long absoluteOffset){
    		return absoluteOffset - firstByte;
    	}
    }
}

⏎ com/itextpdf/text/io/GroupedRandomAccessSource.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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